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458 Cards in this Set
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(MID #1)
What is the purpose of a Gram stain? How does one distinguish between Gram Positive and Gram Negative Bacteria? |
Slides are sequentially stained with crystal violet, iodine, and then destained with alcohol and counter-stained with safranin. Gram positive bacteria stain blue-purple and Gram negative bacteria stain red. Gram (+)'s have a much larger PEPTIDOGLYCAN WALL, so the iodine and crystal violet precipitate in the thickened cell wall and are not eluted by alcohol. Crystal violet is readily eluted from Gram (-) bacteria, which accounts for their pinkish-red appearance.
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(MID #2)
Distinguish between facultative anaerobic, strictly anaerobic, strictly aerobic, and microaerophilic bacteria. |
Facultatively anaerobic bacteria can grow in high oxygen or low oxygen content and are among the most versatile bacteria.
Strictly aerobic bacteria only grow in the presence of significant quantities of oxygen. (e.g., P. aeruginosa) Strictly anaerobic bacteria grow only in conditions with minimal or no oxygen present in the environment. (e.g., Bacteroides in the colon) Microaerophilic bacteria grow under conditions of reduced oxygen adn sometimes require increased levels of carbon dioxide. (e.g., Neisseria species) |
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(MID #3)
Why is it important to consider environmental or endogenous reservoirs when considering likely pathogens? |
Endogenous reservoirs account for LOTS of human infections. Staph epidermidis colonizes the skin. Staph aureus is part of the commensal flora of the anterior nares. Viridans streptococcus is part of the normal oropharyngeal flora.
*Abscess following large bowel surgery -> caused by an anaerobic resident of the large bowel. *Skin rash in a hiker with a history of tick bites -> Borrelia, the agent of Lyme disease *Outbreak of food poisoning traced to unpasteurized cheese -> Listeria |
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(MID #4)
When would you use Ribosomal RNA Sequence Analysis to diagnose a particular pathogen? What about Molecular Subtyping? |
rRNA Sequence Analysis has been used to establish a phylogenetic tree, can rapidly diagnose which pathogen is responsible for an infection, and can help clinicians to identify and/or select an appropriate therapy for noncultivatable organisms.
Molecular Subtyping: If an outbreak of infections due to the same bacterial species appears in a hospital, the hospital epidemiologist will want to know if all the infections were caused by the same strain. This test is done by pulsed field gel electrophoresis. |
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(MID #5)
Common Features of Bacteria Include: Slime -> What is it good for? Capule -> Prevents what by immune cells? Peptidoglycan -> This is a primary target for antimicrobials. Why?? |
"SLIME" is extracellular polysaccharide, elaborated by some bacterial species. Facilitates colonization of smooth, prosthetic surfaces such as intravascular catheters.
The CAPSULE is the bacteria's outer covering, made of polysaccharide. It often has an anti-phagocytic role. PEPTIDOGLYCAN provides bacterial shape and rigidity. It consists of alternating chains of N-acetylglucosamine and N-acetylmuramic acid. Polysaccharide chains are X-linked by a peptide bridge. Peptidoglycan is specific to prokaryotes so it's a TARGET for antimicrobials. (**The final step in the transpeptidation rxn is catalyzed by a transpeptidase enzyme called penicillin-binding protein that crosslinks the growing strand with others.) |
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(MID #6)
Common Features of Bacteria Include: * Cytoplasmic Membrane * Flagella * Pili * Secreted Products |
CYTOPLASMIC MEMBRANE: phospholipid bilayer, assumes functions of eukaryotic organisms such as biosynthetic processes.
FLAGELLA: locomotion PILI: Enable bacteria to adhere to host tissue surfaces. Can be very specific for particular host tissues. SECRETED PRODUCTS: Mainly exotoxins. Include (1) A-B toxins, (2) membrane damaging toxins, and (3) hydrolytic enzymes that destroy host tissues and extracellular matrices. |
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(MID #7)
Distinguish between Gram Positive and Gram Negative Bacteria. (With which of these classes of bacteria is "ENDOTOXIN" associated?) |
Gram Positive Bacteria: Large peptidoglycan accounts for gram staining properties. Some can form SPORES in stressful environments with limited carbon & nitrogen; these can survive extreme conditions and lead to recurrent infection.
Gram Negative Bacteria: Small peptidoglycan. Have an additional outer cytoplasmic membrane which serves as a permeability barrier. *Endotoxin* is a major component of the cytoplasmic membrane that is UNIQUE TO GRAM NEGs. Consists of 3 parts: (1)"Lipid A" moiety; (2)highly conserved "Core Polysaccharide";(3)species-specific "O Antigen" |
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(MID #8)
Endotoxin |
Endotoxin = LPS (lipopolysaccharide). Consist of a lipid A moiety, a highly conserved core polysaccharide, and a species-specific O antigen. Endotoxin is cell-associated, but can be released with cell division or cell death (@ the 2 ends of the spectrum of life!!) The lipid A moiety of endotoxin is responsible for sepsis, causing confusion, fever, decreased BP, and multi-organ failure. Septic shock can be fatal.
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(MID #9)
Staphylococci * morphology * oxygen requirements * commensal? * reservoirs/sites of colonization/transmission * types of infections |
GRAM POSITIVE COCCI in grapelike clusters -> "The Grapes of Staph"!! Facultative anaerobes. Are commensal flora. Hang out in the skin, and nares. Transmitted by direct contact, aerosol, or endogenous.
TYPES OF INFECTIONS: Cause soft tissue, bone, and joint infections; endocarditis; food poisoning. |
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(MID #10)
Streptococci *Morphology *O2 requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE COCCI in pairs or chains. Facultative anaerobe. Some species are commensal. Hang out in the skin and oropharynx. Can be transmitted via direct contact, aerosol, or endogenous.
TYPES OF INFECTIONS: skin; pharyngitis; endocarditis; toxic shock syndrome |
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(MID #11)
Pneumococci *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE lancet-shaped diplococci. Facultative anaerobe. Hang out in the oropharynx and sinuses. Transmission via aerosol. Commensal? +/-
TYPES OF INFECTIONS: pneumonia; otitis; sinusitis; meningitis |
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(MID #11)
Enterococci *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE COCCI in pairs. Facultative anaerobe. YES commensal. Hang out in the GI tract. Transmission via direct contact or endogenous.
TYPES OF INFECTIONS: GI; UTI; Catheter-related infections |
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(MID #13)
BACILLI *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE RODS, spore forming. Aerobic. +/- commensal. Transmission via aerosol, direct contact.
TYPES OF INFECTIONS: anthrax; food poisoning; catheter-related infections |
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(MID #13)
Bacilli *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE RODS, spore forming. Aerobic. Commensal? +/- Transmission via aerosol, direct contact.
TYPES OF INFECTIONS: anthrax; food poisoning; catheter-related infections |
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(MID #14)
CLOSTRIDIA *Morphology *O2 Requirement *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE RODS, spore forming. Anaerobic. Some species are commensal flora. Hang out in the GI tract, the soil. Transmission via breach of skin, ingestion, or endogenous.
TYPES OF INFECTIONS: tetanus; diarrhea; gas gangrene; botulism |
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(MID #15)
CORNYBACTERIUM *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE RODS, non-spore forming. Facultative anaerobe. Some species are commensal flora. Hang out in the skin.
TYPES OF INFECTIONS: catheter-related infections; diphtheria |
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(MID #16)
LISTERIA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE RODS, non-spore forming. Facultative anaerobe. NOT commensal. Colonize animals and food products. Transmitted through ingestion.
TYPES OF INFECTIONS: Meningitis |
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(MID #17)
ACTINOMYCES *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM POSITIVE irregularly shaped, filamentous bacteria that form sulfur granules. Anaerobic. YES commensal. Hang out in the GI tract. Transmission: endogenous.
TYPES OF INFECTIONS: skin; soft tissue |
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(MID #18)
ENTEROBACTERIACEAE (e. coli, klebsiella, salmonella, shigella) *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE RODS. Facultative anaerobe. Some species are commensal flora. Hang out in the GI tract. Colonize some animals. Transmission is fecal->oral.
TYPES OF INFECTIONS: diarrhea; UTI; food poisoning; sepsis |
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(MID #19)
BACTEROIDES *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE RODS. Anaerobic. YES commensal. Hang out in the GI tract. Transmission: endogenous.
TYPES OF INFECTIONS: abscesses; intra-abdominal infections |
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(MID #20)
PSEUDOMONAS *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE RODS. Aerobic. NOT commensal. Colonize water and soil. Transmission: endogenous, breach of skin barrier.
TYPES OF INFECTIONS: opportunistic infections in immunocompromised hosts; cystic fibrosis |
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(MID #21)
VIBRIO CHOLERA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE RODS, curved-shaped. Microaerophilic. NOT commensal. Colonize water. Transmission: contaminated food or water.
TYPES OF INFECTION: Diarrhea |
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(MID #22)
CAMPYLOBACTER *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE RODS, curved shape. Microaerophilic. NOT commensal. Colonize food. Transmitted via ingestion of contaminated food.
TYPES OF INFECTIONS: Diarrhea; Bacteremia |
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(MID #23)
LEGIONELLA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE RODS, poorly stained. Microaerophilic. NOT commensal. Colonize water. Transmission: inhalation of aerosol.
TYPES OF INFECTION: pneumonia; febrile illness |
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(MID #24)
NEISSERIA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE COCCI, kidney-bean shaped. Microaerophilic. NOT commensal (although N. meningitidis can be sometimes). Reservoirs are humans! Transmission: sexual, aerosol.
TYPES OF INFECTIONS: Meningitis; Pelvic Inflammatory Disease |
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(MID #25)
HEMOPHILUS *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
GRAM NEGATIVE coccobacillary pleomorphic bacterium. Facultative anaerobe. Some species are commensal flora. Hang out in the respiratory tract. Transmission: endogenous; aerosol.
TYPES OF INFECTIONS: respiratory; sinusitis; otitis; meningitis |
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(MID #26)
BARTONELLA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
Small, pleomorphic GRAM POSITIVE RODS. Aerobic/Microaerophilic. NOT commensal. Colonize cats, fleas, lice. Transmission: cat bites, lice or fleas.
TYPES OF INFECTIONS: cat scratch disease; endocarditis; bacillary angiomatosis |
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(MID #27)
HELICOBACTER *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
Not visible on a gram stain. Helical (corkscrew shaped). Microaerophilic. YES commensal. Hang out in the stomach. Transmission: Endogenous, Fecal -> Oral.
TYPES OF INFECTIONS: Peptic ulcer disease, gastric ulcers |
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(MID #28)
MYCOBACTERIA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
Weakly GRAM NEGATIVE rods, Acid Fast Stain POSITIVE. Aerobic. NOT commensal. Colonize the lungs. Transmission: fomites.
TYPES OF INFECTIONS: Tuberculosis |
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(MID #29)
TREPONEMES *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
Not visible on a gram stain. Spiral-shaped on a dark field exam. Nonculturable on routine media. NOT commensal. Reservoir is humans. Transmitted through sexual contact.
TYPES OF INFECTIONS: Syphilis |
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(MID #30)
BORRELIA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
Not visible on a Gram stain. Spiral-shaped on dark field exam. Non-culturable on routine media. NOT commensal. Reservoirs are rodents and ticks. Transmitted via tick bites.
TYPES OF INFECTIONS: Lyme disease; relapsing fever |
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(MID #31)
MYCOPLASMA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
Not visible on Gram stain, no cell wall, pleiomorphic. Non-culturable on routine media. Some species are commensal flora. Reservoirs are humans. Transmission: aerosol.
TYPES OF INFECTIONS: Respiratory tract infections |
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(MID #32)
RICKETTSIA/EHRLICHIA *Morphology *O2 Requirements *Commensal? *Reservoirs/Sites of Colonization/Transmission *Types of Infections |
Obligate intracellular, GRAM NEGATIVE but not visible on a gram stain. Non-culturable on routine media. NOT commensal. Reservoirs are mites and ticks. Transmitted through the feces of infected lice, fleas, and ticks.
TYPES OF INFECTIONS: Can cause a variety of illnesses including: systemic vasculitis (e.g., Rocky Mountain Spotted Fever); rash; pneumonia |
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(MID #33)
What are the Henle-Koch postulates? What is the "germ theory" of disease? |
The Henle Koch Postulates: 1)Bacteria should be identified in the lesions of the infection. 2)The bacteria could be isolated in pure culture on artificial media. 3)The disease was reproduced when inoculated into a susceptible animal. 4)The bacteria was recoverable from the infected animal.
The GERM THEORY of disease: Some infectious diseases are contagious (transmitted by contact) while others are communicable (transmitted indirectly by water or insects). This theory was in conflict with the then-current theory that diseases were spread by "miasmas". |
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(MID #34)
Distinguish between a Common Source Outbreak and a Propagated Epidemic. |
Epidemics are outbreaks of infections that are in excess of the normal "endemic" incidence of a particular type of infection. COMMON SOURCE OUTBREAKS are represented by a sharp curve. Point source outbreak with a single site or agent (e.g., food) causing infection. If you eliminate the source, you eliminate the epidemic. A PROPAGATED EPIDEMIC occurs when a wave of individuals acquires the infection and due to the presence of susceptible subjects, secondary cases occur (e.g., chicken pox). Continues until enough of the community members have developed immunity and are protected from subsequent infection.
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(MID #35)
Distinguish between primary and opportunistic pathogens. |
Primary pathogens are capable of causing disease in normal hosts. Opportunistic pathogens primarily cause disease in immunocompromised individuals. Highly pathogenic organisms can cause disease with a small number of organisms (Shigella spp) while other organisms (Staph epidermidis) require special settings or a high bacterial inoculum.
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(MID #36)
Discuss INFECTION |
Infection refers to the ability of microorganisms to invade tissue adn find conditions that are suitable for growth and replication. It is NOT in the interests of organisms to destroy the host. It is the exception for microorganisms to cause infection, not the rule. Alterations in site of colonization, bacterial density, or level of host immunocompetence alter the likelihood of infection. Infection can be a function of the host's response to the microorganism. Infections may cause either clinical (apparent) or subclinical (inapparent) illness. Many individuals develop an immune response to a pathogen without manifesting any signs of illness.
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(MID #37)
Can you have bacterial disease/illness in the absence of bacterial infection? |
Some pathogens can cause disease by the elaboration of a toxin, which can occur in the absence of viable bacteria. Certain types of food poisoning are caused this way.
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(MID #38)
What does a disease CARRIER look like? (In the infectious disease sense of the word, NOT the genetic sense.) |
A CARRIER is an individual with asymptomatic colonization or infection who is capable of transmitting infection to tohers. The patient may or may not be ill himself (e.g., hepatitis C). Historically, "Typhoid Mary" was responsible for several outbreaks of Salmonella typhi infections in the Northeast.
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(MID #39)
Define LATENCY |
Pathogen remains viable but is dormant within the host. Remains capable of causing disease at a later date. Examples include Mycobacteria tuberculosis and herpes virus.
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(MID #40)
Discuss RESERVOIRS in the context of the "Infectious Disease Cycle" |
Reservoirs for bacterial pathogens are divided into humans (the most common animate reservoir), animals, soil & water. Knowing the reservoir and the exposure history of the patient is often helpful in establishing the likely pathogen. A farmer with a puncture wound from a stray nail is more likely to have an infection caused by a soil pathogen such as Clostridia than a pathogen carried by water (Legionella).
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(MID #41)
Discuss PATTERNS OF TRANSMISSION in the context of "The Infectious Disease Cycle" |
Infections can be acquired from within the host (ENDOGENOUS) or without (EXOGENOUS). Endogenous infections usually result from an alteration in the equilibrium between the host and the pathogen. The host may become immunocompromised, a commensal may be innoculated into a sterile site, or antibiotics may alter the 'normal' or indigenous microbial flora. Exogenous infections may spread by horizontal transmission (spread to unrelated individuals) or by vertical transmission (spread from parents to offspring). Examples of horizontal transmission include sexual contact or water-borne spread.
There are several means of microbial transmission including person-person (respiratory secretions, fecal-oral contamination); vector-borne (mosquitoes, ticks); animals (dogs, cats); or environmental (food, water). |
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(MID #42)
Discuss PORTALS OF ENTRY for pathogens. |
Numerous means of inoculation including breaches in the skin, inhalation, and ingestion. Each organ system has its own unique host defense mechanisms that must be bypassed in order for an infection to be established.
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(MID #43)
What is the "Iceberg Model of Infection"? |
This is the idea that infections range from subclinical to full-blown life-threatening disease, but MOST infections are subclinical and are detected only when serologic or other sensitive assays become available for recognition of past exposure. There are exceptions, however, with diseases such as Rabies and HIV that cause overt disease in virtually everyone infected.
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(MID #44)
CAUTION. Many DIFFERENT bacterial species can cause the SAME infectious disease syndrome, while the SAME bacterial species can also cause MULTIPLE different syndromes. What are 4 ways in which pathogens can cause damage? What factors increase host susceptibility to infection? |
Pathogens may: 1) directly cause tissue damage by elaborating proteolytic enzymes that destroy or damage tissue; 2) induce an excessive immune response resulting in damage [endoxin induces cytokine storm]; 3) cause a hypersensitivity rxn [endocarditis w/immune complex glomerulonephritis]; 4) cause malignant transformation of host cells [hep. B or h. pylori].
Extremes of age, malnutrition, congenital or acquired defects in immunity and various forms of medical treatment can increase host SUSCEPTIBILITY to infection. |
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(MID #45)
What steps are necessary for successful infection to occur? |
1)"Adherance and Colonization." Adherance may be the result of specific (adhesion-receptor) or nonspecific (hydrophobic) interactions. 2)"Evasion of Host Defense." Bacterial capsule can avoid phagocytosis. Bugs may have figured out how to survive intracellularly. Bacteria may express surface receptors mimicking host molecules. 3)"Invasion." Must have the ability to invade tissue or cells. Some spready by elaborating proteolytic enzymes. Others spread by surviving intracellularly and spreading w/host cells to other tissue sites. Invasion may involve subversion of host enzymes or pathways to facilitate survival or spread. 4) "Interference w/the Host Response." Some pathogens mimic or co-opt host defense mechanisms or utilize them to get into tissues. (5) "Host Tissue Damage." Much of the damage resulting from infection is the result of the host immune response rather than the pathogen itself. An example is bacterial meningitis.
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(MID #46)
Discuss VIRULENCE |
Virulence refers to the ability of an organism to cause disease. Dependent on factors such as surface adhesins to enable microorganism to colonize host tissue, toxins that can cause cellular damage, or capsules that interfere w/phagocytosis. Virulence determinants may be found on the chromosome, on a plasmid, or on a bacteriophage. Transmissible from strain to strain or species to species. Genes for different virulence factors may be genetically linked. Antimicrobial resistance may be included as a virulence determinant.
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(MID #47)
What is Falkow's molecular equivalent for Koch's postulates for pathogenicity? |
1)Property under study should be found in the pathogenic members of the species; 2)Inactivation of the gene is associated with decreased virulence; 3)Reversion of the gene restores the pathogen's virulence.
Pili found on E. coli are examples of virulence genes that confer thea bility to certain strains to cause UTIs because of their ability to adhere to uroepithelial cells. |
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(MID #48)
Genetic Variation in Bacteria: Discuss vertical transmission and natural selection with regard to random mutations and subclone survival/proliferation. |
When a bacterial cell divides, the 2 daughter cells are usually indistinguishable. Occasionally a spontaneous genetic change occurs in one of the cells (MUTATION) which is heritable and passed on to the progeny of the variant cell to produce a SUBCLONE w/characteristics different from the original WT parent. This is called VERTICAL INHERITANCE. If the change is detrimental to cell growth, the subclone will be quickly overrun by the healthy, WT population. If, however, the change is beneficial, the subclone may overtake the WT population, illustrating the manner in which evolution is directed by NATURAL SELECTION.
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(MID #49)
What are the two classes of spontaneous mutations that can occur in a bacterial colony to produce subclones? |
POINT MUTATATIONS [change of a single nucleotide] and DNA REARRANGEMENT [via insertions, deletions, inversions, or changes in structure]. Both types of mutations occur at a low frequency (once in 10^6 or 10^8 cells for any particular gene) and lead to continuous, slow evolution of bacterial populations.
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(MID #50)
Discuss HORIZONTAL transmission with regard to bacterial variation. |
Consider bacterium B and bacterium A, each from a different population. THere are 3 mechanisms for transferring a trait from B to A: (1) TRANFORMATION [release and uptake of naked DNA]; (2) TRANSDUCTION [packaging and transfer of bacterial DNA by viruses]; and (3) CONJUGATION [bacterial mating in which cells must be in contact]. For all 3 processes, transferred DNA must be stably incorporated into the genetic material of the recipient bacterium, by (1) RECOMBINATION [integration of the transferred DNA into the bacterial chromosome]; or (2) ESTABLISHMENT OF A PLASMID [transferred material forms a minichromosome capable fo autonomous replication].
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(MID #51)
Why is it desirable for us in the laboratory that bacteria have a haploid genome? What impact does this have in nature? |
Most bacterial cells only contain a single chromosome so each gene is present in only one copy. Genetic changes consequently have an immediate effect on the phenotype or properties of the bacterial cell. Helps us isolate mutants in the lab. Bacterial cells produce colonies on solid media so we can physically separate and identify mutant clones of bacteria. Short generation time and ability to produce large #s of progeny make it possible to isolate virtually any kind of mutation. In nature, these properties mean that EVOLUTION is RAPID!
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(MID #53)
What are the possible consequences of point mutations in bacterial DNA? |
If a point mutation occurs in a coding region, it may alter an aa in a polypeptide, resulting in inactivation/lower activity OR enhanced/new activity. Might be deleterious or beneficial, in other words. In non-coding regions, point mutations can affect signals for gene expression and regulation [a gene from one species may not be expressed in another species b/c of differences in promoters, ribosome bindin gsites, codon usage, etc.]. Spontaneous single nucleotide changes can result in generation of a functional gene.
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(MID #54)
What can cause point mutations in bacterial DNA? |
Point mutations may occur spontaneously through errors in gene replication. May be induced by environmental MUTAGENS that act directly on DNA. Chemicals that damage DNA can induce mutation indirectly. When the amt of damage is considerable, repair genes that are normally repressed become active (SOS Response). One of the induced genes causes a reduction in the proofreading of DNA polymerase and leads to an increase in mutation. This may have evolved as a mechanism for HYPEREVOLUTION to increase the possibility of generating mutants that can survive in a dangerous environment.
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(MID #55)
Discuss Insertion Sequence(IS) Elements |
IS elements are active sequences of DNA w/the ability to jump into other regions of the chromosome. Different bacteria have different numbers and types of IS repeats. Usually 700-3000 bp in length, have inverted repeat sequences at their ends, and encode 1 or 2 proteins responsible for translocating the element to a new location. Transposition is spontaneous. Low target specificity and can insert anywhere. After insertion of the IS in a new location, copy may be left behind in the original position (REPLICATIVE TRANSPOSITION) or the original copy may be excised and transported to a new location (CONSERVATIVE TRANSPOSITION).
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(MID #56)
What effects do IS elements have on gene expression? How might IS elements facilitate spread of antibiotic resistance genes? |
Insertion of an IS element into a gene destroys that gene and can have drastic consequences for expression of genes in the same transcriptional unit. Some IS elements carry promoters and can activate a quiescent gene in a single step. Movement of IS elements is usually associated w/formation of large deletions, inversions, and generation of small circular DNA molecules. Rearrangements can provide the raw materials for new genes or operons. Particularly important for the spread of antibiotic resistance genes is the ability to 2 identical IS elements flanking a gene to move that gene to another position in the chromosome or any other DNA molecule in the cell (called a COMPOSITE TRANSPOSON). The spontaneous and random formation of transposable genes and their subsequent insertion into plasmids or bacteriophages generate the potential for rapid dissemination of these genes to other bacteria.
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(MID #52)
Discuss bacterial TRANSFORMATION |
Uptake of naked DNA molecules and their stable maintenance in bacteria. Griffith demonstrated this in 1928 when he showed that injected into mice a mixture of heat killed virulent (smooth) S. pneumoniae w/ a live attenuated (rough) strain led to development of a live virulent strain which ultimately killed the mouse. Transformable organisms take up DNA when they are in a COMPETENT state. Certain signals trigger the expression of proteins that enable cells to bind and take up DNA. In nature, the DNA to be taken up is released into the environment by the lysis of bacterial cells. Transformation is the least efficient method of gene transfer b/c naked DNA is sensitive to nucleases in the environment.
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(MID #57)
How is the DNA fragment stably incorporated into the bacterial genome once it is taken up by the cells? HOMOLOGOUS RECOMBINATION!!What is the key protein for homologous recombination in bacteria? |
Homologous recombination refers to the fact that two molecules of nearly identical sequence can readily exchange segments. The key protein is "RecA". Several molecules of RecA bind ssDNA and allow it to search another dsDNA molecules for closely related sequences. If an homologous region is found, RecA promotes precise alignment of the moecules which is followed by breakage and rejoining of the individual strands. Homologous recombination depends completely on RecA protein and does not occur in RecA- mutants.
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(MID #58)
What would result in a DELETION-SUBSTITUTION of DNA permitting incorporation of a new gene not previously found in a bacterial chromosome (such as an antiobotic resistance gene)? |
Sometimes homology can only be found in distinct small segments of the incoming DNA. The two crossovers would result in a deletion substitution,: the chromosomal DNA between the crossovers would be replaced by an unrelated piece of the incoming DNA. This permits incorporation of a new gene into the chromosome.
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(MID #59)
Neisseria gonorrhoeae and Neisseria meningitidis are Gram negative, non-motile diplococci that prefer to grow aerobically in an atmosphere slightly enriched with CO2. They exist ONLY in the human host - there is NO other reservoir. Untreated infections can be extremely severe. How do the gonococci FIRST establish an infection? |
First the gonococci attach to mucosal epithelial cells via pili (composed of protein subunit called pilin & possibly other accessory molecules). Pili allow tight binding of bacteria to non-ciliated mucosal cells of the urethra or vagina. Prevents gonococci from being washed away by vaginal discharge or urine. Inhibit phagocytosis by neutrophils. Pili are essential for virulence. Infection is NOT established in human volunteers inoculated with pili- mutatns of N. gonorrhoeae.
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(MID #60)
How does "Opa" or "PII" enable Neisseria gonorrhoeae to colonize a host? |
Opa (PII) is a set of cell surface proteins, or adhesins. These proteins promote adherence of gonococci to each other to form aggregates and confer resistance to the bactericidal activity of serum. Specific Opa proteins enable gonococci to enter epithelial cells in a vacuole. Once inside, the bacteria multiply and are transported to the base of the non-ciliated cells where they are released by "reverse-phagocytosis" into the subepithelial connective tissue. There the organisms continue to multiply, causing tissue damage and sometimes entering the bloodstream.
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(MID #61)
How does Neisseria Gonorrhoeae evade the immune response? |
Gonococci secrete an IgA protease which cleaves the heavy chain of the IgA1 isotype and inactivates it. The gonococci can also switch the pilin proteins on or off (PHASE VARIATION) and can express different antigenic forms of the pilin proteins (ANTIGENIC VARIATION). A single clone of N. gonorrhoeae can give rise to variants expressing pili antigenically distinct from the original clone, arising at a high frequency in the population (10^-4).
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(MID #62)
How do Neisseria gonorrhoeae vary pilin expression to generate antigenic diversity and avoid the host immune response? |
There are 10 or more copies of pilin-related genes in the Neisseria chromosome, generated by gene duplication or point mutations. Only one of these genes is expressed. The expression locus is called "pilE". Nonexpressed loci are scattered around the chromosome and are called "pilS1, pilS2,etc." Only the pilE locus has a promoter and the complete gene including the conserved aminoterminal coding region for pilin. The silent loci have no promoter and are missing coding sequences for the aminoterminal domain. When a Neisseria clone expresses a different pilin, all or part of a pilS gene replaces the homologous region of the pilE gene, generating a new variant. There is a theoretical probability of 10^4 different pilin proteins. Some cassettes result in formation of a pilin gene whose product is processed differently and can't form pili - these have a Pil- phenotype (PHASE VARIATION). Since the presence of pili discourages phagocytosis, the Pil-forms are probably most impt for the invasive stage of gonococcal infection.
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(MID #63)
What should we remember about pili, Opa and antigenic variation in Neisseria Gonorrhoeae? |
Pili are impt virulance determinants of gonococci, impt for initial attachment. Opa adhesion is impt for tight binding and invasion of mucosal epithelial cells. Opa also undergoes antigenic variation. Antigenic variation has 2 impt consequences: 1)Helps the organism survive the immune response, since Abs to one form of pilin or Opa protein are not effective against another form. 2)Stochastic variation allows for selection of attachment proteins that are most effective for a particular tissue. Invasion of cultured epithelial cell lines selects for bacteria that attach better. Different proteins enhance invasion of other cell lines. Variation may give the bacterial population added flexibility.
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(MID #64)
What are BACTERIOPHAGES? |
Viruses are molecules of nucleic acid wrapped in a protein coat. Viruses that infect bacteria are called bacteriophages. Medically relevant because they can mediate the efficient transfer of genes between bacteria, including genes for antibiotic resistance and toxins. Some bacteriophages can convert harmless bacteria into pathogens. The nucleic acid can be DNA or RNA. All bacteriphages have the same life cycle. Infect bacteria, subvert cell's machinery to replicate themselves, lyse the cell to release hundreds of new bacteriophage particles into the environment (LYTIC CYCLE). If a single bacteriophage particle is added to a densely seeded culture of sensitive bacteria on a solid medium, replication of the bacteriophage and lysis of the cells will produce a zone of clearing known as a PLAQUE.
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(MID #65)
Describe TEMPERATE BACTERIOPHAGES |
In addition to the lytic cycle, temperate bacteriophages have an alternative strategy for replication, called LYSOGENY. These bacteriophages produce repressors that turn off their lytic genes for replication, production of heads and tails, and lysis. The bacteriophaeg DNA becomes a benign molecule that coexists with the chromosome known as a PROPHAGE. The DNA can form a circle and integrate into the bacterial chromosome. The integrated form is replicated passively as part of the bacterial chromosome. The lysogenic state is REVERSIBLE. When the repressor is inactivated, the phage DNA is induced to excise from the chromosome and commence the lytic cycle, resulting in lysis of the cell and the release of newly synthesized bacteriophage particles.
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(MID #66)
What is GENERALIZED TRANSDUCTION? |
Occurs as a result of the lytic cycle. While packaging bacteriophage DNA, the head structures of some bacteriophages will package random fragments of the bacterial host chromosome. When these inject their DNA into bacteria, the lytic cycle will repeat and new bacteriophage particles will be produced. A small fraction of these will contain fragments of the bacterial chromosome in place of bacteriophage DNA. When one of these particles injects its DNA into the cell, the cell is not killed. The newly introduced DNA contains only bacterial genes and is free to recombine with the chromosome. B/c the bacterial fragments packaged are random, virtually any bacterial gene of the bacterial chromosome can be transduced. Entire plasmids can be transduced by phages. Some plasmids (those encoding antibiotic resistance in Staphylococci) have evolved signals to allow efficient packaging by phage particles and subsequent transfer by transduction. Another element in the Staphylococcus chromosome which codes for toxic shock toxin senses the peresence of an infecting phage, excises, replicates, and is efficiently packaged.
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(MID #67)
Transducing particles like bacteriophage particles are stable in the environment and can store antibiotic resistance genes for a long time after the original bacterial cell was lysed in order to transduce a new bacterial cell with resistance. Why is this important? |
Take Home Point: Generalized transduction by bacteriophages of bacterial DNA is a significant mechanism of gene transfer of antiobiotic resistence genes in nature.
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(MID #68)
What is SPECIALIZED TRANSDUCTION? |
Requires a temperate bacteriophage. Bacterial gene becomes associated with the bacteriophage genome by recombination. When phage lysogenizes a new bacterial host it brings the associated bacterial gene with it. Since it is a bacterial gene its expression is not turned off by the bacteriophage repressor that inhibits expression of the lytic functions.
Alterations of the properties of a bacterial cell by lysogeny with a temperate bacteriophage is called LYSOGENIC CONVERSION. This occurs in Cornybacterium diphtheriae, which has a b phage that carries diphtheria toxin. Cells of C. diphtheriae that are non-lysogenic for the bacteriophage are incapable of causing diphtheria. Many other examples exist. |
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(MID #69)
Discuss PLASMIDS |
Plasmids are small, double-stranded DNA molecules that are maintained in the cell in addition to the bacterial chromosome. They are usually circular. Encode a variety of genes that confer competitive advantage in certain environments. A variety of pathogenecity factors (toxins, lysins, adhesins for attachment to specific cells, iron scavenging systems, resistance to complement, ability to invade tissue cells) are encoded by plasmids. Successful in nature because of their ability to promote efficient transfer between bacteria by conjugation.
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(MID #70)
How do plasmids guarantee their replication and survival in the cell? |
Plasmid-encoded genes are responsible for initiating replication at least once before cell division so both daughter cells contain the plasmid. For most plasmids, the initiator gene codes for a protein that triggers DNA replication at a specific sequence (origin of replication). Once the origin is activated, the host cell DNA polymerase replicates the plasmid. A simple circuit is required to provide all the functions necessary to initiate and control plasmid replication, known as the REPLICON of the plasmid. For multi copy plasmids, odds are high that each daughter cell will get at least one copy of the plasmid. For low copy paslmids, plasmid-encoded proteins called PARTITION FUNCTIONS bind to the plasmids, assemble them into pairs, attach to the bacterial cell, and ensure that when the bacterial cell divides, each daughter cell receives one plasmid.
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(MID #71)
Discuss SELF-TRANSMISSIBLE and MOBILIZABLE PLASMIDS with regard to transfer of plasmids between bacterial cells by conjugation. |
Self-transmissible plasmids encode all the genes necessary to promote cell-to-cell contact and transfer of DNA. Mobilizable plasmids do not promote conjugation but can be efficiently transferred when present in a cell that contains a self-transmissible paslmid. Self-transmissible plasmids code for proteins required for bacterial cells to form a mating pair, develop a small pore, and transfer plasmid DNA through the pore from one cell to another. An example is the F plasmid which encodes a long tubular structure called the SEX PILUS.
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(MID #72)
Discuss the SEX PILUS encoded on the F plasmid of E. coli and its involvement in bacterial conjugation. |
The F plasmid has 1/3 devoted to transfer genes. Encode a long tubular structure, the sex pilus, which extrudes from the cell. When it contacts a cell that does not have the F-plasmid, it attaches to its surface. The sex pilus depolymerizes, draws the two cells together, and creates a small pore that fuses the cells. One strand of F-plasmid is nicked at an origin of transfer sequence. The nicked single-strand is unwound from the F-plasmid and threated through the conjugation pore to the recipient cell. In the donor cell, the transferred single strand of DNA is replaced by synthesis of a new one. Once the single strand of DNA has been transferred to the recipient cell, a complementary strand is synthesized. When an F+ donor cell mates with an F- recipient cell, the result is two F+ cells. Conjugation is very efficient.
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(MID #73)
How do MOBILIZABLE plasmids replicate? |
They tag along behind self-transferring plasmids. Once the mating pair and conjugation pore have been established by proteins encoded by the self-transmissable plasmid, the mobilizable plasmid proteins deliver it to the conjugation pore and nick a single strand of the mobilizable plasmid at its origin of transfer. The single strand is transferred and the complementary strands are synthesized.
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(MID #74)
The F plasmid can integrate into the bacterial chromosome to form a cointegrate. When it transfers to the recipient cell, the F plasmid also transfers the bacterial chromosome. Thus, it is possible for self-transmissible plasmids to transfer chromosomal genes from one bacterial cell to another. What are these donor cells called and what is the result of this type of gene transfer? |
The donor cells are called Hfr cells because they transfer chromosomal markers at high frequency. Because the chromosome is so large, it takes 100 minutes to transfer it exactly. It is difficult for mating pairs to remain intact that long, so a completely chromosome is rarely transferred. Nevertheless, the bacterial genes closest to the integrated plasmid are transferred with high efficiency. Hfr matings do NOT result in transfer of the complete F plasmid to the recipient cell. The resultant cell is neither F+ nor Hfr.
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(MID #75)
Discuss F' (F-prime) plasmids and their method of bacterial gene transfer. |
If the integrated F plasmid in an Hfr cell excises by recombination, it sometimes excises along with adjacent bacterial genes. The transfer of bacterial genes to the self-transmissible plasmid allows those genes to be efficiently transferred to other bacteria. Since the genes are attached to a plasmid replicon, they need not recombine with the chromosome in the bacterial cell in order to be maintained. POTENT mechanism for bacteria to share genetic info.
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(MID #76)
Discuss bacterial resistance to Quinolones. |
Quinolones inhibit bacterial DNA gyrases (II and IV) and block DNA replication. Resistance to quinolones can be achieved by mutations that alter DNA gyrase to block binding to the quinolones.
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(MID #77)
Discuss R-plasmids and their clinical significance with regard to gene transfer between bacteria. |
R-plasmids are highly transmissible plasmids that carry resistance genes for several antibiotics. They are responsible for rapid dissemination of antibiotic resistance to a wide variety of bacteria. These plasmids can transfer to pathogenic bacteria (Shigella) and also to non-pathogenic enteric bacteria like E.coli. As a result, a member of the normal flora could harbor antibiotic resistance genes and pass them to a pathogen after infection. Since the R-plasmid encoded resistance to multiple antiobiotics, in a single step, a recipient cell can acquire all the resistances. A plasmid was found in India encoding resistance to tetracycline, streptomycin, sulfonamides, chloramphenicol, kanamycin, spectinomycin, trimethoprim, gentamicin, and ampicillin.
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(MID #78)
Discuss transposable antibiotic resistance genes. How is it that antibiotic resistance genes get into plasmids? What is the selective pressure for multiple resistance? |
Antiobiotic resistance genes can be TRANSPOSABLE ELEMENTS. A kanamycin resistance gene was found that was flanked by two identical IS elements and could jump to a bacteriophage and then to another plasmid. Any gene can be transposed to a new location if it is flanked by identical IS elements. A more highly evolved transposon is Tn3, which encodes ampicillin resistance. It appears similar to an IS element with the Ap gene within it. Transposes at a high frequency!
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(MID #79)
What is the role of plasmids and transposable elements in the spread of antiobiotic resistance and pathogenicity determinants? |
Since plasmids move freely among bacteria, they are targets for transposons. Once an antiobiotic resistance gene has been acquired by a plasmid, that plasmid has a selective advantage. Its host will survive treatment with that antiobiotic and the population will thrive, providing more opportunity for spread of the plasmid and acquisition of additional transposons. Enormous selective advantage is conferred to a plasmid with multiple antiobiotic resistance genes.
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(MID #80)
What is an INTEGRON? |
An INTEGRON is a highly specialized gene cassette capturing device. It encodes a specialized recombination enzyme that inserts DNA into a specific site located downstream of a transcriptional promoter. The integron can capture antibiotic resistance and other genes and put them into position so that they are all expressed in tandem from the same promoter. Some integrons contain doens of genes, many of which are antibiotic resistance genes. The integrons can also be incorporated into a transposon so that a large array of genes can transpose in a single event to a conjugative plasmid. Allows rapid spread of multiple antibiotic resistance among bacteria.
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(MID #81)
Discuss transposable antibiotic resistance genes. How is it that antibiotic resistance genes get into plasmids? What is the selective pressure for multiple resistance? |
Antiobiotic resistance genes can be TRANSPOSABLE ELEMENTS. A kanamycin resistance gene was found that was flanked by two identical IS elements and could jump to a bacteriophage and then to another plasmid. Any gene can be transposed to a new location if it is flanked by identical IS elements. A more highly evolved transposon is Tn3, which encodes ampicillin resistance. It appears similar to an IS element with the Ap gene within it. Transposes at a high frequency!
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(MID #82)
What is a PATHOGENICITY ISLAND? (Form of Genomic Island) |
Some genes that are not antibiotic resistance genes may become transposable by flanking IS elements and jump to a plasmid already encoding multiple antiobiotic resistance. Because these genes transposed to the plasmid, the same sets of genes can be integrated into the chromosome. If these genes provide a strong survival advantage, they become permanently incorporated into the chromosome by eliminating plasmid replication genes and elements involved in recombination. They are additions to the basic chromosome. Islands that contain genes for pathogenicity are called "pathogenicity islands."
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(MID #83)
Why are antiobiotic resistance plasmids so common? |
Thousands of tons of antiobiotics are used worldwide each year for medical and agricultural purposes. Enormous selective pressure for resistant bacteria and their resident plasmids.
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(MID #84)
How can we reduce the number of antibiotic resistant strains/plasmids? |
Prevent or reduce unnecessary use of antibiotics. Once selective pressure is reduced, sensitive bacteria begin to reappear because they are not at a disadvantage. Stop use of antibiotics in animal feed. R-plasmids present in animal flora can appear in human pathogens. Rotate use of antibiotics in hospitals to periodically remove selective pressure for resistance to specific antibiotics.
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(MID #85)
Let's talk STAPHYLOCOCCI: General Description |
Family Micrococcaceae. Extracellular, pyogenic pathogens. Induce abscess formation. Nonmotile. Grow in clusters. Extremely hardy and can survive for prolong time periods on environmental surfaces. Family includes Staphylococcus aureus, epidermidis, and saprophyticus.
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(MID #86)
How does one ID Staphylococcus Aureus in the laboratory? |
Gram positive cocci in grape-like clusters. Form round beta-hemolytic colonies on agar. The colonies are gold in color. All staphylococci are catalase positive. The coagulase and manifold fermentation test are used to distinguish S. aureus from other staphylococcal species.
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(MID #87)
Let's talk Staph aureus...STRUCTURAL COMPONENTS |
Cell wall is alternating units of N-acetylglucosamine and N-acetyl muramic acid. Also lipoteichoic acid and surface proteins that facilitate bacterial adherance to host cell surfaces, facilitating attachment to molecules in the host ECM (like fibronectin, fibrinogen, and collagen). Combo of peptidoglycan and lipoteichoic acid are responsible for inducing the sepsis syndrome.
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(MID #88)
What enzymes and toxins are secreted by STAPH AUREUS? |
CATALASE converts hydrogen peroxide to water and oxygen. COAGULASE converts fibrinogen to fibrin and is used to distinguish S. aureus from the other staphylococcal species. HYALURONIDASES hydrolye hyaluroic acids and contribute to tissue breakdown/spread of Staph across tissue barriers. BETA-LACTAMASES can hydrolye the beta-lactam ring of penicillins and cephalosporins rendering the antiobiotics useless.
Toxins produced by Staph Aureus include the superantigen family including TOXIC SHOCK SYNDROME TOXIN-1 (TSST-1), enterotoxins, and the epidermolytic toxins. Membrane damaging toxins including leukocidin and ALPHA TOXIN are also produced. Leukocidin has been associated with soft tissue infections. ALPHA TOXIN may play a role in producing the sepsis syndrome. |
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(MID #89)
Discuss the EPIDEMIOLOGY of Staph infections. |
Humans are the natural reservoir. Coagulase negative staph are part of the normal skin flora and are found in the anterior nares (colonized by S. aureus in 20-40% of the population). Carriage is increased in dialysis patients, diabetics, and HIV-infected subjects. Staph cause infection as a result of autoinoculation or by transmission from a carrier to a patient. Staph are among the most common causes of community and nosocomial infections.
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(MID #90)
What is the PATHOGENESIS of INVASIVE Staphylococcal disease? |
INVASIVE INFECTIONS: Staphylococci cause disease as a result of a mechanical breach in the skin or mucosal barriers OR by the elaboration of toxins. S. aureus are unlikely to cause local or systemic disease in the absence of trauma. Persist as commensals on the skin. Frequently cause prosthetic device (intravascular catheters) related infections. Establishment of infection requires adherence, colonization, invasion, spread, as well as the host response to this process. The staphylococcal proteins (fibronectin-binding or collagen-binding protein) facilitate attachment to host tissue surfaces. After adherence, staph elaborate enzymes that provide nutrients for the bacteria and facilitate bacterial spread to adjacent tissue as well as spread to other organs. Staph can spread to other tissues establish metastatic foci of infection. The primary host response to staph infection is the PMN. Patients w/ defects in PMNs are at increased risk of staph infection.
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(MID #91)
Discuss STAPHYLOCOCCAL TOXIN-RELATED diseases. |
Staphylococci can cause disease via toxins, including food poisoning, toxic shock syndrome (TSS) and scalded skin syndrome. May occur in the absence of a site of infection. TSS is a superantigen-mediated disease. The superantigens are T cell mitogens. Disease is due to thea bility of these toxins to bind APCs MHC 2 molecule outside the peptide groove. Superantigens then bind T cells via the variable region resulting in massive T cell activation and the release of large quantities of cytokines - a "cytokine storm" including IL-1, IL-2, TNF, and IFN-gamma. Result is a multiorgan disease similar in clinical presentation to septic shock w/ significant morbidity and mortality. TSS is caused by a 22kDa protein or one of the structurally related enterotoxins.
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(MID #92)
What diseases are caused by S. aureus? |
Local skin and soft tissue infections, invasive systemic infections such as infective endocarditis, sepsis, or metastatic infections and respiratory tract infections such as pneumonia. Also toxin-related illnesses that include food poisoning or TSS.
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(MID #93)
How do we treat and prevent Staph infections? |
Rx: Antibiotic therapy selected based on antiobiotic susceptibility testing. Staph have gotten increasingly resistant to beta-lactam antibiotics and are less susceptible to 2nd line agents such as vancomycin. Staph abscesses require surgical drainage.
PREVENTION: Topical application of antibiotics to the nares to eliminate nasal carriage of staph in high-risk groups such as hemodialysis patients. Vaccines are in the pipeline, have been tested on animals but not yet on humans. |
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(MID #94)
Coagulase Negative STAPHYLOCCI |
Staph epidermidis is the most common coag neg staph encountered in clinical infections. Less virulent than S. aureus. Encountered in association w/prosthetic devices. Adhere to prosthetic material and establish infection due to elaboration of extracellular polysaccharide (slime or biofilm). Common cause of intravascular catheter, prosthetic valve, and prosthetic hip infections. Resistant to a lot of antiobiotics so treatment requires use of 2nd or 3rd line agents and removal of the prosthetic device. Also frequent contaminants when isolated from blood or body fluids b/c they are part of the normal skin flora and so it's hard to determine whether they are the true pathogens or just contaminating the sample.
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(MID #95)
How do the "flesh eating bacteria" cause disease? |
Group A streptococci, which cause strep throats and rapidly progressing necrotizing fasciitis, are "flesh eating bacteria." They cause damage by making toxins that destroy host tissue. Group A strep can also elicit host immune response that targets heart & kidney tissues, due to cross-reactive epitopes.
TAKE HOME POINT: Most bacteria produce disease both by producing toxins that destroy tissues, block protein synthesis or impair normal cell physiology as well as by activating a host immune response. Often it is the INTENSITY of the HOST RESPONSE to the organism that causes significant disease and even death, as opposed to simple local tissue destruction. Bacteria cause damage both by direct effects on host cells and by evoking the immune system to cause damage. |
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(MID #96)
Distinguish between COMMENSAL FLORA and pathogens. |
Lots of bacteria in the GI tract that are 'normal or commensal flora.' E.coli is an example. Colonizes the gut in the normal host, does not cause any clinical symptoms. Can acquire virulence genes and start symptomatic infection. Can cause major illness (sepsis) if they get into a normally sterile space like the bloodstream, and activate a systemic immune response. E.coli can also acquire virulence genes through genetic processes (conjugation: mating via a sex pilus & exchanging genetic material; or through infection w/ a phage that encodes genes involved in the pathogenesis of infection.)
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(MID #97)
How does normal gut flora E.coli acquire virulence genes? |
Conjugation: mating via sex pilus & exchanging genetic material; Infection w/a phage that encodes genes involved in the pathogenesis of infection including genes to facilitate attachment to a mucosal surface, toxin, or antibiotic resistance genes. This chunk of DNA is called a pathogenicity island and may be incorporated into the genome. Virulence genes may also remain separate on a plasmid. Once in a mammalian host, selective pressure enables the bacteria that reproduce most efficiently to predominate and favors retention of the pathogenicity island or virulence plasmid.
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(MID #98)
How do E.coli cause mucosal (UTI) infections? |
UTIs: due to intro of E.coli into the bladder. Organisms must express adhesins to cause infections. Adhesins encode fimbriae or pili that bind to specific carbohydrate receptors on the surface of bladder mucosal cells. Host must express appropriate carbohydrates to act as receptors for the organisms. When there enough attached bacteria, specific bacterial components elicit an immune response. Flagella activate bladder epithelial cells which respond by producing chemokines that recruit PMNs to the infection site. The production of elastase and superoxide from the WBCs is noxious to the mucosal surface and causes more inflammation. The host must be susceptible by displaying the specific carbohydrate receptors that enable the bacteria to attach and stimulate inflammation.
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(MID #99)
How do E.coli cause diarrheal disease? |
E. coli are common causes of traveler's diarrhea to lethal epidemics affecting marginally neourished infants and children in areas in which clean water is unavailable and fecal-oral contamination occurs. E.coli mediated illness also involves outbreaks of disease due to contaminated undercooked hamburgers. Beef was contaminated by bovine feces which contained E.coli associated with hemolytic uremic syndrome. These organisms produce a specific toxin that causes platelet clumping and targets the glomeruli of the kidney resulting in renal failure.
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(MID #100)
How does E.coli cause fluid secretion in the gut? |
Genes associated w/type III secretion system. Organism constructs a syringe, an apparatus to inject proteins into the host cell, expresses an adhesin, intimin, a tube to facilitate the injection, and squirts in its own receptor (the tir gene product) into host gut mucosal cells. The host cell is taken over (specific proteins are phosphorylated by bacterial kinases, the actin cytoskeleton is rearranged, and a characteristic lesion is formed.) The infected gut epithelial cell, which is normally an absorptive cell, secretes fluids, causing diarrhea.
In traveler's diarrhea a toxin that acts like cholera toxin causes Cl- and H2O secretion. This is an ADP ribosylating enyme which activates adenylyl cyclase and causes water secretion. |
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(MID #101)
How does E.coli cause hemolytic uremic syndrome? |
Organisms must express a pilus adhesin to attach to the gut mucosa. After "loose" pilin-mediated attachment, type III secretion is stimulated enabling the injection of cytotoxin into the cells. Enters the circulation, targets platelets and the glomerulus, causes hemolysis and renal failure.
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(MID #102)
How do E.coli cause sepsis? |
Contamination of the bloodstream w/bacteria following a perforated viscus (such as diverticulitis) or a ruptured appendix. Ordinary E.coli, coated with LPS, activates immune cells to produce cytokines. An exuberant immune response can cause death. However, not all hosts respond as exuberantly to LPS, depending on polymorphisms in their TLRs, etc. Lipid A is the immunostimulatory element. O side chains affect susceptibility of the organism to host defenses such as antimicrobial peptides in the gut.
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(MID #103)
Discuss OPPORTUNISTIC INFECTIONS with Pseudomonas aeruginosa. |
Does not normally cause infection in normal hosts. Immunocompromised patients are at increased risk for pulmonary infection due to P. aeruginosa. It is an exceptionally versatile organism, can grow using minimal carbon sources and is capable of adapting to a wide range of clinical settings. P. aeruginosa has a large genome with metabolic flexibility. It has multiple redundant systems that enable it to adapt to its environment.
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(MID #104)
How does P. aeruginosa colonize immunocompromised patients? |
Organism living in a sink or puddle must be introduced to airways of a susceptible host and rapidly accommodate to this setting. Accomplished by expressing flagella to chemotax and swim toward carbon sources, producing hemolysins, proteases, and phospholipases to break down tissue components, as well as destroying immune cells and Ab. Iron is critical for survival -> siderophores are produced to efficiently get iron from sequestered supplies in the host.
Many genes must be turned on at once. Also, flagella act as ligands for immune cell mediated clearance and cells NOT expressing flagella may predominate in the airway after the initial colonization phase that necessitated motile bacteria. |
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(MID #105)
How does P. aeruginosa adapt to the host environment? |
May express exotoxin A (a potent ADP ribosylating enzyme), exoenzyme S (a type III secreted protein that targets the actin cytoskeleton and opens TJs in epithelial cells), a leucocidin that bores holes in cytoplasmic membranes of WBCs, etc. In a CF lung a different repertoire is activated.
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(MID #106)
Discuss QUORUM SENSING by P. aeruginosa. |
As the bacteria grow, small highly diffusable molecules are secreted. One quorum sensing system is a small homoserine lactone. When homoserine lactone concentrations are sufficient, these quorum sensors diffuse back into any adjacent bacteria, where along with specific translational activators, they regulate gene expression. The same genes will be activated in the entire bacterial community. Genes controlled by quorum sensing systems include exopolysaccharides that form bacterial slime, the surface carbohydrates that coat intravascular catheters and the lungs of patients with CF. Organisms within the biofilm have distinct metabolic requirements, may be anaerobic and less susceptible to antibiotics. There are inherent antibiotic resistance genes activated in this modality of growth. LPS expressed by organisms in biofilm-mode is modified in structure, which affects its immunogenicity.
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(MID# 107)
Let's talk STREPTOCOCCI: General Description |
Streptococcus includes >30 Gram positive species w/spherical or ovoid shape and a tendency to grow in pairs and chains. Non-motile, non spore-forming, (mostly) facultatively anaerobic. Impt pathogens include S.pyogenes (group A strep), Strep agalactiae (group B strep), and Strep pneumoniae (pneumococcus).
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(MID# 108)
Discuss sites of colonization and common sites of infection of Strep pneumoniae, Strep pyogenes, Strep agalactiae, Viridans streptococcus, and Enterococcus faecalis & faecium. (NOTE: Enterococcus is now considered a separate genus) |
S. pneumoniae colonizes the oropharynx and nose. Commonly infects the lungs, sinuses, middle ear, and meninges.
Strep pyogenes colonizes the nares, pharynx, and rectum. Commonly infects the pharynx, skin, and soft tissue. Enterococcus faecalis and faecium colonizes the GI tract and infects the urinary tract, biliary tract, peritoneum, and heart valves. S. agalactiae commonly colonizes the genitourinary tract and commonly infects neonatal, bloodstream, lung & meninges, and genitourinary tract. Viridans streptococcus colonizes the oropharynx and commonly infects dental caries, heart valves, and the bloodstream. |
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(MID #109)
Which of the following bacteria is susceptible to optochin on an optochin disk test? S.pneumoniae, S.pyogenes, E.faecalis, E.faecium, S.agalactiae, and Viridans streptococcus |
S. pneumoniae is susceptible to an optochin disk.
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(MID #110)
Which of the following bacteria is susceptible to a bacitracin disk? (The rest are resistant.) S.pneumoniae, S.pyogenes, E.faecalis, E.faecium, S.agalactiae, and Viridans streptococcus. |
S. pyogenes is susceptible to a Bacitracin disk test.
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(MID #111)
Which of the following bacteria is able to grow in 6.5% NaCl and can hydrolyze bile-esculin? S. pneumoniae, S.pyogenes, E.faecalis, E. faecium, S.agalactiae, and Viridans streptococcus |
E. faecalis and E. faecium is able to grow in 6.5% NaCl and hydrolyze Bile-Esculin.
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(MID #112)
Which of the following bacteria has a positive hippurate hydrolysis test? S.pneumoniae, S.pyogenes, E.faecalis, E.faecium, S.agalactiae, or Viridans streptococcus? |
S. agalactiae has a positive hippurate hydrolysis test.
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(MID #113)
Discuss the Structural Components of Group A Strep (S. pyogenes) |
Outer surface of GAS is a HYALURONIC ACID CAPSULE that interferes w/phagocytosis. Cell wall consists of alternating molecules of N-acetyl glucosamine & N-acetyl muramic acid, carbohydrate antigens, lipoteichoic acid, and proteins that extend to the cellular surface and are involved in adherence and invasion. Surface proteins facilitate attachment to molecules found in the ECM and on host cells. M protein is the major virulence factor of GAS - interferes w/phagocytosis. Strains defective in M protein are avirulent, since M protein promotes colonization of tissue surfaces. (M protein may be involved in the pathogenesis of Rheumatic fever.) Protein F1 and lipoteichoic acid mediate GAS binding to fibronectin, a host ECM molecule found on epithelial cell surfaces. Protein G binds to the Fc portion of immunoglobulin.
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(MID #114)
Discuss the Secreted Products of GAS (Group A Strep = S. pyogenes) |
GAS produce STREPTOLYSINS O and S which are responsible for the hemolysis seen on blood agar plates. DNases, hyaluronidases, and streptokinase may contribute to tissue breakdown and pus formation.
GAS produce pyrogenic toxins that can produce superantigen-mediated TSS. Streptococcal pyrogenic exotoxins (SPE A, B, C) are also responsible for Scarlet fever. |
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(MID #115)
Discuss the epidemiology of GAS infections. (GAS = Group A Strep = S. pyogenes) |
Humans are the natural reservoir for GAS. Asymptomatic carriage can occur in the nares, pharynx, or the rectum. Spread of infection occurs by droplets produced by sneezing or coughing or direct contact with secretions. Skin & soft tissue infections are the results of minor trauma to colonized skin or to skin that is inoculated with GAS by hospital personnel.
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(MID #116)
What diseases are caused by GAS (Group A Strep = S. pyogenes)? |
Causes infectious, toxin-mediated, and post-infectious diseases. Infections include pharyngitis, impetigo, erysipelas, puerperal infections, sepsis, and myonecrosis. Toxin-mediated diseases include scarlet fever and streptococcal TSS. The poststreptococcal diseases include glomerulonephritis and rheumatic fever (with an entirely different pathogenic mechanism).
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(MID #117)
Discuss GAS-caused Pharyngitis |
Pharyngitis is the most common of the streptococcal infections. Characterized by fever, lymphadenopathy, swollen, erythematous tonsils often with a visible purulent exudate. Difficult to distinguish from viral pharyngitis. Serologic assays are helpful (anti-streptolysin O = ASO test) in diagnosing recent streptococcal infection. GAS are the most common bacterial infection of the throat in children esp ages 5-15. Capable of causing infections at this site b/c of the ability of GAS to adhere to and be internalized by oropharyngeal epithelial cells. Occurs via specific adhesin-receptor interactions.
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(MID #118)
Discuss Rheumatic Fever |
Nonsupperative sequealae of Group A streptococcal infections. Characterized by carditis, polyarthritis, subcutaneous nodules, chorea and a skin rash called erythemata marginatum. The Jones Criteria are used to diagnose this illness (it is a syndrome).
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(MID #119)
How do you distinguish between a staphylococcal toxic shock syndrome and a GAS streptococcal toxic shock syndrome? |
Streptococcal toxic shock syndromes frequently demonstrate evidence of clinical infection, often severe, whereas in staphylococcal TSS, infection is unusual.
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(MID #120)
How can we treat and prevent infections by GAS (Group A Strep = S.pyogenes)? |
TREATMENT: GAS remains exquisitely sensitive to penicillins. Main reason for treating streptococcal pharyngeal infections is to reduce the chance of poststreptococcal sequelae such as rheumatic fever.
PREVENTION: Working on a vaccine directed against the immunity inducing type-specific epitopes from the terminal region of the M protein, highly conserved regions, or proteins that mediate adherence to pharyngeal epithelial cells. Worry about vaccines is that they will induce a rheumatic fever type illness or that the epitopes selected might induce a superantigen-type rxn. |
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(MID #121)
Let's talk Strep Pneumo!! This pathogen is the most commonly ID'd cause of bacterial pneumonia and is among the most common causes of mortality worldwide. Widespread multidrug resistance is making these infections increasingly problematic. What is pneumococcus's structure? |
ID'd as lancet-shaped diplococci. On blood agar plates they form white to clear colonies. They are the only species that is susceptible to the OPTICHIN disk. Most impt virulence determinant of pneumococci is the polysaccharide capsule. Interferes w/phagocytosis but doesn't elicit an inflamm response. Cell wall (peptidoglycan) helps initiate inflamm response after infection, recruiting PMNs, initiating the coagulation pathway, and inducing cytokine production. Pneumococci are competent and can acquire DNA from the environment (naturally transformable). Responsible for the acquisition of genes conferring antimicrobial resistance.
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(MID# 122)
Discuss the epidemiology of PNEUMOCOCCUS. |
Humans are the natural reservoir for pneumococci. Colonize the nasopharynx. 20-40% of kids may be colonized at any time. Colonization is seasonal b/c of antecedent viral infections. Pneumococcal infection occurs at the extremities of age and in individuals with defects of humoral immunity (hypogammaglobulinemia, multiple myeloma, or sickle cell disease).
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(MID #123)
What diseases are caused by pneumococcus? |
Sinusitis, otitis, bacterial pneumonia, arthritis, septicemia, and meningitis. These infections can be self-limiting or life-threatening. Infection results from aspiration of material from the oropharynx into the lungs. Interference w/normal respiratory clearance mechanisms will increase the risk of infection. Pneumococci can evade phagocytosis. In the alveoli, adhere to type II alveolar cells. Inflammatory response initiated by components of the bacterial cell wall results in accumulation of fluid in the lung, subsequent consolidation, and eventual resolution. Resolution doesn't occur until type specific Ab develops. Individuals develop type-specific immunity to the capsular type causing infection.
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(MID# 124)
Discuss the clinical manifestations of pneumococcal disease. |
PNEUMONIA: Sudden onset of fever, chills, pleuritic chest pain and cough associated with rusty colored sputum. On chest xray the infiltrate is usually lobar. 1/3 of infections are associated with bacteremia. These are the cases that may be complicated by the development of meningitis, arthritis, or endocarditis (the pneumococcus seeds another organ).
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(MID #125)
Discuss treatment and prevention of pneumococcal infection. |
TREATMENT: penicillin for penicillin-susceptible pneumococcal infections. Multidrug resistance has emerged which sometimes necessitates use of less active agents.
PREVENTION: A polyvalent polysaccharide anticapsular vaccine is currently available. It contains antigens of 23 of the most commonly encountered serotypes and has been effective in reducing invasive pneumococcal disease. A new 7-valent protein conjugate vaccine w/efficacy in infants has been recently released. Can be used in infants less than 2 years of age and reduces nasopharyngeal carriage of pneumococcus. |
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(MID #126)
STREPTOCOCCUS AGALACTIAE (GROUP B STREPTOCOCCUS) |
Group B strep cause a narrow band of beta-hemolysis on blood agar plates. Can hydrolyze hippurate, distinguishes them from other streptococci. Most commonly associated w/ infections of the newborn. Newborns are particularly at risk of Group B sepsis or meningitis if their mothers are vaginally colonized with Gp B strep, lack specific-type Ab, and there are prolonged ruptured membranes. These infections are life-threatening and can result in permanent disability to the infant. Chemoprophylaxis w/penicillin is recommended for all pregnant women who are colonized or at risk.
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(MID #127)
VIRIDANS STREPTOCOCCI |
ID'd by alpha hemolysis on blood agar plates. 24 different species. Part of the oropharyngeal flora and some can be found in the GI tract. Avirulent organisms (relatively) but do cause dental caries (S. mutans) and are the most common cause of subacute infective endocarditis.
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(MID #128)
ENTEROCOCCI |
Separate species from streptococci. Gram positive. Grow in white colonies on blood agar plates and are nonhemolytic (gamma hemolysis). Part of the normal GI flora b/c of their resistance to bile salts. Common causes of infective endocarditis and have emerged as impt nosocomial pathogens b/c of their increasing resistance to many microbials.
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(MID #129)
What is INFECTIVE ENDOCARDITIS? |
Bactericidal antibiotics are absolutely necessary b/c local and systemic host defense mechanisms are of limited benefit. Infective endocarditis is an infection of a cardiac valve or the endocardium caused by bacteria, fungi, or chlamydia. Presence of friable, valvular vegetations containing bacteria, fibrin, platelets, and inflammatory cells. Often valvular destruction w/ local intracardiac complications. A chunk of the friable vegetation may break off and embolize. Bacteria may also seed other tissues causing metastatic infections.
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(MID #131)
Discuss the epidemiology of infective endocarditis. |
W/advent of antibiotics, rheumatic heart disease is far less common and atherosclerotic cardiovascular diseases and mitral valve prolapse w/insufficiency have become more common. Patients w/no history of valvular disease are more common (25-30%). IE is a Gram positive bacterial infection (although gram negs and fungi are infrequently isolated). Pathogens: Streptococcus spp. 34%; Enterococcus spp. 6%; Staph aureus 40%; coag neg staph 5%; gram neg aerobic bacilli 6%; fungi 2%; miscellaneous polymicrobial bacteria 3%; culture negative 4%.
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(MID #130)
Addition notes regarding the epidemiology of infective endocarditis w/regard to particular pathogens: Viridans streptococci, Streptococcus bovis, S. aureus, Coag negative staph, culture negative cases, and nosocomial endocarditis. |
1) Viridans streptococci account for 50-70% of cases of subacute endocarditis. 2)Streptococcus bovis has a unique association w/colonic carcinoma. 3) S. aureus accounts for 80% of cases of acute endocarditis and is the predominant pathogen in IV drug use-related and nosocomial endocarditis. 4) Coagulase negative staphyloocci are the major pathogens in prosthetic valve endocarditis. 5) Culture negative cases account for 4%. 6) Nosocomial endocarditis is increasingly common due to the increased number of invasive procedures performed in hospitals.
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(MID #132)
Discuss risk factors for infective endocarditis. |
Antecendent dental, genitourinary, or GI procedures (often quite minor) producing a transient bacteremia. Also: intravenous drug use, invasive medical procedures such as intravenous lines, hemodialysis, or surgical replacement of cardiac valves.
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(MID #133)
Pathogenesis and Pathology of Infective Endocarditis: Transient Bacteremia |
a) Transient Bacteremia: individuals w/preexistent valvular disease are at risk of subacute IE from transient bacteremias. Minor trauma (tooth brushing, oral irrigation devices, urethral catheterization) may be associated w/low grade bacteremia. In acute IE, bacteremia may be from an uninfected focus, from another site of infection, and from direct intravenous injection.
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(MID #134)
Pathogenesis and Pathology of Infective Endocarditis: Site of Bacterial Seeding on the Cardiac Valve |
(1)Nonbacterial thrombus (NBT). In subacute IE bacteria seed sites of previous micro or macroscopic damage, characterized by deposition of a platelet-fibrin thrombus. Form due to mechanical stress or antecedent valvular disease. In acute IE, the NBT may not be necessary, as more virulent organisms can colonize normal cardiac valvular surfaces.
2)Hemodynamic Factors. Presence of high pressure source (left ventricle). High velocity flow through a narrow orifice (insufficient mitral or aortic valve). Low pressure chamber or "sink" beyond the orifice (left atrium or ventricle during diastole). Infected vegetations from endocarditis exist on the low-pressure side of the high pressure narrow orifice system (atrial surface of mitral valve leaflets in mitral insufficiency. Satellite vegetations may develop due to the jet stream from the primary vegetation. |
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(MID #135)
Pathogenesis and Pathology of Infective Endocarditis: Bacterial Factors |
Gram positive bacterial infection. Gram positive bacteria adhere to cardiac valvular surfaces more avidly than gram negs b/c of surface components (adhesins) such as the extracellular polysaccharide (dextran) for strep that mediates bacterial binding to and colonization of valvular surfaces. Other factors include serum resistance of Gram positives and their capacity to interact with platelets.
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(MID #136)
Pathogenesis and Pathology of Infective Endocarditis: Vegetation Formation |
Once bacteria have colonized the valvular surface a vegetation forms. Consists of bacteria encased in a meshwork of platelets and fibrin. Serves as a barrier to host defenses. Not vascularized, has mononuclear cells or PMNs and is not easily sterilized by host factors or antimicrobials.
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(MID #137)
Pathogenesis and Pathology of Infective Endocarditis: Pathology |
Single or multiple lesions. Appearance of vegetations is variable. Destruction of the underlying valve is often present. Greater necrosis and friability of the lesions associated with acute IE. Adjoining structures (chordae tendinae, myocardial abscesses) may also be involved.
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(MID #149)
Clinical Manifestations of Infective Endocarditis: Diagnosis rests on the signs and symptoms of the disease. |
Most clinical manifestations of IE can be explained on the basis of the 4 major pathogenetic processes occurring during the course of the illness: 1)valvular destruction & local intracardiac complications; 2) bland or septic embolization of vegetations to other organs; 3) sustained bacteremia which contributes to metastatic seeding; 4)immunopathologic phenomena. Onset is typically insidious in subacute or abrupt in acute IE. Findings involve virtually any body organ. Systemic findings include fever (85-95%), fatigue, anorexia, general malaise, and weight loss (25%).
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(MID #138)
Clinical Manifestations of Infective Endocarditis: cardiac, bland/septic embolization, continuous bacteremia |
(A) Cardiac: heart murmurs are present in 85-99% of cases in SBE. In acute IE (as seen in IV drug users) a murmur is present in 1/3 involving the aorta or mitral valve and less frequently when the triscuspid is involved. Development of a new regurgitant murmur leads to congestive heart failure in >90% of cases. (B) Bland or Septic Embolization: Major arterial embolization w/subsequent tissue infarction may occur to virtually any organ. [Commonly coronary vessels resulting in MI, kidneys, CNS, or spleen). Usually bland in SBE but may be septic in ABE. With tricuspid valvular ABE, the lung is frequently seeded. (C) Continuous bacteremia results from steady detachment of organisms from the infected vegetation into the bloodstream. Low concentration of organisms in the peripheral blood at all times.
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(MID #139)
Clinical Manifestations of Infective Endocarditis: Immunologic Features and Other Sites of Involvement |
(D) Immunologic Features of IE: Rheumatoid factor (anti-IgG Fc portion IgM Ab) is seen in 50% of patients w/disease for >6 wks. Titer declines w/treatment. Circulating immune complexes and hypocomplementemia are also seen. Sequela: immune complex glomerulonephritis. (E) Other Sites of Involvement: Skin is frequently involved w/petechiae(20-40%), Osler nodes (necrotizing vasculitis of the glomus body), and Janeway lesions. CNS findings include emboli in >1/3 of cases. Rupture of infected cerebral aneurysms (mycotic) may occur.
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(MID #140)
Lab Findings In Infective Endocarditis |
Most impt lab test is the blood culture. In 2/3 of cases, 100% of cultures will be positive. 3 sets of blood cultures result in >95% yield. Antecedent use of antibiotics will reduce the ability to recover organisms.ALSO: anemia present (50-80%), hematuria (30-50%), RBC casts (12%), and hypocomplementemia (5-15%). The erythrocyte sedimentation rate is uniformly elevated & circulating immune complexes are usually detectable.
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(MID #141)
Special Types of Infective Endocarditis: Prosthetic Valve Endocarditis |
Infections following insertion of prosthetic cardiac valves are divided into early (<60 days post surgery) or late (>60 days). Early onset IE occurs in less than 2% of patients. Coag neg staph is the most common species. Mortality is high (40-80%). Therapy requires replacement of the prosthetic valve as well as antibiotics. Late onset in 2-4% of patients. Organisms are related to dental, genitourinary or skin sources. Low virulence streptococci are most common. Clinical manifestation is similar to SBE. Mortality is lower than in early cases and cure is often achieved without replacement of the prosthetic valve.
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(MID #142)
Special Types of Infective Endocarditis: Culture Negative Endocarditis |
Occurs in 4% of cases. Frequency is lower if no antibiotic has been administered. Infectious and non-infectious explanations. (a)infectious: include fastidious organisms which are difficult to culture. include fastidious Gram negs (HACEK group), fungi, nutritionally variant strep, anaerobes, or rickettsiae. Diagnosis is difficult to establish so mortality is higher in this group. (ii) non-infectious: may occur after prolonged illness as a result of immunologic clearance of bacteria from the bloodstream w/ bacterial persistence in the valvular tissue. Mural endocarditis can result from infected pacer wires or thrombi. Marantic (uninfected NBTE) or other diagnoses that can clinically mimic endocarditis such as myxomas must be considered.
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(MID #143)
Treatment of Infective Endocarditis |
Local host defenses are unable to contain the infection so antimicrobial therapy is needed to eliminate all the organisms. (1)Use of bactericidal antimicrobial agents. Agents that are primarily bacteriostatic will lead to disappearance of signs and symptoms but relapse will occur because the vegetation is not sterilized. Infection requires bactericidal antibiotics administered over a prolonged time period. (b)Treatment should be started early, but great urgency for initiation of therapy is limited to cases of acute endocarditis where rapid valve destruction is likely.
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(MID #144)
Prevention and Treatment Outcomes for Infective Endocarditis |
OUTCOME: Mortality is 5-30%.(Used to be uniformly fatal in the preantibiotic era.) Deaths are more common due to congestive heart failure or emboli rather than uncontrolled infection. Worse prognosis w/increased age, culture neg. endocarditis, aortic valve involvement, congestive heart failure (CHF), resistant or virulent organisms or early prosthetic valve endocarditis.
PREVENTION: Transient bacteremias follow dental, genitourinary and GI instrumentation or surgery. Antibiotics can be administered prior to and during the procedure. Directed against normal flora of the area involved that may cause endocarditis. Recommended for patients w/known valvular diseases. Directed against viridans streptococci for upper respiratory tract or dental procedures and against enterococci for GI and GU procedures. |
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(MID #145)
What is a UTI? |
UTI is significant bacteremia in the presence of dysuria (painful urination), increased urinary frequency and urgency, suprapubic discomfort and costovertebral angle tenderness. Common cause of infections, particularly among young, sexually active women. 1 in 3 women will develop a urinary tract infection before the age of 24 years. Infection may involve lower urinary tract or both upper and lower tracts. Cystitis is the term for the syndrome involving dysuria, suprapubic tenderness w/ urinary frequency and urgency. These symptoms can also be related to lower tract inflammation w/o bacterial infection. Can be caused by urethritis (gonorrheal or chlamydial urethritis). Acute pyelonephritis refers to cystitis accompanied by significant bacteremia and acute kidney infection. Characterized by flank pain, fever, dysuria, urinary urgency & frequency.
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(MID #146)
Define: Lower UTI, Upper UTI, Uncomplicated UTI, and Complicated UTI |
LOWER UTI: cystitis, urethritis, protatitis
UPPER UTI: pyelonephritis, intra-renal abscess, perinephric abscesses (usually late complications of pyelonephritis). UNCOMPLICATED UTI: Infection in a structurally and neurologically normal urinary tract. Simple cystitis of short (1-5 day) duration. COMPLICATED UTI: Infection in a urinary tract w/functional or structural abnormalities (indwelling catheters and renal calculi). Cystitis of long duration or hemorrhagic cystitis. |
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(MID #147)
Discuss the epidemiology of UTIs |
Increased risk groups are: neonates, prepubertal girls, young women, older men, individuals w/structural abnormalities of the urinary tract or immunosuppression (diabetes). In neonates, UTIs occur more often in males. Thereafter they occur more frequently in girls and women. When infections occur in preschool boys they are associated w/serious congenital abnormalities. Lack of circumcision predisposes young boys and infants to UTIs.
Bacteriuria is rare in men under age 50. Symptoms of dysuria are usually related to STIs of the urethra or prostate. After age 50 incidence of UTIs in men increases due to prostate disease. 40% of women will experience a symptomatic UTI at some time during their life and many will have recurrent episodes. Pregnant women have 4-10& prevalence of bacteriuria which increases risk of premature delivery, fetal mortality and pyelonephritis in the mom. In hospitalized patients, UTIs account for 50% of hospital-acquired infections and are a major cause of Gram neg. bacteremia and mortality. |
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(MID #148)
Discuss the microbiology of UTIs |
Organisms are aerobic members of the fecal flora. 95% of uncomplicated UTIs are caused by a single organism. Infections among hospitalized patients, patients w/urinary catheters, or individuals w/structural abnormalities of the urinary tract may be polymicrobial.
Most common pathogen: gram neg rods. Escherichia coli causes 80% of acute infections in patients w/o urinary tract abnormalities. Also: Proteus mirabilis and Klebsiella pneumoniae (which colonize the enteric tract). Enterobacter, Serratia, and Pseudomonas are rare in the outpatient population but more frequent in patients w/a complicated UTI. Staphylococcus saprophyticus, a Gram positive coagulase negative staphylococcus, causes 10% of infections among young, sexually active women. In catheterized individuals w/structural abnormalities of the urinary tract, E.coli accounts for only 35% of infections and other Gram neg species are more impt, as are Gram pos organisms like Enterococcus spp. and coagulase negative staph. |
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(MID #150)
What are the 2 routes by which bacteria can invade and spread within the urinary tract? |
(1)HEMATOGENOUS ROUTE: Infection of renal parenchyma by blood-borne organisms occurs in humans. Kidney is site of abscesses in patients w/bacteremia or endocarditis caused by Gram pos organism (S. aureus). Infections of the kidney w/Gram neg bacilli rarely occur by the hematogenous route.
ASCENDING ROUTE: UTIs in women occur when uropathogens from the fecal flora colonize the vaginal introitus and displace the normal flora. Female urethra is short and proximal to the vulvar and perinal areas, making contamination likely. In women with UTIs, urethra is colonized and the pathogen gains entry to the bladder via urethral massage that accompanies sex. Once the bacteria ascend into the bladder, they may multiply and pass up the ureters (esp. if vesicoureteral reflux is present), to the renal parenchyma. |
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(MID #151)
How are UTIs caused in ppl other than young sexually active women? |
Abnormalities of the urinary tract leading to obstruction of urinary flow are a major factor in development of urinary infection. Extra-renal obstruction due to posterior urethral valves in infant boys or urethral strictures in adult men are uncommon but impt to consider. More common is incomplete bladder emptying due to prostatic hyperplasia. Dysfunction of the bladder due to mechanical (prostate, pelvic floor relaxation) or neurological causes contributes to development of UTIs.
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(MID #152)
What are antibacterial host defenses in the urinary tract? |
High urine flow rate, high voiding frequency, bactericidal effects of bladder mucosa, secreted proteins that bind to fimbrial adhesins on the bacterial wall, and the inflammatory process mediated by PMNs and cytokines. Bladder mucopolysaccharides and secretory IgA are urinary inhibitors of bacterial adherence. In men, prostatic secretions help protect against infection. PMNs and cytokines accompanying the inflammatory response are also helpful.
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(MID #153)
What factors predispose young women to urinary tract infections? |
(1)Short urethra; (2)sexual intercourse & lack of post-coital voiding; (3)diaphragm use (manipulation involved in placing it on the cervix may promote bacterial colonization; (4) spermicide use raises vaginal pH and is toxic to the normal flora, esp. the lactobacilli; also increases adherence of E.coli in vaginal epithelial cells.
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(MID #154)
What factors predispose postmenopausal women to urinary tract infections? |
Estrogen deficiency is a risk factor for recurrent UTIs in postmenopausal women b/c of vaginal flora changes. Protective lactobacilli are replaced by E.coli and other uropathogens.
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(MID #155)
What genetic factors predispose women to urinary tract infections? |
Women of P1 blood group have epithelial cell receptors that mediate the attachment of bacteria. 97% of young women with recurrent pyelonephritis are P1 positive (much higher than uninfected controls). Patients w/upper tract disease secondary to ureteral reflux had P1 phenotype frequency similar to that in the general population. Highlights importance of structural changes in UTIs. Urinary obstruction, reflux, or other anatomic changes make it possible for less virulent organisms to produce a UTI.
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(MID #156)
What bacterial factors are involved in UTIs? |
Bacteria w/enhanced adherence to vaginal and periurethral cells would be selected to colonize the anatomic regions adjacent to the urethral orifice.E.coli have filamentous fimbriae which help w/adhesion, most commonly Type 1 and P-fimbriae. Attachment of Type 1 is blocked by mannose (MS-adhesins). P-fimbriae are mannose resistant (MR-adhesins). P-fimbriae augment virulence of uropathogenic E.coli by allowing more efficient spread from intestinal tract to urinary tract (thereby causing ascending infection). Once in the urinary tract, P-fimbriated strains adhere, persist, and invade the kidney, inducing bacteremia and resulting in pyelonephritis.
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(MID #157)
Discuss P-fimbriated and Type 1 fimbriated bacteria and their susceptibility to phagocytosis in UTIs. |
Type 1 fimbriae increase susceptibility to PMN phagocytosis. P-fimbriae block phagocytosis. Idea of dual-phasekinetics of bacterial adherence in the pathogenesis of UTI. After entry into the bladder, MS-adhesins present on enterobacteriaceae facilitate attachment to the bladder epithelium. When the bacteria ascend to the renal parenchyma, they undergo phase variation and don't express type 1 fimbriae which enhance phagocytosis. Instead, in the upper tract they express P-fimbriae, allowing attachment to renal parenchymal cells.
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(MID #158)
Discuss Proteus mirabilitis, Klebsiella, Staphylococcus aureus, Staphylococcus saprophyticus, and their ability to cause UTIs. |
Gram neg bacterial uropathogens (in addition to E.coli) such as Proteus mirabilis and Klebsiella species, have demonstrated ability to adhere to vaginal and periurethral walls, enhancing their pathogenicity. Among gram positive organisms, S. aureus uncommonly causes cystitis and ascending pyelonephritis, whereas Staphylococcus saprophyticus, which adheres better to uroepithelium than S. aureus or S. epidermidis, is a frequent cause of UTIs.
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(MID #159)
Discuss the clinical presentation of UTIs in neonates, children, and adults. |
Neonates and children less than 2 do not complain of dysuria. Fever, emesis, and failure to gain weight are usual symptoms. Children over 3 yrs will complain of burning on urination and lower abdominal pain. Previously toilet-trained kids may develop enuresis. Adults with cystitis have dysuria, suprapubic pain, urinary frequency and urgency. Urine is often cloudy and malodorous and may be bloody. Fever and systemic symptoms are usually absent in lower tract infection. Acute dysuria in adult women can also be due to acute urethritis (chlamydial, gonococcal, or herpetic) or to vaginitis/vaginosis.
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(MID #160)
How do we clinically distinguish between upper UTIs from lower UTIs? |
Systemic symptoms of fever (greater than 101 deg. F), nausea, vomiting, and pain in the costovertebral areas are highly suggestive of upper UTI (pyelonephritis). Frequently accompanied by urinary frequency, urgency, and dysuria. Rigors (shaking chills) may indicate bacteremia. Flank tenderness is frequent and more intense when there is obstructive disease (renal calculi). Severe pain w/radiation to the groin suggests the presence of renal calculus. Pain from an inflamed kidney may be felt in or near the epigastrium and may radiate to one of the lower quadrants. Patients w/urinary-catheter-associated infection are often asymptomatic but may have fever, chills, leukocytosis, etc.
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(MID #161)
How do we diagnose UTI? |
Can only be proven by culture of an adequately collected urine sample. Essential in suspected cases in males, infants, & children. In sexually active young women (in whom STDs are unlikely), typical clinical features of cystitis in the presence of pyuria, hematuria, or bacteriuria are highly suggestive of UTI.
Urine must be processed immediately. If it remains at room temp contaminants will grow into significant numbers. Hematuria and proteinuria indicate that the patient has crossed from an uncomplicated cystitis to a complicated cystitis or an upper tract infection. Presence of pyuria (>10 leukocytes/μl) in a symptomatic individual is indicative of infection. Urine leukocyte esterase test is used to detect pyuria. Rapid indirect method for detecting bacteriuria is the presence of urine nitrite - bacteria reduce nitrate that is normally present in urine. |
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(MID #162)
When should a urine culture be performed to confirm UTI? |
Urine should be cultured in individuals in whom the diagnosis of cystitis is in question (men, who are more likely to have an STD) or in patients with pyelonephritis. Urine should be cultured in children, pregnant women, and individuals w/underlying structural abnormalities of the urinary tract. [In women who present w/acute onset symptoms of lower UTI (frequency, urgency, and dysuria), urine culture is not mandatory; it is more cost-effective to do a leukocyte esterase-nitrate test. If positive, empiric treatment is prescribed. If negative, a urine culture is done and empiric treatment is prescribed.
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(MID #163)
In males, how do you localize the site of infection to urethra, bladder, or prostate for a UTI? |
Four specimens are collected. First few millimeters of voided urine (VB1) represent urethral colonization, a mid-stream specimen (midstream voided bladder, VB2) represents the bladder, kidney, or both. After the bladder has been emptied, a prostatic massage is performed and prostate fluid is collected (expressed prostatic secretion, EPS). A fourth specimen, the first 10 ml of urine after prostate mssage (VB3) is also collected. These last two specimens represent prostatic infection.
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(MID #164)
How is UTI treated? |
Lower UTI in a healthy, young female w/symptoms of recent onset (within 48 hrs) can be treated with a brief course (3 days) of oral antibiotics. All other women with lower UTIs should be given a 5-7 day course. Impt to ID diabetic patients who are at risk for recurrent infections, pyelonephritis, and perinephric abscesses. For acute pyelonephritis, give IV therapy initially until the patient is afebrile, with completion of therapy orally - total duration of therapy 10-14 days. All patients w/pyelonephritis should have a repeat urine culture 5-9 days after completing therapy, since a percentage of patients will have symptomatic or asymptomatic relapse. The repeat urine culture will detect this. These patients should get 2-4 more weeks therapy.
Good drugs: trimethoprim, co-trimoxazole, and floroquinolones are ideal since they are effective orally, achieve good urine concentrations, and don't disturb the anaerobic flora of the gut and vagina. Asymptomatic bacteriuria in a patient w/an indwelling urethral catheter should not be treated since it will select resistant bacteria. Removal of the catheter will eliminate the bacteria, and if organisms are around 48 hrs after catheter removal, a short course of antibiotic therapy is indicated. Acute cystitis in adult men will respond after 7-10 days of treatment. Acute prostatitis will require 6-12 WEEKS to eradicate the offending organism with a 70% cure rate. [Non-bacterial prostatosis is probably caused by chlamydiae or ureaplasmata, and will respond to tetracyclines, erythromycins, or floroquinolones.] |
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(MID #165)
When is CANDIDURIA seen and how should it be treated? |
Seen in catheterized patients who are often asymptomatic. Diabetics may have true candidal UTIs, as may immunocompromised patients. Persistence of candiduria 48-72 hrs after catheter removal, or fever/leukocytosis, suggests that infection is more than asymptomatic and transient colonization. Important to rule out contamination by vaginal candidosis in the asymptomatic patient. Treatment of infections that do not respond to catheter removal is indicated; oral fluconazole or bladder irrigation with amphotericin B have been used successfully.
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(MID #166)
Discuss catheterization in the context of UTIs. |
Urinary catheters are extremely likely to lead to colonization of the bladder and subsequent infection. Bacteria adhere to the catheter surface and contribute to production of a biofilm composed of bacteria, bacterial glycocalyces, host proteins, and urinary salts like apatite and struvite. Bacteria travel beneath this biofilm along the catheter into the bladder. Long-term use of urinary catheters will always result in colonization and infection, about 8-10% per day. If at all possible, a system of intermittent, straight catheterization should be used, especially in patients who cannot void because of neurologic disease. Relieves stasis of urine in the bladder and prevents damage to bladder mucosa that is in contact with the balloon used to retain the indwelling catheter.
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(MID #167)
Discuss the microorganisms of special relevance in sepsis and septic shock. |
Gram Positive Aerobes: S.pneumoniae, S.pyogenes (Gp.A), S.agalactiae (Gp.B), S.aureus.
Gram Negative Aerobes: Neisseria meningitidis, Enterics [E.coli, Klebsiella, Proteus, Enterobacter, Serratia, Citrobacter, Salmonella], Non-enterics [Pseudomonas aeruginosa, Acinetobacter] Anaerobes: Bacteroides fragilis Upper Bacteria: Myobacteria Tuberculosis Viruses: Flavavirus, Coronaviridae Fungi: Candida, Histoplasma, Aspergillus |
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(MID #168)
Distinguish sepsis from septic shock. |
Sepsis is a complex of fever, tachycardia, and tachypnea in association with local or systemic infection. Septic shock describes sepsis with concomitant hypotension and clinical evidence of diminished tissue perfusion. Syndromes may be initiated by direct invasion of host's bloodstream, by the elaboration of exotoxins, or both. Stimulate host cells to initiate a cascade of inflammatory mediators.
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(MID #169)
Discuss the microbial initiation of septic shock. |
Direct invasion and resulting interaction w/critical host cells constitute one major mechanism by which bacteria can cause sepsis and septic shock. Integral components of outer surface of the organisms can stimulate host cells to produce a stereotypic inflammatory response. LPS (endotoxin) in Gram negative bacteria produces the inflammatory and hemodynamic profiles associated sepsis/septic shock. LPS is deep within the intact cell membrane of the Gram neg. bacteria. Interaction w/host tissue occurs during growth phases of the bacteria, during cell lysis by host clearance mechanisms like complement fixation, or during cell lysis after antibiotic action. In Gram pos. bacteria, a peptidoglycan layer outside the cell membrane of Gram positive bacteria as well as non-peptidoglycan polymers (the teichoic acids) stimulate the release of cytokines (TNF and IL-1).
Staph aureus and Group A strep (S.pyogenes) produce exotoxins that can act as superantigens. They are capable of unconventional binding to APCs and to T lymphocytes. Toxins can bind "outside" the antigen-presenting groove of the MHC Class II molecule of the macrophage and bind to a family of T lymphocytes characterized by identical V-beta regions of the TCR. Permits small amts of toxins to stimulate proliferation of large populations of T cells simultaneously, w/resultant production of large quantities of cytokines. |
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(MID #170)
Discuss the pathophysiology of sepsis and septic shock: LPS-LBP-CD14-TLR4 |
On the surface of the endothelial cell, LPB can bind to soluble CD14 (sCD14) complexed to LPS. On the surface of the MΦ a membrane bound CD14 receptor has been IDd which can directly bind the LPS-LBP complex. Signaling occurs through TLR4 w/activation of intracytoplasmic kinases and translocation of NFκB and transcription of TNF and other inflammatory cytokines. TNF is a central mediator of changes in hemostasis and permeability at the microvascular level. May be a primary trigger for an array of immunologic, metabolic and hemodynamic events. IL-1 are the major mediators of FEVER through prostaglandin E2 release in the anterior hypothalamus. Endotoxin also stimulates the release of platelet activating factor (PAF) produced by MFs. PAF stimulates cell adhesion and amplifies the action of cytokines.
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(MID #171)
Discuss the pathophysiology of sepsis and septic shock: clotting cascade activation and vasodilation. |
Endotoxin causes mechanical perturbation of the endothelial cell memebrane, and activates the clotting cascade. DIC may develop, presenting as active bleeding or thrombosis. Consumption of clotting factors can be demonstrated in the laboratory. Activated Factor XII affects the kinin system, results in formation of bradykinin, a POTENT systemic vasodilator. FACTOR XII activation also activates the complement pathway, leading to PMN aggregation via C5a. ROS are produced by PMNs. Complement activation and/or presence of endotoxin result in activation of phospholipase enzymes resulting in release of AA from the cell membrane phospholipids of PMNs and platelets. Metabolites include prostaglandins, thromboxanes, and leukotrienes, which affect microvascular permeability, vasomotor tone, and cell aggregation. Endotoxin also induces release of nitric oxide from endothelial cells (involved in vasodilitation).
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(MID #172)
Discuss changes in intravascular volume and changes in cardiac function in septic shock. |
Early in transition from sepsis to septic shock, effective circulating volume falls (due to early arterial and venous dilation). As microvascular permeability increases, fluid extravasates from the intravascular space into the interstitium, resulting in a further decrease in the circulating volume.
MYOCARDIAL DYSFUNCTION: Biventricular dilitation and reduced ejection fraction. Elevated cardiac output due to vasodilatation and resultant decrease in afterload as well as tachycardia favor forward flow. Compliance is increased (the ventricles become "baggy"). Contractility is decreased. |
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(MID #173)
Discuss ventilation-perfusion mismatch in sepsis and septic shock. |
Agglutination of WBCs and platelets occurs in the pulmonary vasculature, mediated by activation of the complement cascade as well as release of eicosanoids (leukotrienes, thromboxanes, prostaglandins). Alter perfusion in the microcirculation. Increases in pulmonary capillary permeability release in an increase in interestitial lung fluid and can disrupt alveolar cell barriers resulting in extravasation of fluid into the alveoli. This may trigger stretch receptors in the lung contributing to an increased respiratory rate and primary respiratory alkalosis. If WBC and platelet aggregation proceed and vessel permeability continues, respiratory distress syndrome may result.
These same alterations in endothelial cell integrity, increases in interstitial water and agglutination of WBCs and platelets occur in other organs as well, resulting in multiorgan system failure, a major cause of the high morbidity and mortality of septic shock. There is tissue injury with the releawse of ROS, amplification of the cycle of eicosanoid production, and activation of the extrinsic coagulation cascade w/formation of microthrombi. |
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(MID #174)
Discuss clinical features of sepsis. |
Fever, shaking chills or rigors. Nausea, emesis and diarrhea may occur. Occasionally symptoms have onset 1-2 hrs after insertion or removal of a bladder catheter or after exploration of an infected wound. BP is maintained in normal or near-normal range. Patient may have high fever or normal temperature. Occasionally patient may be hypothermic. Patient is tachycardic with a rapid "bounding" pulse. Respiratory rate is elevated. Skin may be warm and "flushed." Patient may be agitated or confused. Primary respiratory alkalosis. White cell count may be elevated or strikingly low. Prolongation of prothrombin time and decreased platelets.
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(MID #175)
Discuss clinical features of septic shock (which progresses from sepsis). |
Systolic blood pressure <90 mmHg or a 40 mmHg decrease below the patient's baseline systolic pressure. Patients pulse will be rapid and "thready." Patient is often tachypneic but arterial blood gas may reveal primary metabolic acidosis and hypoxemia. Patient may be confused or somnolent. Skin may still be flushed or may feel cold and clammy. Urine volume will be reduced. Clotting factor measurement is compatible with DIC. Platelet count is decreased. Due to decrease in circulating intravascular volume secondary to arterial and venous dilitation, altered microvascular permeability w/ decreased in RH filling in the setting of increased compliance of the ventricles.
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(MID #176)
Discuss bacterial organisms and septic shock. |
Sepsis/Septic Shock have been produced by all species of aerobic and anaerobic bacteria. Aerobic gram neg bacilli (enterobacteriaceae and pseudomonads). Aerobic Gram positive cocci are now the most common cause of sepsis/septic shock as the result of direct infection (Strep pneumo) or toxin production, or both (S.aureus, Strep pyogenes (GpA). Hospitalized patients are at particular risk as a result of their altered immune defenses as well as the instrumentation and procedures necessary for their care. Institutions w/leukemia services or burn units have lots of Pseudomonas aeruginosa and Enterobacter organisms. Surgical and gynecologic units have lots of Klebsiella and anaerobic Gram neg bacillus Bacteroides fragilis. Serratia marcescens outbreaks can occur on a urological service. Polymicrobial sepsis occurs most often from GI tract sites or skin wounds.
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(MID #177)
Discuss diagnosis and treatment of sepsis/septic shock. |
Once sepsis/septic shock is suspected, patient should be examined to determine a possible origin of infection. Cultures of blood, and sputum [as well as CSF, pleural fluid, ascites fluid, joint fluid, wound, etc.] should be obtained as clinically indicated. Antibiotic therapy should be initiated BEFORE the culture results are available. The initial antibiotic regimen should be modified when culture results become available.
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(MID #178)
Discuss possible causes of septic shock if the infection originated in the skin. What might have precipitated this? |
If the infection originated in the skin, etiologic agents include S.aureus, Coag neg Staph, Cornybacterium jeikeium, Pseudomonas aeruginosa, Acinetobacter. Frequently precipitated by an intravenous catheter.
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(MID #179)
Discuss possible causes of septic shock if the infection originated in the respiratory tract. What might have precipitated this? |
Out of the hospital, patient may have aspirated Strep pneumoniae or Strep pyogenes. In the hospital, the patient may have aspirated Psuedomonas aeruginosa, Serratia, Enterobacter, or Acinetobacter.
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(MID #180)
Discuss possible causes of septic shock if the infection originated in the genitourinary tract. What might have precipitated this? |
E.coli, Klebsiella, Enterobacter, Proteus sp., or Pseudomonas aeruginosa. Should be precipitated by a bladder catheter, ureteral obstruction, or cystoscopy.
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(MID #181)
Discuss possible causes of septic shock if the infection originated in the GI or biliary tract. What might have precipitated this? |
E.coli, Klebsiella, or Enterobacter could have caused the sepsis. Precipitating event could be cholangitis or a biliary stent.
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(MID #182)
Discuss possible causes of septic shock if the infection originated in a bowel abscess. What might have precipitated this? |
Perforation of a bowel abscess could result in septic shock, due to any of the following organisms: E.coli, Klebsiella, Enterobacter, Serratia, Salmonella, or Bacteroides.
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(MID #183)
Discuss possible causes of septic shock if the infection originated in the reproductive system. What might have precipitated this? |
Sepsis can be caused by Streptococcus, E.coli, or Bacteroides. Precipitating events? Post-partum, instrumentation.
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(MID #184)
Discuss treatment of septic shock. |
Antibiotics. Treatment of the local site of infection (by removal of contaminated catheters, drainage of collections of pus, or excision of necrotic tissue). Appropriate support of circulation and ventilation. Monitor central cardiac pressure with pulmonary artery catheteriation. Provide supplemental oxygen EARLY ON, and in some patients, airway intubation and support on a ventilator. Blood pressure support may require dopamine and (if volume replacement is ongoing) NE. Small amts of vasopressin can also help a LOT, resulting in a decrease in NE dosing necessary and hemodynamic stabilization.
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(MID #185)
Discuss the use of corticosteroids to treat septic shock. |
In patients with septic shock with relative adrenal insufficiency, replacmeent therapy with low doses of steroids showed a 10% absolute reduction in mortality (63% vs. 53%). A very small subset of patients develop hemorrhagic and thrombotic injury to their adrenal glands as a result of sepsis-associated coagulopathy (Waterhouse-Friderichsen syndrome). This adrenal injury in some patients is extensive enough to cause acute adrenal insufficiency, which worsens the shock state. Corticosteroids for these patients are life-saving.
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(MID #186)
Discuss the potential role of Activated Protein C to treat septic shock in experimental models. |
Activated Protein C is a component of the anticoagulation system and a potent antithrombotic agent. Activated Protein C demonstrates important anti-inflammatory activity. Inhibits PMN activation. Inhibits LPS induced nuclear translocation of NFκB and TNF alpha production in monocytes. In humans, therapy with activated protein C resulted in a relative risk reduction in mortality of 19.4% and an absolute risk reduction of 6.1%.
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(MID #187)
Discuss clinical outcomes of sepsis/septic shock. |
Sepsis is the leading cause of death in the US. Costs $17 billion dollars in the US. 100,000 patients per year will develop septic shock. Of those with Gram neg sepsis, 50% will develop shock. Mortality is related to immune status of the host. In patients with rapidly fatal underlying disease, mortality due to septic shock was 85%. In patients with ultimately fatal disease (death anticipated in 5 years) the mortality was 45%. In patients with nonfatal diseases, mortality was 10%.
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(MID #188)
Are most cases of acute GI illnesses viral or bacterial? |
Most cases of acute infectious diarrhea are caused by viruses (Rotavirus, Calicivirus, Adenovirus). Only 1-6% of stool cultures in patients w/acute diarrhea are positive for bacterial pathogens. Higher rates of detection have been described in foodborne outbreaks (17%) and in patients with severe or bloody diarrhea (87%).
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(MID #189)
What is diarrhea? Infectious diarrhea? Acute diarrhea? Persistent diarrhea? Chronic diarrhea? |
Diarrhea is an alteration in bowel movements characterized by an increase in the water content, volume, or frequency of stools. A decrease in constancy and an increase in frequency in bowel movements to > 3 stools per day have been used as a definition for epidemiological infections. INFECTIOUS DIARRHEA is due to an infectious etiology. ACUTE DIARRHEA is an episode of diarrhea < 14 days in duration. PERSISTENT DIARRHEA is an episode of diarrhea > 14 days in duration. CHRONIC DIARRHEA is diarrhea that lasts > 30 days in duration.
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(MID #193)
Discuss the MICROBIOLOGY of diarrhea. What are the most commonly isolated bacterial pathogens that cause gastroenteritis in the US? |
The most commonly isolated bacterial pathogens are Campylobacter (42% of isolates), Salmonella (32%), Shigella (19%), and E.coli O157:H7 (7%). Some organisms (Salmonella & Shigella) are always associated w/disease, while others (E.coli) are members of the commensal flora and become pathogenic when they acquire virulence factor genes on plasmids, bacteriophages, or pathogenicity islands.
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(MID #190)
What is the role of the Vibrio species of bacteria in causing diarrhea? |
Vibrio are Gram negative bacilli that grow naturally in estuarine and marine environemnts. Can survive in contaminated waters w/increased salinity & temps (up to 37 degrees C). There are 12 species of Vibrio that have been implicated in human infections [most prominent are Vibrio cholerae, parahaemolyticus, & vulnificus). V. cholerae is the etiologic agent of cholera. V. cholerae O1 and O139 are responsible for causing classic cholera which can occur in epidemics or worldwide pandemics. Cholera is spread by contaminated water and food. Usually occurs in communities with poor sanitation. Person-to-person spread is RARE, a high innoculum is req'd to cause disease. Clinical manifestation of cholera ranges from asymptomatic colonization to severe, rapidly fatal diarrhea that begins 2-3 days after ingestion of the bacilli. Fluid loss from cholera can be profound and result in severe dehydration, metabolic acidosis (bicarbonate loss), hypokalemia (low potassium), and hypovolemic shock. Mortality rate is 60% in untreated patients but less than 1% of those who are promptly treated with replacement of loss fluids and electrolytes. Noncholera vibrios such as Vibrio parahaemolyticus can be transmitted through contaminated shellfish and cause a mild to severe secretory diarrhea.
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(MID #191)
What is the role of Shigella in causing diarrhea? |
Shigella are Gram neg bacilli. 4 recognized species (S.sonnei, S.flexneri, S.dysenteriae, S.boydii). S. sonnei enteritis occurs primarily in industrialized countries. S.flexneri occurs in developing countries. S.dysenteriae results in the most severe infections. S.boydii is infrequently isolated. Humans are the ONLY known reservoir for Shigella. Shigellosis is transmitted by the fecal-oral route, primarily by ppl w/contaminated hands and less commonly through contaminated water or food. B/c only a small inoculum is necessary to establish disease (<200 bacilli), shigellosis spreads rapidly in institutions (daycare or custodial institutions) or communities with poor sanitary standards. Shigella invades and replicates in the cells lining the colonic mucosa resulting in symptoms ranging from a mild gastroenteritis to dysentery (abdominal pain, small and frequent bowel movements, stool with blood or mucus). S.dysenteriae produces an enterotoxin called Shiga Toxin which disrupts protein synthesis and produces endothelial damage.
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(MID #192)
What is the role of Campylobacter in causing diarrhea? |
Campylobacter are small, comma-shaped Gram negative bacilli with microaerophilic growth requirements. 13 species have been associated w/human disease. C.jejuni, C.coli, and C.upsaliensis are the most common causes of Campylobacter gastroenteritis. A variety of animals serve as reservoirs. Humans acquire C.jejuni and C.coli infections through consumption of contaminated poultry, milk, and other foods. C.jejuni produces damage to mucosal surfaces of the small and large intestines through invasion into intestinal cells.
[Note: C.jejuni and C.upsaliensis infection have been rarely associated w/Guillain-Barre syndrome, an autoimmune disorder of the PNS characteried by development of symmetrical weakness. The pathogenesis of this disease is related to antigenic cross-reactivity between oligosaccharides of campylobacter and glycosphingolipids present on neural tissue.] |
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(MID #194)
Discuss the role of Salmonella in causing diarrhea with a focus on S.typhi. |
Salmonella are gram neg. bacilli. Broadly classified into typhoidal species (S.typhi and S.paratyphi) and nontyphpoidal species (S.enteritidis & S.typhimurium). S.typhi & S.paratyphi have no reservoirs other than humans and can cause disease with a very low inoculum. S.typhi produces a febrile illness called typhoid fever. After passing through the intestinal cell lining, S.typhi is engulfed by MΦs, where it is able to replicate and get transported to the liver, spleen, and bone marrow. After 5-21 days, patients experience fever w/headache, malaise, myalgias, and a salmon pink rash on the abdomen. Sepsis and intestinal bleeding may develop.
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(MID #195)
Discuss the role of Salmonella in causing diarrhea with a focus on S.enteritidis. |
S.enteritidis colonizes the GI tract of virtually all animals. A large inoculum is req'd for development of symptomatic disease. Infection in humans usually occurs when contaminated foods are improperly stored (left at room temperature) allowing bacteria to replicate. The infectious dose of S.enteritidis is lower in high risk populations such as the elderly, immunosuppressed, or HIV-infected. S. enteritidis infection is characterized by fever, nausea, vomiting, bloody or non-bloody diarrhea and abdominal cramps.
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(MID #196)
Name six groups of E.coli which cause gastroenteritis. |
E.coli is a Gram negative bacillus and a facultative anaerobe. 6 groups of E.coli cause gastroenteritis: enterotoxigenic (ETEC), enteropathogenic (EPEC), enteroinvasive (EIEC), enterohemorrhagic (EHEC) or Shiga-like toxin producing E.coli (STEC), enteroaggregative (EAEC), and diffusely adherent E.coli (DAEC). Clinical spectrum depends on secreted enterotoxin and plasmid-mediated virulence factors that allow for attachment and invasion of intestinal epithelium. ETEC produces heat-labile and heat-stable enterotoxins which affect the small intestines and cause a secretory diarrhea. EHEC produces cytotoxic Shiga Toxins (Stx-1 and Stx-2) that destroy intestinal villi and cause dysentery. EPEC causes diarrhea by destroying microvilli in the small intestines. EIEC causes bloody diarrhea by causing destruction of epithelial cells in the large intestines. Diseases caused by ETEC and EPEC are seen most commonly in developing countries in infants.
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(MID #197)
Discuss the role of EHEC in causing diarrhea. |
Serotype 0157:H7 of the enterohemorrhagic Shiga-like toxin producing E.coli is responsible for most E.coli associated gastroenteritis in the United States. EHEC disease is most common in the summer. Disease has been attributed to consumption of undercooked ground beef or meat products, water, unpasteurized milk or fruit juice. Clinical presentation ranges from mild, uncomplicated diarrhea to hemorrhagic colitis w/severe abdominal pain, bloody diarrhea, and little or no fever. Hemolytic Uremic Syndrome (HUS), a disorder characterized by acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia, is a complication of EHEC infection (especially with Stx-2 production) that occurs in 10% of infected children under age 10. Death can occur in 3-5% of kids with HUS, and severe neurological and renal sequelae can occur in as many as 30% of patients.
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(MID #198)
Discuss the role of inoculum size in the pathogenesis of bacterial diarrhea. |
Almost all GI pathogens are acquired by the fecal-oral route or ingestion of material contaminated by pathogens from other mammalian GI tracts. Sexual activity is also an established route for fecal-oral transmission. For most organisms, ingestion of a large inoculum (10^5-10^8 organisms) is req'd to cause disease, so growth in food or water is a prerequisite for transmission. The infective dose of Shigella, EHEC, Giardia lamblia, or Entamoeba histolytica is much smaller (10-200 organisms) so secondary cases that occur as a result of person-to-person contact are possible.
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(MID #199)
Discuss the role of adherence in the pathogenesis of bacterial diarrhea. |
Specific cell-surface proteins that allow bacteria to attach to intestinal walls are important virulence determinants. V.cholera adheres to the brush border of small intestinal enterocytes via specific surface adhesins including the toxin-coregulated pilus. Strains of E.coli possess highly specialized adhesins, including colonization factor antigens, aggregative adherence fimbriae, bundle-forming pili, intimin, P pili, and Ipa (invasion plasmid antigen) protein that allow them to adhere to intestinal cells.
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(MID #200)
Discuss the role of enterotoxins in the pathogenesis of bacterial diarrhea. |
Enterotoxins are toxins which disrupt the absorptive/secretory function of intestinal mucosal cells w/o killing the cells or causing structural cell damage. Cholera toxin is an enterotoxin that consists of an A and B subunit. The B subunit binds to ganglioside (GM1) receptors on intestinal epithelial cells. The A subunit is internalized and activates adenylate cyclase which leads to cAMP production, causing the active secretion of sodium, chloride, potassium, bicarbonate, and water out of the cell into the intestinal lumen.
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(MID #201)
Discuss the role of cytotoxins in the pathogenesis of bacterial diarrhea. |
Cytotoxins destroy intestinal mucosal cells and induce an inflammatory response secondary to cellular damage resulting in disruption of fluid/electrolyte transport functions. Shiga toxin is produced by S.dysenteriae. Has one A subunit and 5 B subunits. The B subunit binds to the host cell glycolipid (Gb3) and facilitates transfer of the A subunit into the intestinal epithelial cell. The A subunit disrupts protein synthesis by preventing binding of aminoacyl-transfer RNA to the 60S ribosomal subunit. EHEC strains of E.coli also express a Shiga toxin (Stx-1, Stx-2 or both) that is encoded by lysogenic bacteriophages. Stx-1 is identical to Shiga toxin produced by S.dysenteriae, and Stx-2 has 60% homology. After binding of the B subunit, the A subunit is internalized and binds to the 28S ribosomal ribonucleic acid. Disruption of protein synthesis results in destruction of the intestinal cells and villi, decreasing intestinal absorption.
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(MID #202)
Discuss the role of neurotoxins in the pathogenesis of bacterial diarrhea. |
Neurotoxins are toxins which induce GI symptoms or alterations in GI motility indirectly, by affecting the autonomic nervous system. Bacillus cereus produces 2 enterotoxins: the heat-stable proteolysis-resistant enterotoxin that causes the emetic gastroenteritis and the heat-labile enterotoxin that causes the diarrheal gastroenteritis. Other examples of neurotoxins are Staph aureus enterotoxin and Clostridium botulinum toxin.
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(MID #203)
Discuss the role of tissue invasion in the pathogenesis of inflammatory diarrhea (Dysentery), with a focus on the Type III Secretion System(s). |
Bacterial invasion and destruction of intestinal epithelial cells can result in inflammatory diarrhea or Dysentery. Escherichia, Shigella, and Salmonella have a common effector system for delivering virulence genes into targeted eukaryotic cells, called the type III secretion system. Salmonella uses 2 type III secretion systems, Salmonella Pathogenicity Island-1 and 2 (SPI-1 & SPI-2) to mediate invasion into the intestinal mucosa. After binding to the M cells, the SPI-1 secretion system introduces salmonella-secreted invasion proteins (Sips or Ssps) into the M cells resulting in rearrangement of the host cell actin with subsequent membrane ruffling. The ruffled membranes engulf the Salmonellae. Resistant to the acids of the phagosome. Salmonella replicate within the host cell and spread to adjacent epithelial cells and lymphoid tissue.
Shigella species secrete four proteins (IpaA, IpaB, IpaC, and IpaD) into the MΦ or epithelial cell to induce membrane ruffling. After engulfment of the bacteria, Shigella organisms are able to lyse the phagocytic vacuole and replicate within the host cell cytoplasm. |
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(MID #204)
Discuss the GI tract's defenses against bacterial gastroenteritis. |
(1)GASTRIC ACIDITY is the MOST impt host defense against infectious gastroenteritis. 99.9% of bacteria will be killed within 30 min at normal gastric pH < 4. Neutralization of gastric acidity with antacids & H2-blockers OR medical conditions (achlorhydria or gastric resection) decreases the bacterial inoculum necessary to cause disease by 10,000-fold. Maintenance of normal GI motility prevents adherence of pathogenic organisms. Preservation of normal anaerobic bowel flora decrease risk of infection by competing against pathogens for attachment sites & nutrients, and through production of toxic metabolites. (2)The GI tract's MUCOUS MEMBRANE provides a sophisticated defense system. Goblet cells produce mucus, composed of polysaccharides & proteins, which prevents bacterial adherence. Rapid turnover of mucosal cells which migrate from the intestinal crypts to the tips of the villi also prevents bacterial attachment. TJs between mucosal cells prevent bacterial penetration. Paneth cells (located in the crypts of small & large intestines) produce peptides which are toxic to bacteria.
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(MID #205)
Discuss immune mechanisms involved in fighting bacterial gastroenteritis. |
GALT is comprised of M cells and is associated with underlying clusters of Mφs, B & T cells. Found in the small & large intestine, tonsils, and upper respiratory tract (RT). M cells are part of the mucosal lining that phagocytize bacteria and transport them to underlying Mφs. Mφs produce microbial antigens and present them to T cells which interact w/B cells and stimulate production of IgA. IgA is produced in the submucosal space and secreted into the gut lumen where it binds bacteria, resulting in prevention of adherence to mucosal cells and mediation of phagocytosis. IgA is resistant to GI proteases and can bind bacterial toxins.
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(MID #206)
Discuss the clinical manifestations of water diarrhea. |
Mechanism is noninflammatory, enterotoxin-mediated disruption of water/electrolyte secretion by GI mucosal cells. There is no structural damage to the GI mucosa, no inflammation. The site of infection is the small intestine. Organisms don't penetrate the GI epithelium but remain in the lumen. Stools are high volume and watery. There are no fecal WBCs. There is no fever or leukocytosis. Volume depletion predominates.
Representative organisms are: Vibrio cholerae, Enterotoxigenic Escherichia coli (ETEC), Bacillus cereus, and Clostridium perfringens. |
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(MID #207)
Discuss the clinical manifestations of dysentery or inflammatory diarrhea. |
Inflammatory with cytotoxin-mediated destruction or invasion of mucosal cells. There is destruction of the GI mucosal cells with inflammation on histopathology. The site of infection is the large intestine (organisms actually invade but are generally limited to GI mucosa). Stools are frequent, small volume stools containing blood and mucus. There are PMNs in the stool. There is fever and leukocytosis. Volume less is less prominent.
Representative organisms include: Shigella species, Enterohemorrhagic Escherichia coli (EHEC), Campylobacter jejuni, Salmonella, Clostridium difficile, and Entamoeba histolytica. |
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(MID #208)
Discuss the clinical manifestations of enteric fever. |
Mechanism is invasion beyond the GI mucosa and systemic dissemination. Site of infection is the distal small intestine – site of entry (disseminates systemically). Stools: systemic illness in which GI symptoms may not be very prominent. Are there fecal WBCs? Variable. Systemic signs and symptoms predominate: fever, headache, enlarged liver and spleen.
Representative organisms: Salmonella and Yersinia |
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(MID #209)
Name 3 major clues to the diagnosis of infectious diarrheas. |
(1)incubation period; (2) presence or absence of fever; (3) examination of stool for blood and WBCs. Symptoms that begin within 6 hrs suggest ingestion of preformed toxins, such as Staph aureus or Bacillus cereus enterotoxin. Symptoms that begin between 8-14 hrs after ingestion are typical of ingestion of food contaminated w/Clostridium perfringens, which elaborates a heat-labile enterotoxin that causes watery diarrhea and abdominal cramps without fever. Symptoms that begin more than 14 hrs after ingestion can result from viral or bacterial infection. Presence of fecal leukocytes alone or in combination w/occult blood suggests an inflammatory process with a sensitivity and specificity ranging from 20-90%.
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(MID #210)
What other information is helpful in diagnosing infectious diarrheas besides incubation period, presence/absence of fever, and presence/absence of blood & WBCs in the stool? |
Travel history; foods eaten and whether others who shared the food developed similar symptoms; sick contacts; recent antibiotic exposure; and presence or absence of symptoms such as vomiting or abdominal pain. Organisms that cause traveler's diarrhea vary with location but ETEC is the most common bacterial cause of watery diarrhea. A bunch of causes of bacterial food poisoning (see #211). Day-care centers have high attack rates for bacterial gastroenteritis. Recent antibiotic exposure is a major risk factor for Clostridium difficile colitis. Vomiting is associated with an acute infection with a toxin. Abdominal pain may be most severe in an inflammatory process, although painful abdominal cramps may also develop with electrolyte loss in severe cases of cholera. An appendicitis-like syndrome should prompt a culture for Yersinia enterocolitica. Tenesmus (cramps in the rectum felt after a bowel movement) may be a feature of rectal inflammation caused by Shigella.
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(MID #211)
What food-poisoning causing pathogen(s) are associated with the following vehicles: (a) Undercooked Chicken (b) Eggs (c) Unpasteurized Milk (d) Water (e) Fried Rice (f) Fish: shellfish, sushi (g) Beef, gravy |
(a) Undercooked Chicken: Salmonella or Campylobacter species
(b) Eggs: Salmonella (especially enteritidis) (c) Unpasteurized Milk: Salmonella, Campylobacter, Yersinia species (d) Water: Giardia, Norwalk virus, Campylobacter and Cryptosporidium, Cyclospora (e) Fried Rice: Bacillus cereus (f) Shellfish- Vibrio species, Norwalk virus; Sushi – Campylobacter species (g) Beef, gravy: Salmonella, Campylobacter, EHEC |
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(MID #212)
Discuss diagnosis of gastroenteritis-causing pathogens. |
Most watery (non-inflammatory) diarrheas are self-limited and can be treated w/o determination of specific etiology. All patients w/fever & evidence of dysentery acquired outside of the hospital should have stool cultured for Salmonella, Shigella, & Campylobacter. Yersinia will grow in routine culture but is overlooked unless specified. Isolation of C.jejuni requires incubation @ 42 degrees C in microaerophilic conditions. E.coli O157:H7 can be ID'd in special labs by serotyping or thru detection of the Shiga-like toxin. These organisms are excreted continuously so repeat specimens are not req'd. Selective testing improves yield of stool testing. Fecal specimens from patients w/ diarrhea that develops following 3 days of hospitalization have a low yield when cultured for standard bacterial pathogens (Campylobacter, Salmonella, Shigella, etc.) or examined for ova or parasites. Specimens from patients who have been in the hospital for > 3 days may yield C.difficile toxin in 15-20% of cases. So don't bother to submit fecal specimens for routine stool culture or ova and parasites from patients hospitalized for greater than 3 days (“3-day rule”).
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(MID #213)
Discuss Treatment of Bacterial Gastroenteritis. |
Hydration is KEY. Oral rehydration soln containing H2O, salt & sugar is utilized. Intestinal glucose absorption usually remains intact in diarrheal illnesses. Intestines can absorb water if glucose & salt are present to assist in transport of water from the intestinal lumen. Since most courses are self-limited, antibiotic therapy is usually NOT req'd. Recommended in cases of traveler's diarrhea, in which ETEC are likely causes, and prompt treatment w/floroquinolones can reduce duration of illness from 3-5 days to <1-2 days. Empiric antibiotic therapy for febrile diarrheas in other circumstances does not appear to be warranted. Unproven concern about the increased risk of HUS with antibiotic treatment of EHEC enteritis. In vitro data indicate that certain antimicrobial agents can increase production of Shiga toxin. Animal studies have demonstrated harmful effects of antibiotic treatment of EHEC infections. Also, antibiotics may prolong shedding of non-typhi species of Salmonella. So utilization of empiric antibiotics should only be considered in patients w/ moderate to severe disease, and in the ABSENCE of suspected C. dificile colitis or EHEC infection. Empiric therapy consists of a 3-7 day course of a fluoroquinolone.
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(MID #214)
What three features are most common to infections with anaerobic bacteria? |
Anaerobes are a heterogeneous group of bacteria that colonize the skin and mucosal surfaces. 3 main features are common to anaerobic infections: (1)source of the infecting microorganism is the endogenous flora of the patient's own oropharyngeal, GI, or GU mucosa; (2)alterations of the host's tissues provide suitable conditions for the development of opportunistic anaerobic infections (trauma, hypoxia, etc.); (3)anaerobic infections are generally polymicrobial involving mixtures of several anaerobic and aerobic species acting synergistically to cause damage. [Exception: In Clostridial diseases, specific EXOTOXINS are responsible for clinical effects.]
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(MID #215)
Discuss oxygen tolerance of anaerobic bacteria. |
Anaerobes require anaerobic conditions to initiate and sustain growth, but oxygen tolerance is highly variable. Anaerobe can be defined as a bacterium that fails to grow on the surface of solid media in the presence of room air (10%CO2, 18%O2). STRICT ANAEROBES are unable to grow in the presence of > 0.5% O2, and MODERATE ANAEROBES are capable of growing at 2-8% O2. FACULTATIVE bacteria can grow in the presence and absence of air. MICROAEROPHILIC bacteria grow poorly or not at all in air, but distinctly better in anaerobic conditions. Anaerobes generate energy solely by fermentation. Environments favor to anaerobic growth include the sebaceous glands of the skin, the gingival crevices of the gums, the lymphoidal tissue of the throat, and the lumina of the intestinal and urogenital tracts.
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(MID #216)
Discuss the following pathogenic anaerobes: Peptostreptococcus, Veillonella, Clostridium perfringens, Clostridium tetani, Clostridium botulinum, and Clostridium difficile. |
1)Peptostreptococci are Gram positive cocci. Source is the mouth and intestine. Cause oropharyngeal infections, and brain abscesses. 2) Veillonella are Gram negative cocci, found in the intestine. They are a rare opportunistic pathogen. 3) Clostridium perfringens are Gram positive, spore-forming bacilli that produce three exotoxins: α-toxin, θ-toxin, and enterotoxin. They are found in the intestine and the nevironment and cause cellulitis, myonecrosis, and enteritis. 4) Clostridium tetani are Gram positive, spore-forming bacilli and produce an exotoxin called TETANOSPASMIN. Their source is the environment and they cause tetanus. 5) Clostridium botulinum are Gram positive bacilli that produce the botulinum toxin. They are found in the environment and cause botulism. 6) Clostridium difficile are Gram positive spore-forming bacilli that produce A enterotoxin and B cytotoxin. They are found in the intestine and the environment and produce pseudomembranous colitis.
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(MID #217)
Discuss the following pathogenic anaerobes: Propionibacterium, Actinomyces, Lactobacillus, Bacteroides fragilis, Bacteroides species, Fusobacterium, Prevotella, and Porphyromonas. |
1)Propionibacterium are Gram Positive (GP) bacilli found in the skin. Produce acne. Rare opportunistic pathogen. 2) Actinomyces are GP bacilli found in the upper respiratory tract & intestine. Cause actinomycosis. 3) Lactobacillus are GP bacilli found in the mouth, intestines, and genitourinary tract, and produce a rare bacteremia. 3) Bacteroides fragilis are GN bacilli that have a polysaccharide capsule. Produce enterotoxin. Found in the intestine. Opportunistic pathogens that cause abscesses. 4) Bacteroides species: found in the intestines, are opportunistic, and cause abscesses. 5) Fusobacterium is a GN bacillus found in the mouth and intestines that is opportunistic and causes abscesses. 6) Prevotella is a GN bacillus that has a black pigment. Colonizes the mouth and urogenital tract. It is an opportunistic pathogen. 7) Porphyromonas is a GN bacillus found in the mouth and urogenital tract. It is an opportunistic pathogen.
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(MID #218)
Discuss virulence factors of anaerobic pathogens with a focus on attachment and adhesion. |
Virulence factors generally enable species to elicit the following stages of infection: attachment to target cells (mucosal or epithelial); invasion into the tissue; multiplication at the site of infection and avoidance of elimination by host defense mechanisms; mediation of tissue destruction.
The polysaccharide capsule of Bacteroides fragilis and Prevotella melaninogenical allows these organisms to adhere to peritoneal surfaces more effectively. The pili (fimbriae) allow Bacteroides species and Porphyromonas gingivalis (associated w/periodontal disease in adults) to adhere to epithelial cells more effectively. |
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(MID #219)
Discuss virulence factors of anaerobic pathogens with a focus on invasion. |
Most anaerobes do NOT contain special virulence factors for invasion, so invasion depends on ALTERATION IN HOST TISSUE such as trauma (gunshot, surgery), disease (diverticulosis), or isolated events (aspiration). Host factors such as malignancy or impaired blood supply increase probability that dislodged flora eventually produce an infection. Anaerobes involved are normally found at the site adjacent to the infection. Colonic flora are usually isolated in intra-abdominal abscesses; oropharyngeal anaerobes are most commonly isolated in brain abscesses via cribriform plate to the temporal lobe, and lung abscesses (by aspiration).
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(MID #220)
Discuss ability to survive for brief periods in an oxygenated environment as a virulence factor in anaerobic bacteria. |
Most anaerobes lack the ability to produce catalase and superoxide dismutase, which inactivate hydrogen peroxide and superoxide free radicals (O2-), allowing greater tolerance of oxygen exposure and increasing its chance of survival during displacement. Bacteroides fragilis and other pathogenic anaerobes, are far more likely to have the ability to produce catalase and superoxide dismutase.
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(MID #221)
Discuss how anaerobes establish infection. |
1)Bacteroides fragilis has a polysaccharide capsule that interferes with host opsonization & phagocytosis. Capsule produces abscesses even in the absence of living bacteria. B.fragilis also produces extracellular enzymes (collagenase, fibrinolysin, heparinase, hyaluronidase) that may contribute to the formation of the abscess. 2) The clostridial species have the ability to survive adverse environmental conditions through SPORE FORMATION, which are resistant to heat, desiccation and disinfectants. Can survive for years in the environment and return to the vegetative form when placed in a favorable milieu. 3) Ability of bacteria to create & control a reduced microenvironment helps establish anaerobic infections. Most anaerobic infections are mixed infections, involving two or more anaerobes in combo w/facultative bacteria like E.coli. May synergize one another's growth by lowering the redox potential, provoking growth factor, or inhibiting host defenses under anaerobic conditions (O2 dependent leukocyte bactericidal functions).
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(MID #222)
Discuss the following toxins associated with Clostridium perfringens: α-toxin, θ-toxin, β-toxin, and ENTEROTOXIN. |
(1) α-toxin: Lecithinase (phospholipase C) that lyses RBCs, platelets, and endothelial cells. Increases vascular permeability, resulting in massive hemolysis and bleeding and tissue destruction (myonecrosis).
(2) β-toxin: Necrotizing activity, responsible for lesions in necrotizing enteritis. (3) Θ-toxin: Heat and oxygen labile hemolysin; cytolytic (4) ENTEROTOXIN: Heat-labile, produced during phase transition from vegetative cells to spores and released when cells are lysed. Binds to the brush border membrane of the small intestine and disrupts transport and membrane permeability. |
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(MID #223)
Discuss the following toxins associated with Clostridium tetani: tetanolysin and tetanospasmin |
TETANOLYSIN: oxygen-labile hemolysin of uncertain clinical significance
TETANOSPASMIN: Heat-labile neurotoxin produced during the stationary phase of growth which is released when the cell is lysed. Tetanospasmin is a metalloproteinase that enzymatically degrades a protein req'd for docking of NT vesicles onto presynaptic membranes. Loss of this function blocks release of NTs for inhibitory synapses causing excitatory synaptic activity to be unregulated. Toxin binding is irreversible. |
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(MID #224)
Discuss botulinum toxin, released by Clostridium botulinum. |
Blocks neurotransmission at peripheral cholinergic synapses by preventing release of the neurotransmitter ACh. Binding is irreversible and recovery depends upon regeneration of nerve endings.
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(MID #225)
Discuss Toxin A and Toxin B, produced by Clostridium difficile. |
Toxin A (enterotoxin): Produces chemotaxis of PMNs, induces cytokine production, hypersecretion of fluid, and hemorrhagic necrosis.
Toxin B (cytotoxin): Induces polymerization of actin w/loss of cellular cytoskeleton. |
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(MID #226)
Discuss the clinical features of intra-abdominal infections by anaerobic bacteria. |
Secondary peritonitis and intra-abdominal abscesses begin w/entry of GI flora into the sterile peritoneal cavity thru a defect in the intestinal wall (perforation) as a result of obstruction, infarction, direct trauma (gunshot wound, surgery) or inflammatory processes (inflammatory bowel disease, diverticulitis, appendicitis). Peritonitis is usually polymicrobial. 95% of organisms recovered are anaerobes. Bi-phasic clinical presentation. Initially: generalized peritonitis characterized by fever, diffuse abdominal pain, nausea, vomiting, & a rigid abdomen, which may be followed by the signs/symptoms of shock. 2nd stage is characterized by formation of intra-abdominal abscesses; presentation may be variable depending on modification w/antibiotics. Intra-abdominal abscesses are also usually polymicrobial. 60-70% of cultures recover anaerobes. Most common pathogens: Bacteroides species (usually B. fragilis), followed by anaerobic cocci & Clostridia. Also: E.coli, Klebsiella/Enterobacter, Proteus spp., P.aeruginosa, S.aureus, & enterococci. Treating an abscess requires pus drainage (by incision, needle aspiration, surgical drainage, or catheter drainage) AND antibiotic therapy, which should be directed at the anaerobes (especially B. fragilis) and the Enterobacteriaceae.
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(MID #227)
Discuss Clostridium difficile colitis. |
C.difficile is the most common cause of diarrhea associated w/use of antimicrobials. Infection is endogenous in most ppl but environment can be the source as well (evidenced by hospital outbreaks). Infected patients' hospital rooms can have spores. Alteration of normal gut flora by antimicrobials favors C.difficile by allowing antimicrobial resistant strains to overgrow, and by favoring survival of spore-forming bacteria. Disease occurs if organism proliferates in the colon and produces its toxins: enterotoxin (toxin A) and cytotoxin (toxin B). Toxin A causes disruption of intercellular tight junctions followed by altered membrane permeability & fluid secretion. Toxin B causes destruction of the cellular cytoskeleton. Toxins act synergistically. Diarrhea begins 5-10 days after antibiotic treatment. May be mild and watery, OR bloody and accompanied by abdominal cramping, leukocytosis and fever. Severe cases may be associated w/an intense inflammatory response. Colonic mucosa gets studded w/inflammatory plaques which coalesce into a 'pseudomembrane' composed of fibrin, leukocytes, & necrotic colonic cells.
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(MID #228)
Discuss diagnosis and treatment of C. difficile colitis. |
Diagnosis depends on direct detection of the toxins in the stool. Treatment involves discontinuing the implicated antimicrobial agent and/or treatment w/oral metronidazole or vancomycin. Relapses or re-infections requiring re-treatment occur in 20% of patients b/c only the vegetative forms of C. difficile, and NOT its spores, are killed by antibiotics.
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(MID #229)
Discuss the pathogenesis Clostridial myonecrosis, or “gas gangrene”. |
C. perfringens produces wound & soft tissue infections. Clostridial myonecrosis develops in traumatic wounds w/muscle damage after contamination w/dirt or foreign material containing C. perfringens or another species of histotoxic clostridia (C. histolyticum, C. noyyi, C. septicum, and C. sordellii). Clostridia come from spores in the environment or the patient's own intestinal flora. Low redox potential in a wound favors spore germination and multiplication resulting in production of toxins (α-toxin and θ-toxin) which promotes vascular permeability & edema. Intense pain, sense of heaviness or pressure develops at injury site within 1-4 days after inoculation. Progresses rapidly to extensive muscle necrosis and shock within 2 days of onset.
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(MID #230)
Discuss treatment and prognosis of Clostridial myonecrosis (“Gas gangrene”). |
Macroscopic evaluation of muscle reveals devitalized necrotic tissue w/gas caused by metabolic activity of rapidly dividing bacteria. Microscopic examination reveals many Gram positive bacilli and the absence of inflammatory cells as a result of lysis by clostridial toxins. Lab diagnosis is only confirmatory since treatment must be immediately initiated. Prognosis is poor. Mortality is as high as 40-100%. Myonecrosis must be treated w/surgical debridement & high dose penicillin. Antiserum against alpha-toxin doesn't help. Utility of hyperbaric oxygen treatment is uncertain.
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(MID #231)
Discuss pathogenesis of infection with Clostridium tetani. |
C.tetani is extremely sensitive to O2, but spore formation allows the organism to survive in adverse conditions. Found in soil (esp if treated w/manure) and colonizes GI tracts of many animals. Spores are introduced into wounds contaminated w/soil or foreign bodies. In developing countries, tetanus often develops in newborns when umbilical cord is severed in a non-sterile manner. In an area of low redox potential, such as a necrotic wound, C.tetani multiply locally and elaborate Tetanospasmin. The neurotoxin enters the presynaptic terminal of lower motor neurons (LMNs) and reaches the CNS by exploiting retrograde axonal transport. In the anterior horn of the spinal cord, Tetanospasmin blocks postsynaptic inhibition of spinal motor reflexes resulting in spasmodic contractions of protagonist and antagonist muscles. Duration of time between inoculation and onset of neurological symptoms ranges from a few days to wks depending on distance of primary wound infection to the CNS.
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(MID #232)
Discuss the clinical manifestation and diagnosis of tetanus. |
Most common manifestation is generalized tetanus which involves sustained contraction of the masseter muscles (trismus or lock-jaw) or facial muscles (sardonic smile). Other signs: drooling, sweating, irritability, persistent back spasms. The autonomic nervous system is involved in patients with more severe disease. Localized tetanus involves only the musculature at the site of primary infection. Neonatal tetanus is associated with initial infection of the umbilical stump that becomes generalized. Diagnosis is made on the basis of clinical presentation: microscopic detection of C. tetani is rare. Cultures are usually negative since the organisms are extremely sensitive to oxygen. Neither tetanus toxin or Abs are detectable in the patient.
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(MID #233)
Discuss the treatment of tetanus. |
Treatment requires debridement of the primary wound and treatment with metronidazole to eliminate remaining vegetative bacteria, passive immunization w/human tetanus immunoglobulin to bind free tetanospasmin, and vaccination with tetanus toxoid. Since toxin bound to nerve endings is protected from Abs, the patient must be supported until normal regulation of synaptic transmission is restored.
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(MID #234)
Discuss C. botulinum and its mechanism of action. |
C.botulinum is commonly isolated in SOIL and WATER. 7 botulinum toxins and human disease is associated with types A, B, E, and F. Individual isolates typically produce one toxin. Botulinum toxin consists of a neurotoxin subunit (A or light chain) and one or more non-toxic subunits (B or heavy chain) to protect the neurotoxin from being inactivated by stomach acids. Botulinum toxin is very specific for cholinergic nerves and blocks neurotransmission at peripheral cholinergic synapses by preventing release of ACh.
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(MID #234.5)
Discuss infant botulism. |
Infant botulism is the most common form of botulism in the US, and is caused by the neurotoxin colonizing the infant's GI tract. C. botulinum can survive in the infant's GI tract but not in the adult GI tract. Disease typically affects infants less than 1 year old, especially those exposed to honey. Symptoms are usually nonspecific but progressive disease may develop (w/flaccid paralysis and respiratory arrest).
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(MID #235)
Discuss food-borne botulism. |
Starts 12-36 hrs after ingestion of the toxin. Botulism occurs after ingestion of home-canned products that have not been heated at temperatures sufficient to kill C. botulinum spores. The alkaline conditions provided by canned vegetables and fish support conversion from spore to vegetative state, to multiply and produce toxin. May occur with no change in food taste, color, or odor. Because the toxin is heat labile, food must be ingested un-cooked or inadequately cooked. Initial signs are blurred vision, dry mouth, constipation and abdominal pain. Fever is absent. Bilateral descending weakness of the peripheral muscles develop in patients w/progressive disease (flaccid paralysis), with paralysis of the respiratory muscles the most serious consequence. Since the neurotoxin binds irreversibly, complete recovery is dependent on regeneration of the affected nerve endings and may require months to years.
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(MID #236)
How is clinical diagnosis of botulism confirmed? |
If the organism C. botulinum is isolated (culture of implicated food or feces) or toxin activity is demonstrated (inoculation of blood, intestinal contents or food into mice). Treatment involves intensive supportive measures (mechanical ventilation), elimination of GI carriage of the organism (gastric lavage, metronidazole), and botulinum antitoxin to bind circulating toxin.
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(MID #237)
Discuss general principles to follow when treating patients with STDs. |
Counsel patients at risk for STDs on safer sexual behavior. Condoms are better at preventing infections transmitted by fluids from mucosal surfaces (gonorrhea, chlamydia, HIV) than those transmitted by skin-to-skin contact (HSV, HPV). Spermicides with nonoxynol-9 are associated w/genital lesions which may cause increased risk of HIV infection. STD risk factors include young age (under 24 yrs), multiple sexual partners, history of prior STDs, recent new sexual partner, substance use, and contact w/commercial sex workers. Patients w/one STD frequently have another and should be screened appropriately. All patients being evaluated for STDs should be screened serologically for syphilis and offered HIV testing. Treatment of STDs using single dose regiments are preferable due to improved compliance and ease of administration. Partners of patients w/STDs should be evaluated and when indicated, treated. Asymptomatic persons at risk for STDs should be screened for STDs.
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(MID #238)
Let's talk GONORRHEA: Epidemiology |
Gonorrhea is an acute bacterial infection, transmitted by sexual contact or perinatally. May involve asymptomatic infection, urethritis, cervicitis, pelvic inflammatory disease (PID), & disseminated infections. Etiologic agent is Neisseria gonorrhoeae. Gonorrhea is 2nd only to chlamydia as most commonly reported STD in the US. 15-24 yr olds are at greatest risk. Transmission may occur from infected urethral, cervical, rectal, & pharyngeal surfaces. Incubation period: 1-14 days, but usually 2-5 days. Transmission from M to F after one exposure is 50-70%. Transmission from F to M is 20%. Recurrent infection is common. Gonorrhea is usually spread by carriers who have NO symptoms or who have ignored symptoms. Symptomatic patients have usually been recently infected by such carriers, who must be traced/treated to prevent reinfection. 50% of all women infected have mild or asymptomatic infections. Most men are initially symptomatic. PID due to chlamydia & gonorrhea is a HUGE public health problem leading to infertility & ectopic pregnancy. Gonorrhea & chlamydia are associated w/increased risk of tranmission/infection w/HIV.
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(MID #239)
Let's talk GONORRHEA: Microbiology and Pathogenesis |
N. gonorrhoeae is an aerobic non-motile Gram negative coccus that tends to grow in pairs (diplococci) w/adjacent sides flattened (kidney bean shaped). Forms oxidase-positive colonies. Differentiated from Neisseria meningitidis by its ability to ferment glucose but not maltose. It is a fastidious organism, requiring complex media and a CO2-enriched atmosphere for growth.
Gonococci infect columnar or cuboidal epithelium. Attach to mucosal epithelial cells, penetrate INTO cells and multiply (intracellular infection), and then pass through the cells into the subepithelial space where infection is established. Pili, Porin, and Opa proteins mediate attachment and penetration into host cells. The gonococcal lipooligosaccharide (LOS) stimulates the inflammatory response and release of TNF-alpha which leads to most symptoms associated w/gonococcal disease. Vigorous PMN response leads to sloughing of the epithelium, development of submucosal microabscesses, and exudation of PUS. |
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(MID #240)
Let's talk GONORRHEA: Virulence Factors (PILI) |
PILI: Pili on surface extend thru the peptidoglycan & outer membrane. Composed of repeating protein subunits (pilins). Their expression is controlled by the “pil” gene complex. Pili are responsible for tight binding of the bacteria to nonciliated mucosal cells. Tight binding prevents gonococci from being washed away by vaginal discharge or urine. Pili also inhibit phagocytosis by PMNs. Essential for virulence. Infection was NOT established in human volunteers inoculated w/mutants of N. gonorrhoeae lacking pili.
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(MID #241)
Let's talk GONORRHEA: Virulence Factors (1)Porin Protein (2)Opacity Proteins (Opa) (3)Lipooligosaccharide (LOS) (4)Transferrin-Binding Proteins (5)Beta-Lactamase |
(1) PORIN: The porin protein is the outer membrane protein (OMP) in N. gonorrhoeae which is essential for the organism's survival. Forms pores for nutrients to pass into the cell and wastes to exit. Protein can interfere with PMN degranulation and phagolysosome fusion, protecting the bacteria from the host inflammatory response. Facilitates invasion into epithelial cells and resistance to complement-mediated serum killing. (2) OPACITY PROTEINS (Opa): These cell surface proteins, or adhesins, also mediate tight binding to epithelial cells and are important for cell-to-cell signaling. (3) LOS is an impt cell wall component w/endotoxin activity. (4) Transferrin-binding proteins mediate acquisition of iron for bacterial metabolism by competing w/their human hosts for iron. (This is different from most bacteria that synthesize siderophores to scavenge iron.) (5) Beta-lactamase: some bacterial strains produce beta-lactamases that can degrade penicillin, leading to resistance.
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(MID #242)
Let's talk GONORRHEA: Immune Evasion |
ANTIGENIC VARIATION: N. gonorrhoeae changes its antigens frequently. A single clone can give rise to variants expressing different antigenic forms of pili and Opa proteins, due to multiple copies of pili and opa genes in the Neisseria chromosome. Helps the organism survive the host immune response. Abs specific for one form of pilin or Opa protein are not effective against another form. Each isolate of the gonococcus may have a unique antigen profile allowing the organism to reinfect a host repeatedly.
PHASE VARIATION: Ability to switch production of pilin and Opa proteins on and off. The gonococci also secrete an IgA protease which cleaves and inactivates the heavy chain of the IgA1 isotype. |
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(MID #243)
Let's talk GONORRHEA: Clinical Features |
(1)30% of male and female patients with gonorrhea will be infected with Chlamydia trachomatis. Patients diagnosed with gonorrhea are routinely treated for both pathogens.
(2)Urethritis in men (3)Urogenital infection in women (4)Rectal infection/proctitis in men and women (5)Pharyngeal infection (6)Pelvic inflammatory disease (7)Disseminated gonococcal infection (8)Perinatal disease, leading new newborn conjunctivitis |
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(MID #244)
Let's talk GONORRHEA: Clinical Features Spotlight on Urethritis in men |
URETHRITIS IN MEN: Anterior urethritis is the most common manifestation in men. Presents w/purulent urethral discharge and/or dysuria. Discharge may be profuse, minimal or undetectable. Erythema of the urethral meatus may occur. Initial infection is asymptomatic in 5% of men. Complications include prostatitis, epididymitis (presents w/unilateral testicular pain and swelling), urethral stricture, and disseminated gonococcal infection.
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(MID #245)
Let's talk GONORRHEA: Clinical Features Spotlight on Urogenital Infection in Women |
UROGENITAL INFECTION IN WOMEN: The endocervical canal is the primary site of infection (mucopurulent cervicitis). Urethra may be involved as well (urethritis). Symptoms include vaginal discharge, pelvic pain, dysuria, frequent urination, and abnormal uterine bleeding. The majority of infected women are asymptomatic. Many present for treatment only after referral from a symptomatic male partner. Untreated infection can result in pelvic inflammatory disease and infertility. Other complications include Bartholin's glands abscess or infection (labial pain and swelling), and perihepatitis (Fitz-Hugh-Curtis syndrome involving upper right quadrant abdominal pain and tenderness and elevated liver enzymes; due to direct extension of gonorrhea or chlamydia from the fallopian tube to the liver capsule and overlying peritoneum.
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(MID #246)
Let's talk GONORRHEA: Clinical Features Spotlight on Rectal Infection/Proctatitis |
Can occur in men and women. In men rectal gonorrhea is common among men who have sex with men. In women, rectal infection can occur from contamination of the rectum by infected vaginal secretions or by rectal intercourse. Symptoms include anal irritation, painful defecation, bleeding, cramping, constipation and mucopurulent rectal discharge. Many patients w/rectal infection are asymptomatic.
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(MID #247)
Let's talk GONORRHEA: Clinical Features Spotlight on Pharyngeal Infection |
Results from orogenital contact. Usually asymptomatic but can cause exudative pharyngitis and cervical adenitis, and can be a source of further transmission.
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(MID #248)
Let's talk GONORRHEA: Clinical Features Spotlight on Pelvic Inflammatory Disease |
PID is infection of the endometrium, fallopian tubes, and/or surrounding peritoneum which occurs as a complication of cervicitis, due to ascending infection. 10-20% of women w/gonorrhea develop PID. Often, more than one organism is isolated (Chlamydia, anaerobes). Signs/symptoms include lower abdominal pain, fever, dyspareunia (pain during intercourse) and vaginal bleeding. Signs include mucopurulent endocervical discharge, cervical motion tenderness (pain during movement of the cervix during pelvic exam), uterine or adnexal tenderness, fever, an elevated WBC count, and an elevated erythrocyte sedimentation rate (ESR) or C-reactive protein. Tubo-ovarian abscesses can occur. Tubal scarring can lead to infertility and ectopic pregnancy. Infertility has been ID'd in 1 in 5 women after one episode of PID, and risk rises w/subsequent episodes. Incidence of ectopic pregnancy increases 7-fold w/1 episode of PID.
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(MID #249)
Let's talk GONORRHEA: Clinical Features Spotlight on Disseminated Gonoccocal Infection |
DGI results from gonococcal bacteremia and occurs in 1-3% of infected patients. Symptoms include fever, skin lesions (pustules, sometimes hemorrhagic or necrotic, on an erythematous base, located mostly on the extremities), tenosynovitis (inflammation of the tendon and its enveloping sheath), oligoarthritis (inflammation of a few joints, most commonly knee, also elbows, ankles, wrists, small joints of the hands and feet), and migratory polyarthralgias (joint pain). This presentation is called arthritis-dermatitis syndrome. Untreated, overt septic arthritis in one or two joints can occur. Rarely, hepatitis, endocarditis, or meningitis can occur. Deficiency in the terminal complement components (C5-C8) may increase susceptibility to disseminated infection. Female sex and menstruation are associated w/disseminated infection.
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(MID #250)
Let's talk GONORRHEA: Clinical Features Spotlight on Perinatal Disease |
Neonate may develop gonococcal conjunctivitis (ophthalmia neonatorum) due to passage through an infected birth canal. Presents as a severe sight-threatening bilateral conjunctival inflammation. Administration at birth to all neonates of 1% silver nitrate, 1% tetracycline, or 0.5% erythromycin eye ointments protects against the development of ophthalmia neonatorum.
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(MID #251)
Let's talk GONORRHEA: Diagnosis |
(1)Gram stain of urethral discharge showing intracellular Gram negative displococci is >90% sensitive and >98% specific in symptomatic men for diagnosis of gonococcal urethritis. Gram stain is less reliable in women and asymptomatic men. In these cases diagnosis is confirmed by culture or nucleic acid amplification of affected sites. (2) Cultures of urethral, cervical, rectal and pharyngeal specimens must be inoculated onto selective media (e.g., modified Thayer-Martin medium) to suppress growth of contaminating organisms. Inoculation should also occur onto nonselective media (e.g., chocolate blood agar) because some gonococcal strains are inhibited by the vancomycin present in most selective media. (3) Nucleic acid amplification assays for N. gonorrhoeae have been developed for use w/clinical specimens (urine, urethral, cervical). Assays are highly sensitive and specific. In many labs assays have replaced culture. Combination assays for both N. gonorrhoeae and Chlamydia organisms are available.
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(MID #252)
Let's talk GONORRHEA: Treatment |
3rd generation cephalosporins (a single injection of ceftriaxone or a single oral dose of cefixime) or a quinolone (e.g., single oral dose of ciprofloxacin) are the treatment of choice for uncomplicated gonococcal urethritis or cervicitis. Penicillin was used in the past but not useful at this point due to resistance. Resistance to quinolones has become prevalent in Asia, the Pacific Islands (including Hawaii), California, and among men who have sex with men in some US cities and so is not recommended for treatment in certain settings. Coinfection w/ C. trachomatis often occurs, so presumptive treatment for chlamydia (w/either a single dose of azithromycin or a 1-week course of doxycycline) is appropriate if chlamydial infection is not ruled out. Recent sex partners (within 60 days of onset of symptoms) should be referred for evaluation and treatment for N. gonorrhoeae and C. trachomatis. Treatment of PID is more complicated and prolonged and should include coverage of N. gonorrhoeae, C. trachomatis, anaerobes, Gram negative rods, and streptococci. There is NO vaccine to prevent gonorrhea.
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(MID #253)
Let's talk CHLAMYDIA: Epidemiology |
Chlaymidia trachomatis causes asymptomatic infection as well as urethritis, cervicitis, pelvic inflammatory disease and (certain serovars) lymphogranuloma venereum. Most common sexually transmitted bacterial disease in the US. The majority of ppl who are infected are asymptomatic. Most prevalent in sexually active adolescents.
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(MID #254)
Let's talk CHLAMYDIA: Microbiology |
Obligate intracellular parasites w/inner and outer membranes similar to GN bacteria, but lack a rigid peptidoglycan layer. Replicate within host cells via unique growth cycle involving 2 morphological components: stable elementary body (EB), which can persist in the extracellular environment and is responsible for host-host and cell-cell transmission, and the reticulate body (RB) which replicates inside the cell and cannot survive outside. Cycle starts when small, infectious EB attaches to host epithelial cell and enters cell by endocytosis within a vacuole derived from the host cell membrane. In the cytoplasmic phagosome, phagolysosomal fusion is inhibited. 8 hrs after entering host cell, the EB becomes the metabolically active RB which uses the host cell ATP for its energy requirements. The RB replicates by binary fission and can be detected by histological stains. Phagosome w/accumulated RBs is called an INCLUSION. RBs then reorganize into smaller EBs and 48-72 hrs after infection the cell ruptures and releases the infectious EBs.
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(MID #255)
Let's talk CHLAMYDIA: Pathogenesis |
Clinical features of chlamydia infections are caused by direct destruction of cells during replication as well as the host inflammatory response (infection causes secretion of TNF and IL-6 and infiltration of PMNs). Chlamydiae possess a type III secretion apparatus which serves as a means of transporting chlamydial proteins outside the inclusion membrane, where they may regulate host cell transcription, facilitating key events like inhibition of fusion of the chlamydial inclusion with host cell lysosomes. Infection does not confer long-lasting immunity. Reinfection is frequent and induces a vigorous inflammatory response w/subsequent tissue damage.
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(MID #256)
Let's talk CHLAMYDIA: Clinical Features |
(1)Urethritis in men; (2)Cervicitis and PID; (3)Urethritis in women; (4)Proctitis; (5)Perinatal infection; (6)Lymphogranuloma Venereum (LGV); (7)Specific serologic variants categorized on the basis of antigenic differences in the major outer membrane protein are associated with specific disease. Lymphogranuloma venereum (LGV) is associated with serovars L1 to L3. Endemic trachoma (chronic keratoconjunctivitis endemic in the Middle East, North Africa, and India and is a cause of blindness) is associated with serovars A to C. Most genital tract infections (except LGV) are caused by serotypes D through K.
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(MID #257)
Let's talk CHLAMYDIA: Clinical Features Spotlight on Urethritis in Men |
Incubation period is 7-21 days. Symptoms: dysuria, urethral discharge, urethral itching. Nongonococcal urethritis (NGU) is applied to men w/symptoms or signs of urethritis who do not have gonorrhea. Postgonococcal urethritis (PGU) refers to nongonococcal urethritis which develops 2 wks after treatment of gonococcal urethritis in men. Chlamydia trachomatis causes 50% of NGU and PGU. Other etiologies include Ureaplasma urealyticum, Mycoplasma genitalium, Herpes simplex, and Trichomonas vaginalis. (If a patient is co-infected w/gonorrhea & chlamydia, symptoms of the chlamydial infection may develop after successful treatment of the gonorrhea b/c the incubation period is longer and use of B-lactam antibiotics to treat gonorrhea would be ineffective against C. trachomatis.) Patients w/urethritis frequently have pyuria (WBCs in the urine) & increased leukocytes on Gram stain of a urogenital swab. C. trachomatis urethritis is less severe than gonococcal urethritis but can't distinguish the two on clinical grounds alone. Must test/treat for both. 25% of men w/chlamydial urethritis are asymptomatic. 5-10% of male STD patients have asymptomatic C. trachomatis urethral infection. Complications and other infections in men include epididymitis, prostatitis, proctitis, and Reiter's syndrome (arthritis, conjunctivitis, and urethritis +/- skin lesions).
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(MID #258)
Let's talk CHLAMYDIA: Clinical Features Spotlight on Cervicitis and PID |
Majority of women with cervicitis due to C. trachomatis (as many as 80%) are asymptomatic and have a normal cervical examination, but mucopurulent cervicitis can be seen. Symptoms include pelvic pain, vaginal discharge, abnormal vaginal bleeding, and dysuria. Complications include Bartholinitis (infection of Bartholin's ducts), and pelvic inflammatory disease (PID). PID due to chlamydia and gonorrhea is an enormous public health problem leading to infertility and ectopic pregnancy. Control of PID is complicated by high frequency of asymptomatic cervical infections.
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(MID #259)
Let's talk CHLAMYDIA: Clinical Features Spotlight on Urethritis in Women |
C.trachomatis is one of the etiologic agents in the acute urethral syndrome and a cause of sterile pyuria (WBCs in the urine but negative urine culture). Symptoms of dysuria and urinary frequency can be misdiagnosed as bacterial urinary tract infection. Urethral discharge may be seen and Gram stain of urethral discharge may reveal increased PMNs. Urethritis may occur in the presence or absence of cervicitis.
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(MID #260)
Let's talk CHLAMYDIA: Clinical Features Spotlight on Proctitis |
Can occur in men and women through anal intercourse or, in women, due to spread of secretions from the cervix. Symptoms include anal pruritis and mucopurulent rectal discharge.
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(MID #261)
Let's talk CHLAMYDIA: Clinical Features Spotlight on Perinatal Infection |
Neonatal conjunctivitis involving a copious purulent discharge can develop in infants exposed to C. trachomatis at birth (newborn inclusion conjunctivitis). NOT prevented w/administration at birth of antimicrobial drops, and is treated w/oral erythromycin (a macrolide). Possibility of concomitant chlamydial pneumonia should be considered. NOTE: inclusion conjunctivitis is also seen in adults, often due to autoinoculation w/infected genital secretions.
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(MID #262)
Let's talk CHLAMYDIA: Clinical Features Spotlight on Lymphogranuloma Venereum (LGV) |
Caused by serovars L1, L2, and L3. LGV is endemic in areas of Africa, SE Asia, India, South America, and the Caribbean. Occurs sporadically elsewhere. Ongoing outbreak of LGV proctatitis in men who have sex with men in Europe, Canada, and the US. After incubation period of 3-30 days, a primary lesion (papule or ulcer, usually painless) appears at the site of infection. Days to weeks later, the secondary stage occurs, involving constitutional symptoms such as fever, headache, and myalgias, and inflammation of the lymph nodes draining the site of infection. Inguinal nodes, most commonly involved, can become painful, fluctuant buboes that can enlarge and rupture, forming draining fistulas. Untreated LGV may progress to a chronic ulcerative phase involving lymphatic obstruction, genital elephantiasis, urethral or rectal strictures, and chronic hard inguinal masses. LGV proctitis can be misdiagnosed as Crohn's disease.
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(MID #263)
Let's talk CHLAMYDIA: Diagnosis |
(1)Diagnostic tests should also include tests for N. gonorrhoeae. (2) Nucleic acid amplification tests including PCR, transcription-mediated amplification, & strand displacement amplification, are currently considered the tests of choice for lab diagnosis of genital C. trachomatis infection. Highly sensitive & specific (90-98%). Can be performed on urethral & cervical samples as well as urine & vaginal swabs. Combo assays for both N. gonorrhoeae & Chlamydia organisms are available. (3) C. trachomatis may be isolated in cell culture from urethral & cervical specimens but requires adequate sampling, quick transport, and special cell lines. Culture is not as sensitive as the nucleic acid amplification tests and is NOT routinely used for diagnosis of genital chlamydial infections. (4) Serology is of limited value b/c antibody titers can persist for a long time, and adults often do not produce IgM antibodies. So distinguishing between current and past infections is impossible. Serologic testing IS useful in the diagnosis of LGV.
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(MID #264)
Let's talk CHLAMYDIA: Treatment |
Uncomplicated urethritis or cervicitis should be treated with one dose of azithromycin (a macrolide) or a 7-day course of doxycycline (a tetracycline). LGV should be treated with doxycycline for 21 days. All sex partners within the preceding 60 days should be evaluated and treated.
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(MID #265)
Let's talk CHLAMYDIA: Prevention |
Education re: safer sex practices, prompt treatment of symptomatic patients and their sexual partners, and screening and treatment of at-risk asymptomatic patients. Recommended to screen for C. trachomatis at annual pelvic examination for all sexually active women age 25 or younger, and sexually active women older than 25 years w/risk factors (e.g., more than one sexual partner, a new sex partner). Sexually active men who have sex with men should be screened for chlamydia and gonorrhea at least annually. The sensitivity of the nuclei acid amplification tests performed on urine is nearly identical to sensitivity of more invasive specimens such as urethral swabs and cervical specimens, and availability of this non-invasive screening technique has been shown to improve adherence to screening guidelines. NO VACCINE is currently available.
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(MID #266)
Let's talk HERPES: Epidemiology |
HSV causes ulcerative genital disease, a recurrent, life-long viral infection. HSV types 1 & 2 are DNA viruses that tend to produce latent & recurrent infections. After primary infection the virus remains latent in the DRG for the patient's lifetime - can periodically reactivate causing viral shedding, risk of transmission, and risk of recurrence of symptoms. Genital herpes infections are primarily caused by HSV-2. HSV-1 more frequently causes orolabial lesions (gingivostomatitis) and keratitis, can also cause genital lesions, but recurrent HSV-1 genital lesions are much less frequent. Most ppl infected w/HSV-2 have NOT been diagnosed. Many have mild or unrecognized infections but shed virus intermittently in the genital tract. Transmission to others CAN OCCUR during asymptomatic viral shedding. Most genital herpes infections are transmitted by ppl unaware they have an infection or who are asymptomatic when transmission occurs. 60% of men and women infected with HSV-2 may not have symptomatic outbreaks and may be unaware of their infection. Herpes simplex and all other genital ulcer diseases have been associated w/increased transmission of HIV.
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(MID #267)
Let's talk HERPES: Pathogenesis |
Primary infection w/HSV occurs through mucosal membranes or breaks in the skin. Virus replicates locally in mucoepithelial cells, causing disease at the infection site, and then moves along sensory nerves to the ganglia where it becomes latent. Reactivation occurs w/spread of virus peripherally along sensory nerves to the skin sites where a new lesion develops w/inflammatory response.
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(MID #268)
Let's talk HERPES: Clinical Features |
During primary HSV infection patients have systemic symptoms including fever, malaise, headache. Local symptoms: pain, itching, dysuria, & vaginal or urethral discharge. Tender inguinal lymphadenopathy develops. Herpes infections are painful fluid-filled vesicles that evolve into pustules and finally to shallow ulcers on an erythematous base. Multiple lesions are common. May erupt in tightly grouped clusters. Lesions can coalesce into large, painful ulcers. In women, primary HSV infection is associated w/recovery of the virus from the cervix in 80% of cases. Lesions range from a severe erosive cervicitis to mild erythema and small herpetic lesions. Duration of primary disease averages 21 days. 5-10% of patients will have aseptic meningitis manifested by nuchal rigidity, headache, photophobia, and CSF lymphocytic pleocytosis. Recurrences of genital herpes after primary infection have been recorded in over 70% of patients followed over 9 months. Clinical manifestations in recurrent disease are different: milder in symptom and shorter in duration. Recurrent lesions are smaller in number and unilateral. 50% of patients experience prodromal symptoms consisting of tingling or pain at the site of eruption which occur 24-48 hrs prior to appearance of lesions.
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(MID #269)
Let's talk HERPES: Complications (including neonatal HSV infection) |
Aseptic meningitis, transverse myelitis, and perinatal transmission. HSV infection of the newborn is acquired through contact of the infant with active virus as a result of its passage through the infected birth canal. As a consequence of the immaturity of the infant's immune system, the acquisition of neonatal herpes is associated with dissemination of the disease and organ involvement (e.g., of the spleen, liver, lung and heart). Severe neurologoical damage may occur. Disease localized to the skin or eye has been reported. Risk of neonatal HSV infection is greatest in a woman who develops primary genital herpes near term. Most specialists recommend that women with active genital HSV lesions at the onset of labor deliver by caesarean section to protect the baby from infection.
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(MID #270)
Let's talk HERPES: Diagnosis |
Diagnosis can be confirmed via viral culture, or detection of antigen w/direct fluorescent Ab. Detection of DNA (using in situ hybridization or PCR) is becoming increasingly available. Sensitivity of culture is maximized if the base of the ulcer is scraped and if the test is performed earlier in the course before healing begins. Cytologic detection of cellular changes of herpes virus infection is neither sensitive nor specific in genital lesions and should NOT be relied on for diagnosis of HSV. Serologic tests that differentiate between HSV-1 and HSV-2 can be helpful. Abs develop during first several weeks following infection and persist indefinitely. Not typically used to establish role of HSV as a cause of an acute genital lesion. Can be used to diagnose persons w/unrecognized infection and to manage sex partners of persons with genital herpes. Presence of HSV-2 Ab indicates anogenital infection. Presence of HSV-1 Ab cannot distinguish between anogenital and orolabial infection.
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(MID #271)
Let's talk HERPES: Treatment |
Treatment w/oral acyclovir, famciclovir, or valacyclovir during primary infection can decrease the duration/severity of symptoms but will NOT prevent recurrence of disease. During recurrent disease, treamtent w/same oral meds at lower doses and for shorter duration can be used at onset of symptoms to decrease the time to healing and duration of viral shedding. Use of daily suppressive therapy can be used to reduce recurrences (by 80%) and may be beneficial to patients w/severe or frequent recurrences. Suppressive antiviral therapy reduces but does not eliminate subclinical viral shedding. Daily suppressive therapy with valacyclovir reduces transmission of genital herpes infection among monogamous, heterosexual, HSV-2 serodiscordant couples by approximately 50%. Symptomatic sex partners should be evaluated and treated. Asymptomatic sex partners should be offered type-specific serologic testing to determine whether risk for HSV acquisition exists.
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(MID #272)
Let's talk HERPES: Prevention |
Condoms reduce genital herpes if infected areas are consistently and correctly covered by the condom. Suppressive treatment reduces transmission. HSV vaccines are being tested in clinical trials.
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(MID #273)
Let's talk SYPHILIS |
Syphilis causes a substantial proportion of genital ulcers. Leading agent in the differential diagnosis of HSV. HSV ulcer is painful while the syphilitic chancre is painless. But the two are difficult to differentiate and microbiologic testing to confirm a diagnosis is required. Evaluation of all patients with genital ulcers should include at least a serologic test for syphilis and a diagnostic evaluation for genital herpes, as well as microbiologic tests for other causes of genital ulcer diseases as appropriate. Any patient with genital ulcers should be offered HIV testing. All diseases characterized by genital ulcers have been associated w/increased risk for HIV infection.
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(MID #274)
What is CHANCROID? |
Chancroid is caused by Haemophilus ducreyi. Uncommon in the US. Frequently encountered in Africa. Mostly occurs in men. Major risk factor for HIV transmission b/c of ulcerations. After 2-5 day incubation period a small macule develops then ulcerates. Resulting ulcer, which can occur on the penis or anus in men and the vulva or vagina in women, is markedly painful w/ragged undermined edges and a base covered w/a gray or yellow exudate. Expansive, tender lymph nodes called buboes can occur and become fluctuant, sometimes w/spontaneous drainage. Satellite lesions may develop. Solitary lesion is most common. Diagnosis: culture the organism, see the organisms on aspiration of a lesion (Gram negative slender rods or coccobacilli). Difficult to grow, requires special media. Therapy is with a single dose of Azithromycin (a macrolide), a single injection of Ceftriaxone (a 3rd generation cephalosporin), or a 3-day course of Ciprofloxacin (a quinolone). Sex partners should be examined and treated regardless of whether disease symptoms are present, if they had sexual contact with the patient during the 10 days preceding the patient's onset of symptoms.
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(MID #275)
What is Granuloma Inguinale? |
Genital ulcerative disease caused by Calymmatobacterium granulomatis, a GN bacillus. Uncommon in the US. Endemic in Papua New Guinea and parts of India, southern Africa, the Caribbean, and South America. Disease begins as a small, painless subcutaneous nodule in the genital area which then ulcerates WITHOUT regional lymphadenopathy. Diagnosis is made by demonstration w/Wright's or Giemsa's stain of dark-staining Donovan bodies in a smear of the lesion or histologic study of the tissue involved. Treatment: doxycycline or trimethoprim-sulfamethoxazole for at least 3 weeks.
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(MID #275)
Let's talk HPV: Epidemiology |
Human papillomaviruses are dsDNA viruses that cause anogenital warts (condylomata acuminata) and are associated w/anogenital malignancy including cervical, vaginal, vulvar, penile, and anal carcinoma. HPV is the most common viral STD in the U.S. True prevalence of HPV is unknown because most infections are subclinical, but it's very common among young sexually active women. Spread by unprotective penetrative intercourse and close physical contact involving an infected area. Risk of HPV in women is related to the number of male sex partners and to the male partners' number of female sex partners. HPV infections are usually transient (clear within 2 yrs) and the prevalence of cervical HPV infection falls quickly after age 30. Women w/persistent infection are at highest risk for the development of high grade cervical intraepithelial neoplasia (CIN) and cervical cancer. Men and women w/asymptomatic infection fuel transmission of the virus. Screening for and treatment of cervical dysplasia w/Pap smears has decreased incidence of cervical cancer in the developed world but worldwide cervical cancer is the 2nd most common cancer in women.
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(MID #276)
Let's talk HPV: Microbiology and Pathogenesis |
100 types of HPV. 25 from genital tract. Benign anogenital warts by HPV 6 and 11, “low-risk” for development of neoplasia. Types 16 and 18 are associated w/intraepithelial neoplasia of the cervix, vulva, penis, and anus. Linked unequivocally to cervical cancer. Individual can be infected w/more than 1 type. Several types of cutaneous HPV (types 1&2) cause non-genital cutaneous warts. Persistent infection w/oncogenic HPV increases risk of high-grade intraepithelial neoplasia & cervical cancer. Transient infection poses << risk. HPV infects the epithelium. Can persist in the nucleus extrachromosomally or integrate into the host genome. Viral integration results in overexpression of oncoproteins E6 and E7 which disables 2 major tumor suppressor gene products, the p53 tumor suppressor gene product and the retinoblastoma protein. Enable host cell immortalization.
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(MID #277)
Discuss ANOGENITAL WARTS caused by HPV |
Condylomata acuminata (anogenital warts) can occur on penis, vulva, vagina, cervix, perineum, anus. Flesh- to gray-colored lesions. Single or multiple papules. Vary in size (less than 1 mm to several cms) and can be flat, relatively inconspicuous papules or verrucous, pedunculated, or cauliflower-like masses. May be associated w/burning & itching. Usually asymptomatic. Women w/external genital lesions often have cervical or vaginal involvement. Incubation period is 4-8 wks. Wart may not become apparent for 6 months. Condylomata acuminata need to be distinguished from condylomata lata of secondary syphilis.
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(MID #278)
Discuss ANOGENITAL SQUAMOUS INTRAEPITHELIAL NEOPLASIA caused by HPV |
Strong link between persistence of high-risk HPV types and squamous intraepithelial neoplasia (SIN) of the cervix, anus, vagina, vulva, and penis. Can progress to squamous cell carcinoma of the infected site of left untreated. Cervical HPV infection is the primary worldwide cause of cervical cancer. HPV has also been linked to oropharyngeal cancers.
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(MID #279)
How do you diagnose HPV? |
No cell culture system. Presence of virus in nonkeratinized tissues (cervix) can be assessed by PAP smear or biopsy. Koilocyte is a large squamous cell w/a clear halo around a shrunken nucleus – consistent w/HPV. Diagnosis involves careful external genital exam and a speculum exam (in women) involving a Pap smear for detection of cervical atypia. When appropriate, application of acetic acid to cervix to ID (w/aid of colposcopy) suspicious lesions for biopsy. Screen for anal HPV infection in women and men who engage in receptive anal intercourse.
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(MID #280)
How do you treat genital warts? |
Physical disruption (cautery, excision, freezing, laser), chemical disruption (podophyllotoxin, trichloroacetic acid), or immunomodulation (imiquimod). Treatment may be applied topically or intralesionally.
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(MID #281)
How do you prevent HPV infection? |
Condoms decreases transmission but transmission can occur w/o intercourse (from scrotum to vulva during foreplay). Consistent condom use reduces risk of cervical and vulvovaginal HPV infection in women. Once infected w/HPV, regular Pap smears and follow-up/treatment of abnormal smears is highly effective at preventing developing of cervical cancer. In summer 2006 a vaccine which targets HPV types 6,11,16, and 18 was approved by FDA for use in girls/women ages 9-26 yrs. 100% effective in preventing cervical dysplasia caused by the vaccine HPV types. Should be given to girls when they are 11-12 yrs old. Routine pap smear screening is still necessary b/c the vaccine does not protect against all types of HPV.
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(MID #282)
What is vaginitis? |
Results in vaginal discharge. May present as increas ina mt, odor, or color of vaginal discharge, as well as itching, dysuria, dyspareunia, or vulvar irritation. 3 most common causes are bacterial vaginosis (BV, 40-50% of cases), vulvovaginal candidiasis (20-25%), and trichomoniasis (15-20%). BV and trichomoniasis may be associated w/increased risk of HIV infection. Dx relies on speculum exam & microscopic exam of vaginal discharge. Can be treated w/topical or oral therapy. Specific agent depends on type of vaginitis.
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(MID #283)
What is bacterial vaginosis? |
Clinical syndrome resulting from shift of normal vaginal flora from predominantly lactobacilli to increased numbers of Gardnerella vaginalis, Mobiluncus species and other anaerobes. BV is not sexually transmitted, but sexual activity can increase risk of BV thru changes in vaginal pH. BV is associated w/having multiple sex partners. Routine treatment of sexual partners of women w/BV is NOT recommended. Dx is aided by visualization on microscopic exam of clue cells (vaginal squamous epithelial cells covered w/bacteria), pH of vaginal fluid >4.5, and a fishy odor of discharge before or after addition of 10% KOH (the whiff test).
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(MID #284)
What is vulvovaginal candidiasis? |
Due to excessive growth of fungus Candida (usually Candida albicans). Occurs in setting of recent antibiotics, HIV, poorly controlled diabetes mellitus, and pregnancy. Occurs most frequently in women w/o risk factors. Not acquired sexually. Treatment of sex partners is not recommended. May be considered in women w/recurrent infection. Use of 10% KOH in microscopic evaluation of vaginal discharge improves visualization of the yeast. Vaginal culture can also confirm the diagnosis.
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(MID #285)
What is trichomonal vaginitis? |
Caused by a protozoan, Trichomonas vaginalis. Male partners of women w/trichomonal vaginitis are frequently infected so treatment of sexual partners is routinely recommended. Tiny hemorrhages may be seen on the cervix (strawberry cervix). Diagnosis may be confirmed by visualizing mobile trichomonads on microscopic exam of vaginal discharge. Culture is more sensitive.
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(MID #286)
What is a mercken? |
A pubic wig for women! Syphilis makes your hair fall out.
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(MID #287)
Discuss the etiology of Syphilis. |
Family Spirochaetaceae (Treponema, Borrelia, Leptospira). Treponema pallidum causes syphilis. Slender, tightly coiled, helical. Undulating movement around its center (flexuose) distinguishes it from nonpathogenic treponemes on darkfield microscopy. Cannot be cultured in vitro. Unlike other pathogenic bacteria, genome lacks transposable elements. Genome is highly conserved. There is a paucity of genes involved in the biosynthesis of nutrients or energy production. This bug is a scavenger.
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(MID #288)
Discuss the epidemiology of Syphilis. |
Infectious transmission by sexual contact, congenital, kissing/close contact w/active lesion, transfusion, or accidental injection. Most infectious early in disease: chancre, mucous patch, condyloma latum. Essentially, an immunologically intact person cannot spread the disease sexually after 4 years.
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(MID #289)
Discuss the pathogenesis of Syphilis. |
Start with an initial lesion. There is a systemic spread of treponemes to all organs, including the CNS. The time to clinical lesion appearance (10^7 organisms/mg of tissue) is directly proportional to the size of the inoculum. Stages: (1) Primary: chancre at site of inoculum; (2) Secondary: disseminated disease; (3) Latent (early & late): clinically inactive, dx can only be made by serology; (4) Late (tertiary): clinically apparent or not; vaso vasorum lesions & gummas; (5) Neurosyphilis: can occur at any stage of the disease.
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(MID #290)
Describe the clinical manifestations of Syphilis. |
Incubating syphilis (3-90 days w/ a mean of 3 wks). Ceftriaxone eradicates incubating syphilis. Primary syphilis: chancre. Secondary syphilis: fever, rash, adenopathy, nephritis, condyloma latum. Latent syphilis: asymptomatic, RPR positive. Late syphilis: cardiovascular, gummas. Congenital syphilis.
Neurosyphilis: (a) meningitis; (b) meningovascular/meningoencephalitis syphilis; (c) ocular: Argyll Robertson pupil; (d) tabes dorsalis – demyelination of the posterior column; (e) PARESIS: Personality, Affect, Reflexes, Eyes, Sensorium, Intellect, Speech. |
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(MID #291)
How do you diagnose syphilis? |
Direct examination for spirochetes by darkfield microscopy. Isolation of Treponema pallidum (rabbit testes?) Biopsy. Serologic tests. Nontreponemal reaginic tests: VDRL, RPR. False positives can occur due to rheumatic diseases, hepatitis esp. hep C, and early HIV. Specific treponemal tests: FTA, MHA-TP, TPHA. False positives: Lyme disease. PCR: low sensitivity.
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(MID #292)
How do you treat syphilis? |
(1)Primary syphilis: PCN IM X 1 (penicillin intramuscular injection x 1)
(2)Secondary syphilis: PCN IM X 1 (3)Latent syphilis: early –> PCN IM X 1; late or unknown duration, PCN IM X 3 (4)Late syphilis (tertiary): check if CSF involvement (5)Neurosyphilis: PCN IV + IM? (6)PCN Allergy: desensitization (7)Jarisch-Herxheimer: systemic rxn to release of spirochete antigens (8)Definition of treatment success: follow RPR |
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(MID #293)
Poem about Syphilis: |
Chancre, “acne vulgaris” on his skin from his feet to his head. Hair falling out. Pupils won't close in the light. Heart is cavorting. Squints through his gunbarrel site (tunnel vision). Arthralgia. Aorta needs a plumber. Has tabes dorsalis. Sabershinned babies (babies with congenital syphilis). Gummas. Paresis. Crazy.
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(MID #294)
What is the major risk factor for infection by Rickettsia, Erlichia, or Borrelia? |
Exposure to vector (tick, louse, mite).
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(MID #295)
Discuss pathogenesis of RICKETTSIA |
Fastidious, GN bacteria, which are obligate intracellular pathogens. Vector bites and feeds. Regurgitates bacteria into skin bite site. Bacteria is carried via lymphatics to small blood vessels to general circulation where they invade epithelial cells (primary target). Spreads to contiguous endothelial cells, smooth muscle cells, and phagocytes. Eventually spreads via the microcirculation and invades all organ systems.
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(MID #296)
Discuss endemic diseases, epidemic diseases, and rashes caused by Rickettsial species. |
(1)ENDEMIC DISEASES: Rocky Mountain Spotted Fever (R. rickettsii), the vector is the tick. Murine typhus (R. typhi), the vector is the flea. (2) EPIDEMIC DISEASES: Rickettsialpox (R. akari) vector is the mite. Epidemic typhus (R. prowazekii), vector is a louse. (3) RASHES: Rickettsial species cause a petechial rash in early diseases that starts on the trunk and spreads outward. Two notable exceptions. R. akari has a characteristic papulo-vesicular rash that looks like chicken pox. R. rickettsii starts on the wrists, ankles, soles, and palms and spreads proximally (centripetal).
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(MID #297)
Rocky Mountain Spotted Fever |
Caused by Rickettsia rickettsii, a fastidious organism (hard to culture and stain). Diagnosis is based on a skin biopsy, PCR, and serologies. Treatment? Doxycycline. Vector: tick. May-September (peak months when ppl are outside w/potential tick exposure). Endemic regions: S. Atlantic and S. Pacific states. After 7-14 d asymptomatic incubation period, sudden onset of fever, headache, malaise, and myalgia. GI disturbances, hepatomegaly, and jaundice can occur in later stages. Rash has 3 stages: (1) erythematous macule (blanches on pressure); (2) macular papular (result of fluid leakage from infected blood vessels); (3) hemorrhage (into center w/frank petechiae). Endothelial invasion leads to angiitis w/local thrombus formation and subsequent end organ damage. Note that R. rickettsii rash starts on the wrists, ankles, soles, and palms and spreads proximally (centripetal).
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(MID #298)
Rickettsialpox |
Caused by Rickettsia akari. Vector: mite. An eschar forms right at the bite site. A papular-vesicular rash w/fever, headache, lymphadenopathy, chilld, myalgia. This is a self-limited disease. Treatment with doxycycline or tetracycline.
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(MID #299)
Epidemic Typhus |
Caused by Rickettsia prowazekii. Vector: louse. Associated w/crowding and poor sanitation. Incubation of approximately one week with the abrupt onset of intense headache, chills, fever, and myalgia. No eschar. Rash starts on the 5th day of illness in the axillary folds and upper trunk, spreads centrifugally, spares face, palms, and soles. Treatment with doxycycline.
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(MID #300)
Ehrlichia |
Small, obligate intracellular GN bacteria that causes a flu-like illness (fever, headache, chills, myalgia, malaise). Symptoms are the same as those of the Rickettsial diseases. Lab results: thrombocytopenia, leukopenia, elevated liver function tests. Pathogenesis: enters via tick bite and spreads via lymphatics to the blood. “Spotless” fever (but 20-30% with human monocytic ehrlichiosis can have a rash). Clustered inclusion-like appearance in the host cell vacuoles. MORULA (Latin for Mulberry). Transmitted by ticks. Multiple species that infect either granulocytes or monocytes.
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(MID #301)
Human Granulocytic Ehrlichiosis (HGE) |
Causative agent: anaplasma phagocytophilum. Vectors: Ixodes ticks. Reservoirs are the white-footed mouse, chipmunks and voles. This is a year-round disease w/one peak incidence in July and another in November. Northeast distribution. Can be severe, with acute respiratory distress syndrome; a septic shock-like picture; rhabdomyolysis (an acute, fulminating, potentially fatal disease of skeletal muscle that entails destruction of muscle, as evidenced by myoglobinemia and myoglobinuria); neurologic sequelae including demyelination polyneuropathy or a brachial plexopathy.
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(MID #302)
Human Monocytic Ehrlichiosis (HME) |
Vector: lone star tick (amblyomma americanum). Reservoir: dog. Seasonal: May-July. Southeastern and Southern Central United States. Treatment with doxycycline or tetracycline.
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(MID #303)
Borrelia |
Causes Lyme disease. Dx: by antibodies. Causative agent is Borrelia burgdorerfi, a treponeme. Vector: Ixodes ticks (nymphs). Reservoirs: the white-footed mouse, white tailed deer, cattle, horses, dogs. Clinical stages of infection: (1) ERYTHEMA MIGRANS. (2) EARLY DISSEMINATED: a) Cardiac – heart block, myocarditis, myopericarditis; b) Musculoskeletal – generalized joint pain, joint effusion – knee is most common; c) Neurological – meningitis, Bell's palsy, peripheral neuropathy, encephalitis (extremely rare); d) Erythema migrans may persist. (3) CHRONIC DISSEMINATED (months to years after bite): a) chronic destructive arthritis of the large joints; b) end stage cardiomyopathy; c) stroke, meningoencephalitis, dementia, peripheral neuropathy which is irreversible; d) acrodermatits chronica atrophicans.
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(MID #304)
What is bacterial menigitis? |
Inflammation of the meninges due to bacterial infection – membranes around the brain and CNS. Not to be confused with encephalitis, which is usually viral and has parenchymal involvement. In severe bacterial meningitis there can be parenchymal pathology and evidence of encephalopathy due to decreased perfusion and local infarcts but the organisms do not invade the brain tissue itself. Bacterial meningitis is usually a complication of bacteremia/sepsis (organisms that seed the meninges, bind to receptors on meningeal cells, and initiate a host inflammatory response). Occasionally due to direct innoculation following trauma or surgery. Usually associated w/specific bacteria that are able to achieve high grade bacteremia and have specificity for meningeal receptors. Intensity of the local immune response to specific organisms is directly correlated w/the amt of pathology and the ultimate outcome. S. pneumoniae elicits significant inflamm response and is often associated w/major neurological sequelae even if the bacteria are totally susceptible to antibiotics.
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(MID #305)
Discuss the epidemiology of NEONATAL bacterial meningitis: (1)Group B Streptococci (Streptococcus agalactiae) (2)E.coli K1 (3)Listeria monocytogenes (4)Coag Neg Staph (premature infants) (5)Candida Albicans (fungus, premature infants) |
Organisms that are part of the mother's vaginal flora & can colonize & cause bacteremia are associated w/neonatal meningitis. (1) Group B streptococci are GP encapsulated organisms. Common commensal flora of women of childbearing age. During or just prior to birth, neonate can aspirate contaminated amniotic fluid resulting in colonization of respiratory tract & stomach. In absence of protective IgG Ab infants (usually following birth complications: prolonged rupture of membranes or associated w/prematurity and/or low birth weight) become bacteremic & develop meningitis. (2) E.coli capsular type K1 (GN rod, common commensal gut flora) has a capsular antigen containing sialic acid in a linkage common to human glycosylated proteins, so many adults lack specific IgG for the K1 capsular antigen. Still, maternal colonization w/K1 E.coli is associated w/much higher incidence of bacteremia & meningitis than colonization with other strains. (3) Listeria monocytogenes is a GP rod that is Catalase (+). Characteristic tumbling motility. Contaminates food fertilized w/manure. Foodborne transmission very common. Associated w/contaminated Mexican-style cheeses & other dairy/poultry products. Very small premature infants are at risk for bacteremia due to normal commensal skin flora – coagulase negative staph. High grade bacteremia can also be associated w/meningitis.
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(MID #306)
Discuss the epidemiology of bacterial menigitis in infants and small children: (1)Streptococci Pneumoniae (2)Neisseria Meningitidis (3)H. Influenzae type B (unvaccinated populations) |
Encapsulated organisms that require specific IgG for efficient phagocytosis. Infants acqurie maternal IgG passively and lose it over the first 6 months-1 year of age. They then acquire their own IgG repertoire over the next few years, leaving a window (6 months to 2 years or longer) when they are at risk for bacteremia and meningitis due to common encapsulated bacteria. Organisms are acquired by direct contact (droplets).
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(MID #307)
Discuss the epidemiology of bacterial meningitis in adults: (1)Neisseria meningitidis (2)Streptococci pneumoniae |
Those at risk lack specific IgG to facilitate phagocytosis or lack splenic function which is important in clearing encapsulated organisms from the blood. Patients w/anatomical defects enabling organisms in the respiratory tract to gain access to the CNS are at higher risk of pneumococcal meningitis. Fractures of the cribriform plate and other basilar skull fractures. In the absence of specific IgG, complement is an alternative means of opsonizing these organisms. Patients w/complement deficiency are at increased risk of meningococcal disease.
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(MID #308)
How do pathogens that cause bacterial meningitis get into the bloodstream? |
Organisms can reach the CNS via hematogenous route or by extension from infection adjacent to the nervous system. Bacteria adhere to nasopharyngeal cells w/specific surfaced structures. [N. meningitidis bind to nasopharyngeal cells and are transported across non-ciliated columnar cells within a vacuole and gain access to the bloodstream.] S. pneumo and H. flu type B attach to specific glycoconjugate receptors on the epithelial surface. Natural Abs of the IgA type in mucosal secretions inhibit adhesion of microorganisms. Ab is due to cross-reactive Ags of nonpathogenic strains and pathogens. Many pathogenic bacteria produce IgA proteases that cleave IgA in the hinge region of the molecule, reach the bloodstream and overcome host defense mechanisms. Their POLYSACCHARIDE CAPSULES are a major virulence factor, allowing them to resist classical complement bactericidal activity and PMN phagocytosis.
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(MID #309)
What factors cause bacterial invasion of the subarachnoid space? |
Cells in the choroid plexus and cerebral capillaries express receptors for bacteria and allow transport of bacteria into the CSF. Outer membrane proteins of bacteria and LPS (GN organisms) and teichoic acid (GP organisms) also are impt in evoking a host inflamm response. Group B streptococci (cause meningitis in infants) recognize specific meningeal receptors and are internalized in glial endothelial cells, where they are protected from the host immune response and many antibiotics.
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(MID #310)
Discuss expression of adhesion molecules causing inflammation in the CNS during bacterial meningitis. |
Once in the subarachnoid space, bacterial proliferation is unopposed: there is NO complement, Ig levels are very low, no resident MF's for surveillance. Bacteria elicit profound inflamm response, causing pathology of meningitis. Response to cell wall fragments, peptidoglycan, & teichoic acid triggers an inflamm cascade. In response, upregulation of endothelial selections (ELAM-1, endothelial leukocyte adhesion molecule), followed by increased expression of integrin ICAM-1 and CD14. WBCs are attracted to the area. PMN migration across endothelium is stimulated. For Gram Negs (like Haemophilus or Neisseria), LPS triggers TNF-alpha and IL-1 expression, activating inflammatory cells and increasing leukocyte binding to the endothelium.
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(MID #311)
What do activated leukocytes in the CNS secrete that cause tissue damage in bacterial meningitis? |
Activated leukocytes in the CNS secrete products which are directly toxic to the surrounding tissue themselves (elastase, reactive oxygen intermediates) or promote pathological changes in the CSF (leukotrienes, vasoactive lipid autocoids). The endothelial barrier is perturbed, causing interstitial edema, impaired resorption of CSF, and loss of the usual autoregulation of CNS blood flow. Amt of inflammation is directly related to clinical presentation. Severity of bacterial meningitis due to H. influenzae type B can be correlated w/levels of TNF in the CSF.
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(MID #312)
In bacterial meningitis, inflammatory response causes derangements in the blood brain barrier. What happens as a result? |
Changes in the usual components of CSF. Intracranial pressure is increased as a result of vasogenic edema, from increased vascular permeability (due to the effects of arachidonic acid metabolites which affect membranes of neuronal cells), and cytotoxic cerebral edema. CNS metabolism of glucose is increased with increased production of lactate. Bacterial meningitis affects blood vessels in the subarachnoid space with resulting vasculitis, vessel narrowing, thrombosis, and ischemia or infarction of the brain. CSF outflow resistance is elevated and inhibits CSF flow from the subarachnoid space to the dural sinuses.
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(MID #313)
How did we reduce the incidence of H. influenzae type B meningitis in children? |
Intro of a vaccine against the type B capsular antigen in 1992. Presence of anti-capsular antibody prevents the high grade bacteremia necessary to enable infection of the meninges. So virtual eradication of H. flu type B meningitis has been achieved based on development of an effective vaccine.
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(MID #314)
Discuss NEISSERIA MENINGITIDIS (Part I) |
N. Meningitidis type B causes sporadic disease and types A and C can cause epidemics. Strains of types D, X, Y, W135, 129E also cause meningitis. Two peaks of disease caused by N. meningitidis: infants <1 yr and the elderly. Organisms attach to epithelial cells of the nasopharynx in patients w/and w/o preexisting Ab. Taken up by receptor-mediated endocytosis and delivered to basolateral side of epithelial cell where they enter the bloodstream. Immune individuals with specific anticapsular Ab [usually from colonization by N. lactamica strains, commensal flora which elicit a protective Ab response] do not become ill. Non-immune individuals develop bacteremia and meningitis.
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(MID #315)
Discuss how an immune adult can transmit NEISSERIA MENINGITIDIS to non-immune individuals in close quarters (Part II) |
An immune adult can be colonized with meningococci without becoming infected since he has Ab. He introduces the organisms into the household exposing non-immune children, in the winter when ventilation is poor and individuals crowd together. Military setting is similar: seasoned soldier w/Ab becomes a carrier and transmits organism to recruits in his barracks. When the carrier state exceeds 30 percent, occasional cases occur in individuals w/o natural immunity. Since Neisseria organisms are present in aerosols formed by coughing and individuals are in close contact w/ one another, colonization will occur.
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(MID #316)
What bacterial factors of N. Meningitidis aid in invasion? |
IgA protease and expression of sialylated glyco-conjugates which mimic neuronal adhesion molecules and do not trigger an appropriate protective antibody response. Particularly true for the type B capsule.
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(MID #317)
What host factors predispose toward meningococcal disease? |
Factors which promote bacterial colonization such as antecedent viral infections, poor living conditions, facilitating spread of organisms to non-immune individuals such as young children, or a military setting. N. meningitides infection is more common in patients who lack higher components of complement (C5-9) which are critically impt in clearing the organism from the blood.
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(MID #318)
Can bacterial meningitis by N. meningitidis be prevented? |
YES! There is a vaccine containing types A, C, Y, and W135. This vaccine is recommended for individuals at high risk of disease: asplenic individuals, those w/deficiencies of terminal components of complement, travelers to endemic areas, military recruits, college freshmen. No effective vaccine against type B, which has an antigenic structure like host neuronal tissue and is not immunogenic.
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(MID #319)
Discuss Streptococcus Pneumoniae and its role in Meningitis. |
Pneumococcal infections (pneumonia, otitis, sinusitis) are very common but only rarely give rise to pneumococcal meningitis. Pneumococcal bacteremia is the antecedent infection. May be coincident w/symptoms associated w/bacterial meningitis. Ab to capsular carbohydrate is critical in the host response. Patients w/impaired splenic function (SS disease) or defects in PMNs are at increased risk for pneumococcal meningitis. Organisms recognize receptors on the meninges and trigger inflammation. Cell wall peptidoglycan fragments are highly immunostimulatory.
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(MID #320)
Is there a vaccine out there for pneumococcal pneumonia? |
Yes! There is a 23-valent pneumococcal vaccine based on carbohydrate antigens of the capsule, that is relatively effective in adults and older children. In infants and young children, there is a realtively new conjugate vaccine in which seven common pneumococcal antigens are linked to protein carriers to elicit a T cell dependent Ab response. Expected to decrease incidence of pneumococcal meningitis in the vaccinated population.
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(MID #321)
How does Meningitis present in neonates? |
Neonates and young infants lack Ab and have defects in PMN chemotaxis and bacterial killing. Do not have a highly developed blood-brain barrier so infections associated with high grade bacteremia can cause meningitis. Clinical presentation of bacterial meningitis in an infant with an open fontanelle and sutures, may be entirely nonspecific. Fever is often but not always present. Lethargy, irritability and eventually vomiting and seizures are common presenting signs.
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(MID #322)
How does Meningitis present in children and adults? |
Fever, headache, lethargy, vomiting, and seizures are frequent findings in children with meningitis. Stiff neck and back pain are also common. Some patients will look flushed but have no neurological signs and only minimal neck stiffness. Others will have altered consciousness, stiff neck, and Kernig and Brudzinski signs indicating meningeal irritation. In adults, severe headache is common as well as altered mental status. Astute clinician should make a diagnosis promptly.
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(MID #323)
What does the lab diagnosis of meningitis look like? |
Peripheral WBC count is elevated. CSF is cloudy due to PMNs. Protein is elevated. Glucose is low. Normal CSF is colorless and clear. Yellowish color is due to breakdown of RBCs or increased protein amt. CSF is grossly turbid if there are >200 WBCs. CSF of normal children and adults contain fewer than 5 cells/mm3. Ratio of glucose in CSF to that in the blood is usually 0.6. CSF glucose levels < or equal to half the serum glucose levels are consistent w/bacterial meningitis due to general disturbance of the BBB.
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(MID #324)
Discuss the sequelae of bacterial meningitis. |
Amt of inflammation, vascular insults and parenchymal damage will all contribute to longterm sequelae. Infants and children w/bacterial meningitis are at significantly increased risk for developmental, hearing, and learning disorders as well as more severe sequelae such as hemiplegias, deafness, and blindness.
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(MID #325)
What is the #1 cause of death due to infectious diseases in the US? |
Pneumonia! Occurs b/c of inflammation in the lung parenchyma caused by bacteria, viruses, or fungi that evade our normal host defenses. Particles in the upper airway can be aspirated or inhaled bypassing normal mechanical protective mechanisms (closure of vocal cords, beating mucociliary cells, alveolar MF's, PMN's, Ab, and complement. The respiratory epithelium produces IL-8 which chemoattracts PMN's.) Microbiologic cause of pneumonia is based on patient's risk factors: age, sick contacts, underlying illnesses, epidemiologic exposures, lifestyle, or place of residence.
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(MID #326)
What are bacterial causes of Community Acquired Pneumonia? |
Streptococcus pneumoniae, non-typeable H. influenzae, S. aureus, Streptococcus pyogenes, N. meningitidis, Moraxella catarrhalis, Klebsiella pneumoniae (and other gram negative rods). Classical picture of pneumonia is acute onset of fever, cough with a focal lobular infiltrate on chest x ray. Other clinical presentations that are more indolent in nature and present with a diffuse interstitial pattern are called atypical. Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella, influenza virus, respiratory syncytial virus, adenovirus, parainfluenza virus, etc. also cause Community Acquired Pneumonia.
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(MID #327)
In patients presenting with what looks like Community Acquired Pneumonia, when would you test for Myobacterium tuberculosis? For Legionella? |
Test for Mycobacterium tuberculosis with acid-fast bacilli staining and culture for patients with cough for >1 month, other common symptoms, or suggestive radiographic changes.
Test for Legionella in selected patients, including all seriously ill patients without an alternative diagnosis, especially if aged >40 years, immunocompromised, or non-responsive to beta-lactam antibiotics, if clinical features are suggestive of this diagnosis, or in outbreak settings. Perform culture and urinary antigen testing for Legionella. Inability to obtain specimens for diagnostic studies should not delay antibiotic treatment of acutely ill patients. |
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(MID #328)
The following epidemiologic conditions are related to what pathogens in patients with selected community-acquired pneumonia? (1)Alcoholism (2)COPD and/or smoking (3)Nursing home residency (4)Poor dental hygiene (5)Epidemic legionnaires' disease (6)Exposure to bats or soil enriched w/bird droppings (7)Exposure to birds (8)Exposure to rabbits |
(1)Alcoholism: S. pneumo and anaerobes; (2) COPD/smoking: S. pneumo, H. flu, Moraxella catarrhalis, and Legionella species; (3) Nursing home residency: S. pneumo, GN bacilli, H. flu, S. aureus, anaerobes, and Chlamydia pneumoniae; (4) Poor dental hygiene: anaerobes; (5) Epidemic legionnaires' disease: Legionella species; (6) Exposure to bats or soil enriched w/bird droppings: Histoplasma capsalatum; (7) Exposure to birds : Chlamydia psittaci; (8) Exposure to rabbits: Francisella tularensis
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(MID #329)
The following epidemiologic conditions are related to what pathogens in patients with selected community-acquired pneumonia? (1)HIV infection (early stage) (2)HIV infection (late stage) (3)Travel to southwestern US (4)Exposure to farm animals or parturient cats (5)Influenza active in the community (6)Suspected large-volume aspiration (7)Structural disease of lung (bronchiectasis, cystic fibrosis, etc.) (8)Injection drug use (9)Airway obstruction |
(1)HIV infection early stage: S. pneumo, H. flu, and Mycobacterium tuberculosis; (2) HIV infection late stage: All of the above plus P. carinii, Cryptococcus, and Histoplasma species; (3) Travel to southwestern US: Coccidioides species; (4) Exposure to farm animals or parturient cats: Coxiella burnetii; (5) Influenza active in the community: influenza, S. pneumoniae, S. aureus, Streptococcus pyogenes, and H. influenzae; (6) Suspected large-volume aspiration: anaerobes; (7) Psuedomonas aeruginosa, Burkholderia cepacia, and S. aureus; (8) Injection drug use: S. aureus, anaerobes, M. tuberculosis, and S. pneumoniae; (9) Airway obstruction: Anaerobes, S. pneumoniae, H. influenzae, and S. aureus.
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(MID #330)
Francisco is a 2 year old boy, previously well, who presented with upper respiratory infection symptoms and fever to primary care physician in July. Respiratory symptoms worsened, chest x ray revealed right-sided pneumonia, WBC count was 24,000 with 80% PMNs and 3% bands. Initially treated with IV therapy without resolution in 4 days. CT scan showed a large right sided effusion. What does this kid have? |
Answer: Streptococcal pneumoniae – a pneumococcal pneumonia. GP diplococci which occurs in pairs or short chains. Virulence is due to capsular polysaccharide. There are 85 capsular types. Capsular polysaccharide is the most impt virulence factor. Protein adhesions that bind epithelial cells in the oropharynx. Secretory IgA protease inhibits function of secretory IgA (which normally binds bacteria to mucin to facilitate clearance from the respiratory tract). Pneumolysin creates pores in and destroys ciliated epithelial cells. H2O2 causes tissue damage. S. pneumo also has teichoic acid, peptidoglycan, and pneumolysin which activate complement.
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(MID #331)
Discuss the epidemiology and clinical presentation of a Streptococcus Pneumoniae infection. |
Common cause of pneumonia especially in pediatric and elderly populations. Incidence is decreasing due to recommendations for universal pneumococcal vaccination for all children starting at 2 months of age. Organism causes many clinical problems including pneumonia, meningitis, otitis media, sinusitis, bacteremia, pericarditis, and arthritis. Diagnosis must be confirmed by blood culture (positive 25% of the time), urine antigen test (may result in false positive tests if patient was recently vaccinated), and sputum culture (difficult to obtain in pediatric patients).
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(MID #332)
Discuss treatment and prevention of infection with Streptococcus Pneumoniae. |
Treatment of streptococcal infections is usually with beta-lactam antibiotics including penicillin, amoxicillin, etc. Incidence of resistance has increased significantly. Cephalosporins, macrolides, quinolones also have activity against pneumococcus. Incidence of disease has decreased a lot with universal use of the pneumococcal vaccine, specifically the conjugated vaccine which has efficacy in kids under age 2 (in contrast to the 23 valent vaccine used in adults). Special populations at risk for pneumococcal disease (asplenics, sickle cell patients, HIV infected patients) should receive pneumococcal vaccination.
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(MID #333)
Myra is a 21-year old medical student living in the dorm studying for exams. She goes to student health complaining of a low grade fever, headache, nonproductive cough, sore throat and general malaise. Her exam reveals mild fine inspiratory rales. Her doctor sends her for an x-ray that reveals bilateral infiltrates. What does she have? |
Classic scenario for Mycoplasma pneumoniae, or walking pneumonia. X-ray appears worse than the aptient looks clinically. Infection with Mycoplasma usually occur in children 5-9 years of age and young adults.
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(MID #334)
Discuss the physiology and structure of Mycoplasma Pneumoniae. |
It is the smallest free-living bacteria. It does not have a cell wall. Cell membrane contains sterols not present in other bacteria. So it is resistant to cell-wall antibiotics such as penicillins, cephalosporins, vancomycin, and others. M. pneumoniae is a strict aerobe and grows only on special enriched media. Grows slowly, most labs don't culture for it. Lab confirmation is usually by serology or PCR-research based. Beside test that suggests diagnosis of mycoplasma include cold agglutinins (IgM antibodies that bind to the I antigen of RBCs). When blood is put on ice, the I antigens appear on RBCs and the Abs cause a snowflaky precipitate to form.
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(MID #335)
Discuss pathogenesis of infections caused by Mycoplasma pneumoniae. |
Mycoplasma has the P1 protein that acts as an attachment factor and facilitates attachment to sialic receptors of the respiratory epithelium and to RBCs. Mycoplasma remains extracellular and interacts with cilia in the respiratory tract causing the cilia and epithelial cells to be destroyed, leading to loss of cells and interference with normal airway clearance leading to contamination of the airway with microbes which cause mechanical irritation and chronic cough. M. pneumoniae also acts as a superantigen stimulating PMNs and macrophages to the site w/subsequent release of cytokines including TNF-alpha, IL-1, and IL-6.
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(MID #336)
Discuss immunity to infections by Mycoplasma pneumoniae. |
Local and systemic immunity to Mycoplasma pneumoniae. IgA appears early and disappears by 4 weeks. IgG appears at 3-4 weeks. The production of cold-agglutinins, a non-specific rxn to the outer membrane of the glycolipids of the M. pneumoniae (IgM antibodies bind to the I antigen on the surface of RBCs when cold) are a useful but nonspecific test. Cold agglutinins are positive in ~65% of symptomatic cases.
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(MID #337)
Discuss the epidemiology and clinical presentation of illness due to Mycoplasma pneumoniae. |
Illness due to M. pneumoniae do NOT follow a seasonal pattern. More common in children, young adults. Cause of 50% of pneumonias for college age students. Infection is spread by droplets so outbreaks occur in close quarters (college, military). Incubation period is 2-3 wks with infections droplets being shed 2-8 days prior to developing symptoms. Produces a mild upper respiratory tract illness (a cold) esp. in young children. Patients develop low grade temperatures (100-102), malaise, headache, dry, non-productive cough that is worse at night and persists for weeks. Lower tract disease may occur in the form of atypical pneumonia since the xray (diffuse interstitial infiltrate) appears worse than the clinical or lab exam of the patient. Occur more often in adolescents suggesting cellular immune response rather than antibody mediated. Complications include otitis media, erythema multiforme (red and white patchy rash often on the hands), hemolytic anemia, myocarditis, pericarditis, neurologic abnormalities.
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(MID #338)
How do you treat infection with Mycoplasma pneumonia? Prevention? |
Treatment with erythromycin or tetracycline (or doxycycline in kids over age 9). Prevention is difficult since the disease is spread by droplets and close contact and organisms are shed for weeks. Isolation is not feasible. No vaccines are available.
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(MID #339)
JM is a 10 week old infant born to a 16 year old mom. Pregnancy history is limited due to lack of prenatal care but the baby is born full term, with no complications, and left the hospital 2 days after birth. Seen by pediatrician at 2 weeks old with eye discharge but was given eye drops. Returned to the ER (2-4 weeks later) with a respiratory rate of 60, cough but no fever. Chest x ray was done and bloods drawn. Child was admitted. What does this baby have? |
Chlamydial pneumonia. Example of Chlamydia trachomatis pneumonia in an infant. Diffuse infiltrates bilaterally with perivascular cuffing. Baby's risk factor was his mom's hx of lack of prenatal care and possibility that she carried chlamydia due to an untreated genital infection. Baby received eyedrops which clear the infection locally without eradicating the organism systemically so the baby went on to develop pneumonia.
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(MID #340)
Discuss the microbiology of Chlamydia in the context of pneumonia. |
Intracellular parasite. Uses host energy ATP. Resembles a GN bacteria even though it is not. Has LPS. Two phase life cycle. Elementary body (EB) is infectious yet metabolically inactive spore-like particle that enters the cell thru various mechanisms including endocytosis via clathrin-coated pits. Converted to the reticulate body (RB) that divides by binary fission in the host cell and is converted back into elementary bodies for extrusion from the cell and infection of new cells.
Chlamydia trachomatis and chlamydophila (pneumoniae and psittaci). The TWAR strain of C. pneumonia is responsible for clinical disease with this organism. |
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(MID #341)
Discuss the pathogenesis of chlamydial pneumonia, and immunity to infection. |
Chlamydial species infect non-ciliated columnar, cuboidal, or transitional epithelial cells found in the respiratory tract. Organisms multiply in alveolar macrophages and perivascular and peribronchiolar infiltrates develop. Clinical manifestations are due to destruction of cells during replication and host inflammatory responses. Immunity is NOT long lasting. Organisms are not readily cultured. Detection relies on ELISA testing or PCR.
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(MID #342)
Discuss Epidemiology, Clinical Syndromes, Prevention and Treatment of C. trachomatis. |
Neonatal pneumonia due to C. trachomatis presents between 1-3 months of life (usually 6 wks). Infants present with a staccato-like cough, rapid respiratory rate, and often DO NOT HAVE FEVER. Wheezing is rarely heard. Diagnostic evaluation reveals hyperinflation and diffuse infiltrates on chest radiograph and a peripheral eosinophilia.
Diagnosis may be made by culture or non-culture tests of the nasopharynx. An IgM antibody test for C. trachomatis w/a titer of greater than 1:32 is strongly suggestive of disease. Kids w/disease consistent w/C. Trachomatis pneumonia should be started on therapy (ERYTHROMYCIN) while waiting for diagnostic test results. Infections in newborns may be prevented by screening and treating pregnant women. |
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(MID #343)
Epidemiology, Clinical Syndromes, Prevention and Treatment of Chlamydophila pneumoniae |
Risk for infection increases w/age. By young adulthood, 50% of the population is seropositive for infection with C. pneumonia. TWAR may cause pneumonia (28% of school-age pneumonias and <10% of adult cases of outpatient pneumonias), bronchitis, and sinusitis (5% of cases) and infrequently pharyngitis (<1%). Asymptomatic carriage of C. pneumoniae has been documented. Disease may result after prolonged incubation of up to 21 days. Respiratory disease due to C. pneumonia has an indolent course beginning with non-specific upper respiratory symptoms (rhinorrhea, sore throat) and progressing to a chronic cough that may persist for weeks despite appropriate antibiotic therapy. Patients are usually afebrile. Chest radiographs show a lobar consolidation, but disease may present as a diffuse interstitial pattern, or with bilateral involvement with pleural effusions and lymphadenopathy. Patients have a normal peripheral WBC count.
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(MID #344)
What illnesses is C. pneumonia associated with? How do you diagnose infection with C. pneumonia? How do you treat it? |
C. pneumonia causes typical pneumonias as well as atherosclerotic disease. Atheromatous plaques have tested positive for chlamydia. Diagnosis of C. pneumoniae is made with serologic testing using microimmunofluorescence tests to detect C. pneumonia specific Ab. IgM Ab develops within 4 wks and IgG by 6 wks. PCR testing of sputum, pharynx, or a pathologic specimen is very specific and provides a more prompt result. Treatment with azithromycin or clarithromycin is preferred to erythromycin or doxycycline due to ease of administration and fewer side effects. Clinical efficacy of >90%. Efficacy rate of levofloxacin (a quinolone) was 98%. Retreatment may be necessary after a 10-14 day course.
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(MID #345)
What disease is caused by Chlamydia psittaci? What is this associated with? |
Associated with sick parrots. Birds may carry/transmit this disease through respiratory droplets. Patient has mild clinical symptoms such as cough, fever, malaise, and the chest radiograph appears worse than expected. Non-specific CNS findings: headache, confusion, cranial nerve palsy, sensorineural hearing loss, meningitis, seizures. Hepatitis, pericarditis may complicate this infection. On physical exam, patients will have fever, pharyngeal erythema, and rales on lung examination. May have Horder's spots on the skin. Pink blanching maculopapular lesions. Chest radiographs may show consolidation, a reticular nodular pattern, and/or hilar lymphadenopathy. Diagnosis of C. psittaci is made by blood culture (within the first 4 days) or sputum culture within the first 2 weeks. (This is hazardous to the respiratory personnel). Serologic testing is perferred. Titers of > 1:64 are diagnostic of infection. Treatment strategies: tetracycline 500 mg 4x/day or doxycycline 100 mg 2x/day for 10-21 days. Erythromycin is an alternative but less efficacious. Most patients respond to therapy within 24 hrs of starting meds.
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(MID #346)
Charlie is a 68-year old retired plumber who recently underwent a renal transplantation. Felt great and was tinkering around his house updating his bathroom fixtures. Came for follow up visit complaining of high fever cough, chills, and his wife said he was acting confused at times. Lab studies reveal WBC 35,000 with left shift, LDH >1000 (lactic dehydrogenase, very high here, indicates some pulmonary process going on). Chest x-ray reveals a multilobar process. What does Charlie have? |
Answer: Infection with Legionella. 2-6% of community-acquired pneumonias. Uncommon among the pediatric population but important consideration in immunocompromised, hospitalized patients, and outbreak situations. There are 39 species and 60 serogroups but the bulk of human disease is caused by L. pneumophila and L. micdadei. Pleomorphic gram negative bacilli. Don't stain with common reagents. Need Dieterle's silver stain. Fastidious organisms, grow in supplemented media (iron salts, L-cysteine). Facultative intracellular ubiquitous aquatic saphrophyte (live inside amoeba). Found contaminating sources of water (air conditioning systems and water tanks).
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(MID #347)
Discuss pathogenesis and immunity w/regard to Legionella infections. |
Legionella is inhaled. Multiples within MF's and monocytes in the alveoli (intracellular). Binds to the complement receptor on alveolar MF's and gets into the cells by endocytosis. Prevents phagolysosome fusion. Organisms survive within cells. Bacilli proliferate in the lungs and produce proteolytic enzymes, phosphatase, lipase, and nuclease which kill the cell when the vacuole is lysed, causing multifocal microabscess formation. Activated/sensitized T cells are needed to kill these organisms by cell mediated immunity. Humoral immunity plays a limited role.
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(MID #348)
Discuss the epidemiology of infections by legionella. |
Disease due to legionella occurs sporadically and epidemically. Incidence peaks late summer to fall. People at greatest risk are those w/impaired cellular immunity and/or compromised pulmonary function (elderly, transplants, neutropenic patients, smokers, alcoholics) and those at risk due to occupational exposure (construction, working w/moist environments and water systems such as cooling towers, hot tubs, showers, etc.)
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(MID #349)
Discuss Legionairre's disease. |
Caused by legionella. Legionnaires' disease is severe pneumonia due to legionella. Incubation period: up to 10 days. Symptoms manifest abruptly with high fevers (105 degrees), rigors, non-productive cough, headache, etc. Pneumonia is multilobar w/microabscesses. Spreads from lobe to lobe. Extrapulmonary manifestations include diarrhea, abdominal pain, nausea, mental confusion or delirium. Lab eval reveals high WBC counts (10-20,000) with a left shift in most cases. Liver and renal function may also be affected. Overall mortality is 15-20% depending on host's immune function. Death is usually due to respiratory or renal failure or shock.
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(MID #350)
What is Pontiac fever? |
Due to legionella pneumophila. Self-limited febrile illness like the flu (fever, chills, myalgia, headaches, etc.) Symptoms last 2-5 days and resolve spontaneously.
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(MID #351)
How do you diagnose infection with legionella? |
Direct fluorescent antibody (DFA) test in which flurorescein-labeled monoclonal or polyclonal Abs are directed against Legionella species. Legionella can be cultured on special media, buffered charcoal-yeast extract agar. Legionellosis is usually diagnosed by serology with a fourfold or greater increase in Ab titer (1:128 or greater) considered positive. Antibody titers are not usually seen until 3 weeks into the illness. Titers may persist for >1 year.
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(MID #352)
How do you prevent and/or treat infection with legionella? |
Macrolide antibiotic (azithromycin, erythromycin) or levofloxacin (a quinolone). Beta-lactam antibiotics are usually NOT effective due to production of beta-lactamases by the bacteria. Hyperchlorination and superheating have been used to eliminate legionella bacilli from the water supplies. Low levels of organisms can persist and usually don't cause disease. If complete elimination is necessary, continuous copper-silver ionization must be used.
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(MID #353)
Jerry is a 7 month old baby with a runny nose, sneezing and slightly irritable. He is diagosed with an upper respiratory tract infection. He returns two weeks later because he is turning blue with coughing spells. Spells are worse at night. He seems to have spasms and then “whoops” for air. Exam reveals mildly dehydrated, not distressed, clear lung exam. WBC reveals leukocytosis with lymphocytosis. What does Jerry have? |
Jerry has “Whooping Cough” an infection with Bordetella pertussis. Acute respiratory infection marked by episodic spasmodic coughing in the paroxysmal phase. Causes significant clinical disease as bronchopneumonia in young children. Bordetella organisms are small, aerobic, fastidious, gram negative coccobacilli. Requires special media (Bordet-Gengou agar) to grow. Culture can be used for diagnosis. Serologic tests can be used following acute and convalescent titers.
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(MID #354)
Discuss the pathogenesis of Bordetella pertussis infections. |
Pertussis is spread by respiratory droplets. Organism colonizes and rapidly multiplies in the mucus membrane of the respiratory tract. No bacteremia. Disease is caused by TOXINS that cause local tissue damage. B. Pertussis attaches to ciliated epithelial cells in the respiratory tract. Facilitated by action of pertussis toxin and filamentous hemagglutinin. Pertussis toxin has an A-B subunit. The A unit has the toxic subunit (S1) and the B unit has 5 binding subunits (S2-S5) which help with binding. S2 binds to respiratory epithelium. S3 binds phagocytes. Filamentous hemagglutinin binds respiratory epithelial cells and PMNs and facilitates uptake into those cells. Other adhesions (pili and pertactin) help bind the organism to cells.
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(MID #355)
Discuss toxin production and disease manifestations by B. pertussis. |
PERTUSSIS TOXIN: The S1 portion of pertussis toxin has ADP-ribosylating activity for the surface G protein (function is to regulate adenylyl cyclase activity). Causes cAMP levels to be unregulated resulting in increased respiratory secretions and mucus production characteristic of the paroxysmal state of pertussis. ADENYLATE CYCLASE/HEMOLYSIN TOXIN is activated by intracellular calmodulin and catalyzes conversion of ATP to cAMP. Adenylate cyclase toxin inhibits leukocyte chemotaxis, phagocytosis, and killing. HEAT-LABILE TOXIN causes local tissue destruction. TRACHEAL CYTOTOXIN destroys ciliated epithelial cells by inhibition of cilia movement and by causing extrusion of the cells. Stimulates the release of IL-1 which causes fever and the release of nitric oxide from the respiratory cells which in turn kills the epithelial cells. LIPID A and LIPID X are lipopolysaccharides produced by pertussis. Activate the alternative complement pathway and stimulate cytokine release.
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(MID #356)
Discuss the epidemiology of pertussis related illness. |
Has declined since intro of a vaccine in 1949. Still endemic around the world. Primarily affects kids under age 1. Increasing number of cases in older children and adults due to waning immunity. Unvaccinated persons and young children are at highest risk for the disease. Aerosolized droplets infect the host. After a 7-10 day incubation period, the patient develops symptomatic disease in 3 stages. 1st Stage: Catarrhal stage, resembles common cold with rhinorrhea, sneezing, malaise, anorexia, and low-grade fever. 2nd Stage: Paroxysmal Stage. Occurs 1-2 wks after symptoms have begun. Patient coughs and “whoops”. Vomiting after these common spasms is common. Lymphocytosis is noted. Symptoms are due to intense inflammatory response in the airway causing local obstruction and airway plugging. 3rd Stage: Convalescent Stage. After 2-4 wks, cough is subsiding. Other complications occur: pneumonia (due to other organisms that colonize the airway), seizures, and encephalopathy.
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(MID #357)
How do we prevent and treat Whooping Cough? |
B. pertussis is susceptible to erythromycin. Antibiotics do not alter the course of infection but may decrease communicability. Treatment is supportive. Whole-cell inactivated vaccines and multivalent acellular vaccines combining diphtheria, pertussis, and tetanus (DPT) are commonly administered to most US children and are 80-85% effective. Acellular vaccines are preferred due to lower incidence of side effects such as pain, erythema at the site, and fever. Kids 11-12 yrs old get a Tdap booster (Tetanus, diphtheria, and acellular pertussis vaccine). Adolescents 13-18 yrs old who missed their Td/Tdap booster dose should receive a single dose of Tdap if they have completed the recommended childhood DTP/DTap vaccination series.
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(MID #358)
What antibiotics inhibit synthesis of bacterial cell walls? |
(1)Penicillins
(2)Cephalosporins (3)Carbapenams (4)Monobactams (Aztreonam) (5)Vancomycin |
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(MID #359)
What agents affect the function of 30S and 50S ribosomal subunits to cause a reversible inhibition of protein synthesis? |
(1)Chloramphenicol
(2)Tetracyclines (3)Glycylcyclines (tigecycline) (4)Macrolides (5)Clindamycin (6)Streptogramins (quinupristin/dalfopristin) (7)Oxazolidinones (linezolid): binds to the 23S ribosomal subunit of the 50S ribosome. |
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(MID #360)
Which agents bind to the 30S ribosomal subunit and alter protein synthesis, eventually leading to cell death? |
(1)Aminoglycosides
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(MID #361)
Which agents affect bacterial nucleic acid metabolism? |
(1)Rifamycins (rifampin): inhibit RNA polymerase
(2)Quinolones: inhibit topoisomerase IV and DNA gyrase |
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(MID #362)
Which agents block essential enzymes of folate metabolism? |
(1)Trimethoprim
(2)Sulfonamides |
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(MID #363)
Miscellaneous antimicrobial agents? |
(1)Daptomycin
(2)Metronidazole (3)Polymyxins |
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(MID #364)
Discuss the Beta-lactams |
Penicillins, cephalosporins, carbapenams, and monobactam. Inhibit synthesis of the cell wall by blocking the action of transpeptidases (penicillin binding proteins).
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(MID #365)
Discuss Vancomycin |
Inhibits the late stages of peptidoglycan synthesis. Binds to D-Ala-D-Ala terminals of the pentapeptide-ending precursors localized at the outer surface of the cytoplasmic membrane.
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(MID #366)
Explain how the protein synthesis inhibitors work! |
(1)Aminoglycosides: Block the initiation of translation and cause misreading of mRNA. Works on the 30S subunit.
(2)Tetracyclines: Block the attachment of tRNA to the ribosome. Works on the 30S subunit. (3)Streptogramins: Each interferes with a distinct step of protein synthesis. 50 S subunit. (4)Macrolides: Prevents the continuation of protein synthesis. 50S subunit. (5)Chloramphenicol: Prevents peptide bonds from being formed. 50S subunit. (6)Lincosamides: Prevents the continuation of protein synthesis. 50S subunit. (7)Oxazolidinones: Thought to interfere with the initiation of protein synthesis. 50S subunit. |
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(MID #367)
Discuss the Rifamycins |
Inhibit RNA polymerase.
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(MID #368)
Discuss the Quinolones |
Inhibit the activity of topoisomerases, which are enzymes responsible for the supercoiling of the DNA (DNA gyrase) and relaxation of the supercoiled DNA (topoisomerase IV).
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(MID #369)
Discuss the actions of trimethoprim and the sulfonamides. |
Inhibit folate metabolism at two successive points in the same pathway. Synergistic.
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(MID #370)
What is Daptomycin's mechanism of action? |
Calcium-dependent binding and insertion of daptomycin's lipophilic tail into gram-positive bacterial cytoplasmic membrane. Oligomerization and channel formation occurs. Ion leakage and collapse of organism lead to cell death.
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(MID #371)
What is Metronidazole's mechanism of action? |
Metronidazole enters an aerobic bacterium where, via the electron transport protein ferrodoxin, it is reduced. The drug then binds to DNA and DNA breakage/fragmentation occurs.
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(MID #372)
Antibiotics can be used in 3 distinct ways: empiric therapy, definitive therapy, and prophylactic or preventative therapy. Discuss these. |
(1)Empiric therapy must cover all likely pathogens as the infecting organism(s) has not yet been identified. This is referred to as “broad spectrum” therapy. (2) Once the infecting organism(s) has been identified, therapy becomes definitive, meaning an antimicrobial is chosen that specifically targets the microorganism identified and has the least potential to cause harm to the patient. This results in the use of an antimicrobial with a narrower, more targeted spectrum of activity. (3) Finally, therapy may be prophylactic or preventative, attempting to prevent an infection or its recurrence. **Remember: Antibiotics can cause serious toxicity and injudicious use promotes selection of resistant bacteria.
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(MID #373)
Before prescribing an antibiotic one must confirm the presence of an infection. How do we do this? |
Careful history and physical exam noting all signs and symptoms suggestive of an infection, including relevant lab data. Infections may be ID's by: fever, elevated WBC counts, swelling, redness (erythema), purulent drainage from a visible site, the presence of WBC in normally sterile fluids such as spinal fluid, urine.
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(MID #374)
Discuss ID of the pathogen and the MIC |
Sample infected body materials (urine, sputum, blood, wound drainage), before initiation of antimicrobial therapy. Gram stain may be helpful for quick detection of potential organisms causing infection and aid in choosing appropriate therapy. Once the organism is ID'd the susceptibility to various organisms is reported as susceptible (S), intermediate (I), or resistant ®. Determined by interpretation of the minimum inhibitory concentration (MIC), which is defined as the lowest concentration of drug that prevents visible bacterial growth after 24 hours of incubation in a specified growth medium. MIC values are organism and antimicrobial specific.
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(MID #375)
Distinguish between resistant, intermediate, and susceptible isolates with regard to MIC and particular antimicrobials. |
Interpretation of the MIC requires knowledge of drug pharmacokinetics, drug's activity vs the organism, and site of infection. (S) Susceptible implies that the infection due to the strain may be appropriately treated with the dosage of antimicrobial agent recommended for that type of infection and infecting species (levels of antimicrobial will be equal to or above the MIC.) (I) Intermediate implies drug may be used in body sites where drugs are physiologically concentrated or when a high dosage of drug can be used. Isolates w/MICs that approach usually attainable blood and tissue levels, for which response rates might be lower than for susceptible isolates. (R) Resistant implies that strains are not inhibited by the usually achievable systemic concentrations of the agent with normal dosing schedules and/or fall in range in which specific microbial resistance mechanisms are likely and clinical efficacy has not been reliable. Levels of antimicrobials most likely will NOT be above MIC.
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(MID #376)
Describe DISK DIFFUSION |
Classical method of testing for antimicrobial susceptibility. Antimicrobial agent diffuses from a cellulose filter paper disk (Kirby-Bauer disks) onto a solid medium surface over which bacteria have been streaked. After 24 hrs incubation, the zone of inhibition of bacterial growth around the disk is measured. Provides a qualitative result (S, I, R) as no specific MIC number is reported. Based on size of the zone, organisms can be considered susceptible, intermediate, or resistant.
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(MID #377)
Discuss BROTH DILUTION |
Broth dilution uses various concentrations of antimicrobial agents in test tubes containing liquid medium to which a standard inoculum of the test organism is added. Test tubes are incubated for 24 hrs and the lowest concentration of antimicrobial at which no visible growth is noted is referred to as the MIC.
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(MID #378)
Discuss the E-Test |
E-test is a method by which a gradient of increasing concentrations of test antimicrobial is incorporated into a single plastic coated strip. E-strip is placed on solid agar onto which the test organism has been streaked. After overnight incubation, the MIC is determined by visually identifying the intersection of the lowest point of the elliptical zone of growth inhibition and the gradient strip.
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(MID #379)
Discuss pharmacokinetic factors which impact the success of an antimicrobial agent against an infectious organism. |
IV forms of drug are 100% bioavailable. Be aware of drug interactions with other compounds or foods that may bind the drug and prevent it from being absorbed or a disease state that may adversely affect the site of absorption. Volume of distribution is impacted by lipid solubility, blood flow to tissues, pH and protein binding. Drugs with small Vd have limited distribution, whereas drugs with large distribution volumes are extensively distributed throughout the body. Drug metabolism occurs in the liver, small intestine, other organs. Phase I rxn cause inactivation of the substrate w/a resulting cmpd that is more polar than the parent cmpd facilitating elimination from the body. Phase I rxns are under control of the Cytochrome P-450 system. Phase II rxns involve conjugation of parent cmpd with larger molecules, increasing polarity, facilitating excretion. Elimination of drug occurs by renal and nonrenal clearance. Renal clearance describes rate at which body eliminates a substance via the kidneys. Nonrenal clearance primarily denotes hepatic clearance, but may include biliary tree or intestine. Clearance affects half life (time req'd for blood concentration of the drug to decrease by half). Steady-state is achieved once patient has been taking the drug for 4-5 half lives.
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(MID #380)
Discuss pharmacodynamic properties of antimicrobials: bactericidal vs. bacteristatic |
Desirable effects can be classified as STATIC (inhibitory) or CIDAL (lethal). Antimicrobial may inhibit growth or replication or cause bacterial cell death. Interference in development of bacterial cell wall or membrane (beta-lactams, vancomycin) results in cell lysis and death. Antimicrobials that inhibit nucleic acid synthesis (quinolones) or protein synthesis (aminoglycosides) also lead ultimately to cell death. Inhibition of folic acid synthesis (sulfonamides) may only cause inhibition of bacterial growth. Antimicrobial concentration at the site of the infection also affects whether a drug is bacteristatic or bactericidal – may be static at low concentrations but cidal at higher concentrations. If the host is compromised or infection is severe and/or invasive, cidal therapy is preferred.
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(MID #381)
Discuss the difference between concentration-dependent and concentration-independent (time-dependent) killing agents. |
(1)Quinolones and aminoglycosides are concentration dependent killers. They eliminate bacteria when their concentrations are well above the MIC of the organism. When the ratio of the concentration at the site of infection to the MIC is increased further, greater killing occurs. The ratio of Cmax divided by MIC of the organism predicts outcome for concentration dependent killing agents. (peak/MIC ratio = IMPORTANT!) (2) Concentration independent (time-dependent) killing agents (penicillins, cephalosporins) kill bacteria only when the concentration at the site of the bacteria is higher than the MIC of the organism. Once the concentration at the bacterial site is more than 4x higher than the MIC, little additional killing occurs. The time during which serum drug concentration is greater than the MCI is the pharmacodynamic parameter that predicts efficacy for these agents (time>MIC = IMPORTANT!)
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(MID #382)
What is the POST ANTIBIOTIC EFFECT? |
PAE is the delayed regrowth of bacteria following exposure to an antimicrobial (continued suppression of normal growth in the absence of antibiotic levels above the MIC of the organism). Presence and duration of MIC varies according to drug-bug combo. Most beta-lactam agents (penicillins, cephalosporins) exhibit a PAE of 1-2 hrs against GP oragnisms. Against GN organisms, beta-lactams exhibit a negligible PAE while aminoglycosides and quinolone have PAE > 2 hrs.
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(MID #383)
Discuss TOXIC effects of antimicrobials. |
Important to avoid toxic drugs whenever possible. Prolonged use of various agents may predispose patients to hematologic toxicities. The nephrotoxicity of aminoglycosides and vancomycin may worsen preexisting renal dysfunction or augment the risk of other non-antimicrobial nephrotoxic drugs.
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(MID #384)
Discuss ALLERGIC responses to antimicrobials. |
Previous history of allergic rxn to a drug being considered or one that is immunochemically similar is the most reliable risk factor for development of a subsequent allergic rxn. Patients with a history of penicillin allergy – all structurally related penicillin compounds should be avoided, and possibility of rxn should be considered with use of other beta-lactam antibiotics. Need to determine whether reaction was intolerance, toxicity, or true allergy. For instance, GI intolerance from erythromycin is common but the drug can still be used. Avoid the use of a drug or related compound if the patient has experienced a true allergic reaction (anaphylaxis, bronchospasm, etc.) Patients with delayed reactions to penicillin (skin rash) can generally receive cephalosporins (5-10% cross reactivity). Patients with type I hypersensitivity rxns to penicillins (anaphylaxis) should not receive cephalosporins. Consider alternatives: aztreonam, quinolones, sulfa drugs, vancomycin).
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(MID #385)
Discuss the effects of AGE on bacterial infection. |
With bacterial meningitis, neonates are at greater risk from Listeria and group B Streptococcus, adults are at greater risk from Streptococcus pneumoniae and Neisseria meningitides, and elderly patients are at greater risk of meningitis caused by Streptococcus pneumoniae and Listeria. Also, be aware that in premature and newborn children and the elderly, renal function is diminished and half-lives of drugs excreted by the kidneys may be increased (patients requires less drug). Hepatic function is diminished in neonates.
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(MID #386)
Discuss the effects of PREGNANCY on bacterial infection. |
During pregnancy, fetus is at risk for drug teratogenicity and pharmacokinetic disposition of drugs may be altered. ALL antimicrobials cross the placenta in varying degrees so one should avoid agents known to be teratogenic. Penicillins, cephalosporins, and erythromycin appear to be safe in pregnancy. Avoid ticarcillin, metronidazole (teratogenic in rodents), and tetracyclines (bind to developing bones and teeth, causing discoloration). Not sure about quinolones, rifampin, or trimethoprim. Penicillins, cephalosporins, and aminoglycosides are cleared more rapidly during pregnancy (increases in intravascular volume, glomerular filtration rate and hepatic and metabolic activities) and increased dosages may be necessary to achieve therapeutic drug levels during late pregnancy.
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(MID #387)
Discuss genetic or metabolic abnormalities and antimicrobial therapy. |
Patients with peripheral vascular disease have impaired absorption of intramuscularly administered drugs. Patients w/severe glucose-6-phosphate dehydrogenase (G6PD) deficiency may develop hemolysis when administered sulfonamides, nitrofurantoin, dapsone, antimalarials, and chloramphenicol. Mild deficiencies are found in African American. Most severe forms of the disease are found in persons if Eastern Mediterranean origin.
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(MID #388)
Discuss renal/hepatic function and their effects on antimicrobial therapy. |
Patients with diminished renal or hepatic function, or both, will accumulate certain drugs metabolized and/or excreted by these routes. Patients are at increased risk of drug toxicity unless dosage is adjusted. Important to remember that renal excretion is the most important route of elimination for the majority of antimicrobials. Presence of severe liver disease may require dosage adjustment for agents relaying predominantly on hepatic metabolism for elimination (e.g., clindamycin, macrolides, metronidazole, and rifampin).
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(MID #389)
Of all the host factors to be considered in the choice of an antimicrobial agent, none is more important than the site of infection!! |
Discuss. Site of infection defines most likely organisms and is helpful for choosing an agent for empiric therapy. The majority of UTIs are caused by GN bacilli, like E.coli. Bacteremia from an intravascular catheter is often caused by Staphylococcus. Site of infection also determines dose and route by which drug should be administered. Adequate concentration of drug must be delivered to the infection site. Minimal drug concentration at the infected site should be approximately equal to the MIC for the infecting organism, and it is recommended to achieve multiples of this concentration if possible, especially with concentration-dependent killing agents. Access of antimicrobials to sites of infection depends on multiple factors. If infection is in the CSF, the drug must cross the BBB and many antimicrobials do this poorly. Treatment of meningitis, endocarditis, and osteomyelitis require higher doses and more prolonged therapy w/agents that have adequate penetration to the site of infection. IV administration of antimicrobials is usually recommended in seriously ill patients in whom predictable concentrations of drug must be achieved (bacteremia, meningitis, endocarditis).
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(MID #390)
Discuss concomitant drug therapy and antimicrobial treatment. |
(1)Decreased absorption of quinolones is caused by concomitant administration with multivalent cations (calcium, magnesium, aluminum containing antacids) and (2) rifampin decreases the anticoagulant effect of warfarin secondary to increased hepatic metabolism caused by rifampin. SYNERGY results when addition of drug A to drug B results in a total antimicrobial activity greater than the expected sum of the two agents (penicillin + aminoglycoside against Enterococci). ANTAGONISM occurs when addition of drug A to drug B results in combined activity less than the sum of drug A + drug B. INDIFFERENCE means the addition of drug A to drug B results in activity equal to the anticipated sum of drug A + drug B. Also, toxicity can increase when drugs are given together, with additive or superadditive toxicity. Vancomycin used alone has minimal renal toxicity, but when given with an aminoglycoside, the renal toxicity risk is increased.
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(MID #391)
What is the affect of UNDERLYING DISEASE STATES on antimicrobial therapy? |
Immunosuppressive diseases (malignancies, organ transplant patients, HIV + patients) predispose patients to infections. Type of organisms causing the infections may differ from a normal host. Bacterial meningitis in an otherwise healthy adult is commonly caused by Streptococcus pneumoniae or Neisseria meningitides. May be caused by Listeria monocytogenes in a patient with lymphoma. Also, when renal and hepatic function are compromised it affects elimination of antimicrobials from the body and there is increased risk of toxicity.
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(MID #392)
Discuss monitoring of patient response to antimicrobials. |
WBC count and temperature should normalize. Physical complains should diminish. Radiologic improvement may lag behind clinical improvement. Determination of serum levels of antimicrobials may be useful in assuring outcome, preventing toxicity, or both. Only a few antimicrobials require serum concentration monitoring, and then only in selected situations (i.e. Aminoglycosides). Important to monitor patient tolerability of the antimicrobial regimen. Appropriate lab tests (e.g., serum creatinine, liver enzymes) should be monitored to minimize or avoid antimicrobial drug toxicity. Antibiotic route of administration should be evaluated daily. Streamlining from intravenous to oral antimicrobials should be attempted as signs of infection improve for patients with functioning GI tracts. General exceptions are bloodstream and CNS infections, in which case meds should remain IV. If patients do not respond to an appropriate treatment in 2-3 days, they should be reevaluated to ensure infection is the correct diagnosis, therapeutic drug concentrations are being achieved, the patient is not immunosuppressed, the patient does not have an isolated infection (abscess, foreign body), or resistance has not developed.
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(MID #393)
What are the beta-lactam antibiotics? |
Cephalosporins, Penicillins, Carbapenams, and Monobactams. These beta-lactam drugs target the bacterial cell wall. (Mammalian cells lack cell walls). They are CIDAL to actively growing organisms, meaning that they KILL bacteria. There is a structural resemblance between the backbone of penicillin and the D-ala-D-ala portion of the pentapeptide chain of the peptidoglycan that is cross-linked to make bacterial cell walls. Penicillin-binding-proteins (PBPs) are the enzymes needed for peptidoglycan synthesis and fall into 2 groups: (1) Carboxy-peptidases, which cleave the terminal D-ala from the pentapeptide releasing ATP and exposing the amino acid to be crosslinked and (2) Transpeptidases which perform the cross-linking reaction. Beta-lactam antibiotics are only cidal to actively growing organisms. The affinity of a specific beta-lactam drug for these PBPs will determine its potency. Staphylococcus aureus is a common pathogen that is often susceptible to beta-lactam antibiotics: penicillin and cephalosporins. By mutating PBP2, the organisms become resistant to this entire class of antibiotics, yielding methicillin resistant Staph aureus (MRSA).
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(MID #394)
What properties of an antibiotic determine its activity against specific bacteria? |
(1)Affinity of the drug for the target;
(2) Permeability of the drug (how well it can get to its target); (3) Stability to bacterial enzymes that inactivate or destroy the drug. |
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(MID #395)
How does the beta-lactam drug get to its target, the penicillin binding proteins in the bacteria? Permeability properties of a drug are critical. Also depends on whether bug is extracellular (in the bloodstream) or intracellular and sequestered within a MF. The bacteria could be encased in a mucus plug in the airways or within an intra-abdominal mass. Discuss permeability issues in Gram positive vs. Gram negative bacteria. |
GN organisms have an outer cell wall, a lipoprotein barrier studded w/protein channels (porins). Charged antibiotics like beta-lactams must get through the porin proteins to reach their targets, the PBPs which are on the inside of the outer lipoprotein cell wall. A potential space called the periplasmic space occupies the region between the outer cell wall and the peptidoglycan. Bacteria regulate what goes through these porins: electrolytes, amino acids, and sugars. Since the porins are large, they don't pose a major barrier to beta-lactam antibiotics. GN respiratory pathogens such as Hemophilus and Neisseria species have large porins and are relatively susceptible to beta-lactam drugs.
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(MID #396)
Are beta-lactam antibiotics effective against opportunist Gram negative bacteria, such as Pseudomonas, Enterobacter, and others? |
These bugs can synthesize whatever they need from small sized components. Their porins are highly regulated, small, and pose a MAJOR BARRIER for entry of beta-lactams to the periplasmic space and access to the PBPs. These organisms have EFFLUX PUMPS which can be activated to pump the antibiotics back out the porins, even if they do get to the site of peptidoglycan synthesis. The beta-lactam antibiotics with the best permeability properties for these Gram negatives are zwitterions, compact structures that are efficiently taken up by these porins.
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(MID #397)
Are beta-lactam antibiotics effective against Gram positive bacteria? |
Gram positive bacteria lack an outer cell wall, but instead have multiple layers of peptidoglycan. This peptidoglycan forms a loose mesh that doesn't pose a significant permeability barrier to the hydrophilic beta-lactam compounds. Beta-lactams can have relatively bulky side chains and still gain access to their target PBPs in these gram positive organisms.
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(MID #398)
How do bacteria respond to β-lactam antibiotics? |
Bacteria evolved mechanisms to deal with the presence of these antimicrobials by the production of β-lactamases. These enzymes cleave the β-lactam ring and destroy the ability of the β-lactam drug to bind to the target PBP. Many organisms, particularly GN opportunists, have inducible beta-lactamase expression that is chromosomally mediated and turns on and off depending on presence of an inducer. Mutants can be selected that are stably derepressed. Chromosomal enzymes may prefer the 5-membered penicillin nucleus or the 6-membered cephalosporin nucleus as a substrate. There are also plasmid-encoded β-lactamases that are constitutively expressed and can be transferred from on organism to another. There are >30 variants of these TEM enzymes (that destroy β-lactam antibiotics). Plasmid-mediated enzymes have expanded their spectrum of activity to include not just simple penicillins but also 6-membered cephalosporin rings as well. Called “extended-spectrum β-lactamases) since they are often plasmid mediated, they are transferable in places that many bacteria co-mingle such as the gut flora.
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(MID #399)
Where are β-lactamases located in GN and GP bacteria? |
In GN bacteria, beta-lactamases are strategically placed in the potential “periplasmic space” where cmpds entering the cell via porins would be immediately detected. Economy of β-lactamase production and efficient use of the enzymes. Competition between affinity of the incoming antibiotic and its target PBPs and the affinity of the β-lactamase for the drug. If two drugs were entering simultaneously, one w/substantial affinity for β-lactamase and one with more affinity for PBP, it would be possible to competitively inhibit the β-lactamase and let the penicillin kill the bacteria.
GP bacteria lack this outer cell wall so β-lactamses are synthesized and secreted into a “cloud” surrounding the organism. Antibiotics that approach the organism must be stable to these enzymes once they reach the vicinity of the bacteria. However, since there are no porin protein channels to squeeze through, bulky side chains that sterically inhibit β-lactamase activity can be added to penicillins targeting GP organisms such as Staphylococci that produce β-lactamases. |
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(MID #400)
Discuss mechanisms by which antimicrobials can be designed to avoid destruction by β-lactamases. |
Amoxicillin is an oral penicillin that kills GP and some GN respiratory pathogens. Most often used to treat respiratory tract infections and otitis media. Susceptible to β-lactamase destruction. By adding clavulanic acid, a specific β-lactamase inhibitor, to the amoxicillin formulation, the combination AUGMENTIN (amoxicillin + clavulanate) is active against β-lactamase producing organisms in the respiratory tract, such as Hemophilus or Neisseria. Also active against staphylococci that are producing β-lactamases.
To target GP organisms (such as Staph) the anti-staphylococcal penicillins were developed that contain a large side chain making the β-lactam ring inaccessible to the bacterial enzymes. These bulky penicillins don't get through porins so they are limited to Gram positives. |
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(MID #401)
Discuss Kirby-Bauer Disc Diffusion and E Strips |
Filter paper disc is soaked in standardized concentration of antibiotic and placed on a plate that has been inoculated with a known concentration of bacteria. Following incubation at 37 degrees C overnight, the size of zones surrounding the discs are measured and compared to standards for each drug that reflex that amt of drug expected to be achieved in a patient. If the zone is large enough, the bacteria is considered susceptible. If bacteria grow across the disc, they are resistant. E strips are based on the same principle: filter paper soaked in graded amts of the drug enabling the technician to directly read the concentration of an antibiotic that kills the organism.
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(MID #402)
Discuss Minimum Inhibitory Concentration and Minimum Bactericidal Concentration |
MIC: Bacteria are inoculated into 96 well microtiter plates with decreasing concentrations of antibiotics. After overnight incubation turbidity is read spectophotometrically and the well without turbidity is considered the MIC.
MBC: In liquid culture a small number of organisms does not result in turbidity. But if the liquid were placed on solid media, colonies could arise if there were still a few bacteria present. The MBC is measured by plating out the 'clear' liquid media and establishing the concentration where there is >99.9% killing. |
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(MID #403)
Discuss Penicillin G |
Prototype: β-lactam ring + a thiazolidine ring + R groups (which are side chains that influence pharmacologic properties). Not β-lactamase stable but is highly active against streptococci, spirochetes (which cause syphilis and Lyme disease) and meningococci. Penicillin G is not acid stable so it is given parenterally: either intravenously or in a repository form (procaine pen G or benzthine pen G) which is given intramuscularly.
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(MID #404)
Discuss Ampicillin and Amoxacillin |
Addition of a charged NH3 group improves the penetration of the penicillin nucleus thru Gram negative porins in organisms like E.coli while retaining excellent activity against Streptococci. OH group in amoxicillin provides stability to stomach acid. Neither ampicillin nor amoxicillin is β-lactamase stable so they are often given in combination with a β-lactamase inhibitor.
Ampicillin + Sulbactam = Unasyn: used parenterally for a wide variety of infections including those caused by anaerobic bacteria, GN and GN organisms. Amoxicillin + Clavulanic acid = AUGMENTIN: Oral drug commonly used for respiratory infections. Covers S. aureus since the clavulanate inhibits the Staphylococcal β-lactamase, as well as β-lactamase producing Hemophiolus and Moraxellae. |
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(MID #405)
Discuss the Anti-Staphylococcal Penicillins (Oxacillin, Methicillin, Nafcillin) |
The anti-staphylococcal penicillins (also referred to as semisynthetic) were developed in the 1950s to deal with the problem of Staphylococcal infections due to penicillin resistant organisms. S. aureus strains produced β-lactamases with primarily penicillinase activity. Adding a large bulky side chain (methoxy or isoxaoyl groups) protected the β-lactam bond and did not interfere with penetration to the target PBP's since these Gram positive bacteria have no outer cell walls. Cloxacillin and di-cloxacillin are oral forms of these drugs used for staph infections.
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(MID #406)
Discuss the Anti-Pseudomonas Penicillins (Piperacillin) |
To kill the opportunists, the Gram negative bacteria with tightly regulated porin channels and multiple efflux systems, broad spectrum penicillins were developed with charged R side chains to improve permeability thru the porins and with structural properties that increase affinity for the PBP3 target. Piperacillin has a piperazine ring, a compact charged group that significantly enhances the activity of the drug against P. aeruginosa, a common GN opportunist. Piperacillin is formulated with a β-lactamase inhibitor (TAZOBACTAM) = Zosyn, which provides protection against plasmid mediated β-lactamases, particularly those of the TEM type. Taobactam does not protect against the derepressed chromosomal β-lactamase of P. aeruginosa (ampC) which has predominantly cephalosporinase activity. The combination of piperacillin + tazobactam provides broad spectrum activity against Gram positive bacteria (streptococci and staphylococci) as well as many enteric Gram negatives (E.coli, Klebsiella, Proteus species) and opportunistic pathogens (P. aeruginosa).
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(MID #407)
Mechanisms of resistance to penicillins: MUTATIONS in Penicillin Binding Proteins |
Bacteria spontaneously undergo mutation at a frequency of 10^6-7. In the presence of an antibiotic, mutations that enhance survival are selected and organisms with those mutations predominate. Streptococcus pneumoniae, a very common GP respiratory pathogen, can accumulate mutations in the PBPs and become relatively or absolutely resistant to penicillin. When these organisms die and lyse, their DNA is take up by other streptococci (naturally transformable) and in the presence of antibiotic selective pressure, the transformed penicillin-resistant organisms are maintained in the population. A DNA cassette which encodes a mutant PBP2 in S. aureus is also a common clinical problem causing methicillin resistant S. aureus (MRSA).
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(MID #408)
Mechanisms of resistance to penicillins: β-lactamase production |
Both GP and GN organisms can produce β-lactamases that cause clinically significant antibiotic resistance. In GP this is a major problem with S. aureus which classically produces a penicillinase. Some staphylococci have been found producing β-lactamases with cephalosporinase activity as well. GN bacteria can express both chromosomal β-lactamases as well as plasmid mediated enzymes w/a wide variety of activities.
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(MID #409)
Mechanisms of resistance to penicillins: Permeability |
Expression of efflux pumps in both GN and in GP bacteria is a major cause of antibiotic resistance. The drugs are rapidly removed from the cell by an inducible pump system. In GN organisms, such as P. aeruginosa, there are >20 efflux systems that have been ID'd.
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(MID #410)
Discuss the Pharmacology of Penicillins |
The penicillins are charged molecules with distribution limited to the extracellular space. W/inflammation they can achieve bactericidal levels in the CSF and are used to treat meningitis. They are handled by the kidneys, primarily by tubular secretion and achieve high levels in the urine in patients with normal renal function. Each drug has different pharmacokinetic properties. Some biliary excretion (significant for nafcillin) and therapeutic levels are achieved in bile. Adverse effects that are most important include allergy, both immediate IgE-mediated hypersensitivity reactions that include anaphylaxis, and delayed responses such as rash.
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(MID #411)
Discuss the History of Cephalosporins |
Look and act much like penicillins. 6-membered dihydrothiazine ring w/substitutions at the #3 position generally affecting their pharmacological properties and changes at the #7 position affecting antimicrobial activity (more or less). Cephalosporin C has broad activity against both GP and GN bacteria, and was resistant to degradation by staphylococcal penicillinases (β-lactamases). But it did not cross the BBB and was ineffective against meningococcal meningitis. Since the cephalosporin nucleus is inherently stable to the penicillinases made by staphylococci, drugs were extremely helpful against S. aureus outbreaks in the 1950s. Derivatives were synthesized with more desirable properties: less painful to inject intramuscularly, longer half life (CEPHALOTHIN)
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(MID #412)
PROPERTIES OF CEPHALOSPORINS |
β-lactam class of antimicrobials. Activity is a function of their affinity for PBPs, their permeability properties, and their stability to β-lactamases. Cephalosporins, as a group, DO NOT BIND WELL to the PBP's of Enterococci, which are ENTIRELY RESISTANT to cephalosporins. Cephalosporins as a group are more potent inducers of the gram negative chromosomal β-lactamases, the members of the ampC family, which have cephalosporin activity. So if there are sizable populations of bacteria present, sub-inhibitory levels of cephalosporins may select out mutants with derepressed chromosomal β-lactamase activity resulting in clinical failure of therapy.
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(MID #413)
Discuss First Generation Cephalosporins: “House Cephalosporins” (1)CEFAZOLIN (parenteral) (2)CEPHALEXIN (oral) |
The development of cephalosporins is divided into 'generations.' These broad spectrum agents have excellent activity against community acquired bacteria: streptococci, many S. aureus, Enterobacteriaciae, E.coli, Klebsiella, and Proteus mirabilis. These drugs are rarely considered the drug of choice for a specific indication but they are often used for surgical prophylaxis, given immediately at the time of surgery, or for skin and soft tissue infections (but not bites). As more resistant GN infections became common and the importance of β-lactamase producing anaerobes in the bowel was appreciated, the use of 2nd generation cephalosporins increased.
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(MID #414)
Discuss Second Generation Cephalosporins (1)Cefoxitin (2)Cefotetan (3)Cefuroxime |
Cefoxitin and Cefotetan are very β-lactamase stable. Active against many aerobic and anaerobic Gram negative rods. Less activity against Gram positive organisms than first generation cephalosporins. Used primarily to treat infections arising from the bowel flora. DO NOT HAVE ACTIVITY against Enterococci (because they are cephalosporins and enterococci are resistant to all cephalosporins).
Cefuroxime (used orally and parenterally) retains excellent activity against many Gram positive bacteria, but has improved β-lactamase stability and is active against the Gram negatives in the respiratory tract such as Moraxellae and Hemophilus. Used to treat some respiratory tract infections. |
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(MID #415)
Discuss 3rd Generation Cephalosporins: (1)Cefotaxime (2)Ceftriaxone (3)Ceftazidime |
Cefotaxime and Ceftriaxone were developed to treat increasingly resistant GN rods in hospitalized patients. Due to enhanced activity, high blood levels, and pharmacokinetic properties, they enjoy widespread use against a number of common infections. Highly active against against pneumococci (penicillin-susceptible and most penicillin-resistant), Hemophilus, Meningococci, Gonococci, and many enteric GN bacteria. Both get into the CSF and with their intrinsic activity against the common causes of bacterial meningitis (S. pneumoniae and N. meningitides) are the agents of choice for presumed meningitis. CEFTRIAXONE is exceptionally active and is highly protein bound w/a LONG half-life. It can be given once (or twice) a day intramuscularly or intravenously for serious infections, making it ideal for many indications in an outpatient setting where compliance may be an issue (N. gonorrhoeae in unreliable patients) or when prolonged therapy may be needed as in CNS Lyme disease. CEFTAZIDIME is used for P. aeruginosa infection. Has the piperazine side chain present in piperacillin. Active against many other GN enteric and opportunistic pathogens, but has limited GP activity (compared to 1st generation cephalosporins or cefotaxime). It can induce chromosomal β-lactamases and should be used selectively.
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(MID #416)
Discuss Fourth Generation Cephalosporins: (1)Cefipime |
Cefipime has enhanced GP as well as GN activity and is used in settings where broad spectrum coverage is needed. It is also very active against P. aeruginosa and many of the opportunistic GN pathogens that are found in hospitalized patients.
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(MID #417)
Discuss CARBAPENAMS: (1)Imipenem (2)Meropenam (3)Ertapenem |
This family of β-lactam-like agents has LOST the β-lactam ring itself, while still acting much like penicillin or cephalosporin. They have high affinity for PBP2, which is present in low copy number and is an excellent target for the antibiotic. They have improved permeability properties. They can selectively use OprD, a porin channel that is not activated by the more common efflux pumps. Lack a β-lactam ring and are β-lactam stable. There have been organisms that have developed enzymes to break these agents down as well. These are very very broadly active drugs and it is easier to remember the organisms that are NOT killed: Stenotrophomonas and Burkholderia (opportunistic Gram Negatives) and ENTEROCOCCI. They can penetrate into the CSF. Imipenem is associated with CNS toxicity in patients with renal failure (seizures). Meropenem is less so.
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(MID #418)
Discuss MONOBACTAMS (1)Aztreonam |
Only activity against aerobic Gram negative rods!! Has a single ring and is stable to most β-lactamases but only binds to the PBP's of Gram negative bacteria. Can be used in penicillin allergic patients (since it has a different structure) and has the excellent safety profile of a β-lactam type antibiotic. Can be removed by efflux pumps that are expressed by some of the multi-resistant Gram negative pathogens.
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(MID #419)
Discuss resistance mechanisms to Cephalosporins |
Same as for the penicillins. Some species, notably the Enterococci, are inherently resistant to cephalosporins due to structural differences in their PBPs.
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(MID #420)
Discuss the Pharmacology of Cephalosporins |
Hydrophilic (do not enter phagocytic cells) and well distributed in the extracellular compartments. Wipe out the gut flora. Variably protein bound – with ceftriaxone being exceptionally highly protein bound, and have drug-specific half lives. Cefotaxime is metabolized and des-acetyl cefotaxime is excreted into the gut. Otherwise they are handled primarily by the kidney by tubular secretion and some glomerular filtration. First generation cephaloporins are good because they can be given orally, they can be used for surgical prophylaxis, and they taste good. The second generation cephalosporins are useful for community acquired infections, given orally/parenterally depending on the specific drug.
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(MID #421)
Discuss VANCOMYCIN |
Vancomycin has excellent activity against GP bacteria, particularly S. aureus. With emergence of methicillin resistant S. aureus and common occurrence of infection associated with indwelling intravenous catheters caused by coagulase-negative Staphylococci (not especially virulent skin flora that are inherently β-lactam resistant due to altered PBP's), vancomycin has become widely used. Vancomycin targets the cell wall, interacting w/the D-ala-D-ala portion of the pentapeptide side chain of Staph. Blocks both carboxypeptidase activity and transpeptidase. Vancomycin does not get into GN bacteria. Only active against Gram Positives so permeability is not an issue and there are no known bacterial enzymes that destroy the drug. Vancomycin is limited to Gram positives, Streptococci, Clostridia, Listeria, and Bacillus species as well as Staphylococci. It is active against the highly penicillin resistant strain of S. pneumoniae, and is used for pneumococcal meningitis until the susceptibilities of the infecting organism are known.
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(MID #422)
Discuss VANCOMYCIN RESISTANCE |
Resistance to vancomycin first developed in the enterococci. Reported in hospitals that used the drug orally exposing large populations of these commensal flora to selective pressure. Several genes mediate vancomycin resistance. Common gene enables bacteria to produce a D-ala-D-lactate dipsipeptide which thwarts vancomycin binding. Genes are most often found in Enterococcus faecium (VRE) and other enterococci. 25% of Enterococci are vancomycin-resistant. Major concern has been spread of these genes to Staphylococci. S. aureus resistant to vancomycin have been reported but are rare – have a REALLY thick peptidoglycan layer.
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(MID #423)
Discuss the Pharmacology of Vancomycin |
Drug is eliminated by the kidneys and doses must be adjusted in renal failure. 55% protein bound with a half life of 7 hrs (with normal renal function). Although vancomycin allergy is uncommon, rapid infusion of the drug is associated with “RED MAN” syndrome, a histamine mediated flushing of the face, neck, and trunk which may be associated with hypotension.
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(MID #424)
What are the classes of protein synthesis inhibitors? |
Macrolides/lincosamides, aminoglycosides (the only bactericidal class in this group), tetracyclines, chloramphenicol, streptogramins and oxazolidinones. These drugs are rarely drugs of choice for a particular infection or a particular bacterial species.
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(MID #425)
Discuss the Macrolides/Lincosamides |
The macrolides are safe bacteriostatic drugs originally used to treat community acquired infections. Erythromycin. 2nd generation called azalides with an extended spectrum of activity and different pharmacokinetics. Lincosamides are limited to clindamycin, a drug used for its anaerobic activity. Chemical structure: large 14-16 member lactone ring structure. MOA: Binds to 50S ribosomal subunit reversibly blocking binding of tRNA to the acceptor site, blocking translocation of the peptide chain. Macrolides are active against GP bacteria including streptococci, pneumococci, methicillin sensitive staphylococci. GN spectrum is limited but includes bordetella and campylobacter. Macrolides also have activity against mycoplasma, legionella, chlamydia and the treponemes. Azalides have an increased spectrum that includes activity against hemophilus species, Mycobacterium avium intracellulare (MAI), and depending on the azalide, increased activity against Gram positives (clarithromycin) or Gram negatives (azithromycin).
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(MID #426)
Discuss Resistance to Macrolides/Lincosamides. |
Bacteria may be macrolide resistant due to a permeability barrier (enterobacteriaceae). Active efflux pumps expel drug in Gram positive species. A single step mutation in the 50 rRNA gene can confer high level macrolide resistance in some species. Modification of the 50S rRNA subunit decreases erythromycin binding. This can be plasmid mediated.
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(MID #427)
Discuss Pharmacology of Macrolides/Lincosamides |
Macrolides are given orally. Not acid stable. Prepared with acid resistance coating. IV preps are available for more serious infections. The t ½ is 1.4 hrs. Considerably extended for azalides allowing for single or twice daily therapy. Family of agents achieves good distribution and achieves high intracellular concentrations (especially the azalides). Toxicity is limited. GI symptoms are more common with macrolides than azalides.
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(MID #428)
When are Macrolides/Lincosamides used? |
Community-acquired pneumonia: mycoplasma, legionella, chlamydia infections; pertussis, campylobacter gastroenteritis and MAI. Investigational role in use of these drugs as anti-inflammatory agents in CF and in the prevention of atherosclerotic cardiovascular disease.
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(MID #429)
Discuss the Aminoglycosides |
Bactericidal agents used for treatment of serious infections. Not used as single agents because of concerns about emergence of resistance. Used as empiric combination therapy for life-threatening infections. Used as combination therapy for resistant bacterial infections, and combination (synergy) therapy for enterococcal infections that require bactericidal activity. Narrow therapeutic to toxic ratio (serum level needed to be effective as a therapeutic agent is close to the level where drug toxicity is encountered). Consist of 2 amino sugars linked by glycosidic bonds to an aminocyclitol ring. Rapidly bactericidal agent with multiple MOAs. Primary target is 30S ribosome causing premature chain termination and RNA codon misreading. Causes leakage of outer membrane of Gram negatives. These drugs have significant toxicity. This includes nephrotoxicity in 5-25% of patients, ototoxicity including both cochlear and vestibular damage, and neuromuscular blockade. Drug levels are monitored in subjects w/renal disease.
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(MID #430)
Discuss Resistance to Aminoglycosides |
Aminoglycoside modifying enzymes. These enzymes such as the adenylyltransferases or phosphotransferases modify the aminoglycoside rendering them ineffective. Genes are often plasmid borne and so are readily transferred among different bacterial species. Additional mechanism of resistance is diminished uptake of the aminoglycoside via mutations in the electrochemical gradient.
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(MID #431)
Discuss the antibacterial spectrum of Aminoglycosides. |
Limited!! Active against Enterobacteriaceae, pseudomonas species, and Gram positive bacteria including staphylococci and streptococci. Some of the aminoglycosides are active against mycobacteria. No activity against anaerobes.
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(MID #432)
Discuss the Tetracyclines |
Large family of broad spectrum, bacteriostatic agents that have a limited but important role. Their principal role is for treatment of Lyme disease, community-acquired pneumonia, and acne. 4 fused 6-carbon rings. Mechanism of action: primary target is the 30S ribosome, preventing binding of aminoacyl tRNA to the acceptor (A) site on mRNA. These drugs have GP activity, including pneumococcus, streptococci, and enterococci, but they are rarely used because of resistance. They have activity against gram negatives, E.coli but not other Enterobacteriaceae, Neisseria, Hemophilus and some Shigella. Active against mycoplasma, rickettsia, legionella, spirochetes, and chlamydia.
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(MID #433)
Discuss Resistance to Tetracyclines |
The primary mechanism of resistance to tetracyclines is decreasing penetration or increasing export of the drug via an efflux pump. This mechanism may be plasmid-mediated and confers resistance to all members of the class.
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(MID #434)
Discuss toxicity of Tetracyclines as well as pharmacology. |
Most tetracyclines are administered orally. Short and longa cting agents. Most are lipophilic and have excellent tissue distribution. Most commonly used tetracyclines are minocycline (metabolized in the liver) and doxycycline (inactivated in the intestine) are cleared by nonrenal routes. Generally well tolerated but there is a long list of potential side effects, including photosensitivity, discoloration of children's teeth, hepatotoxicity and hypersensitivity reactions.
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(MID #435)
Discuss Chloramphenicol |
Broad spectrum agent, single member of its class. It achieves high concentrations following oral administration including in the CSF. Has activity against agents that cause meningitis including pneumococcus, hemophilus and neisseria. Binds to the 50S ribosome preventing attachment to the acceptor (A) site on mRNA. Chloramphenicol causes a dose related bone marrow depression and rarely aplastic anemia that is idiosyncratic. In neonates the gray baby syndrome was a concern.
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(MID #436)
Discuss Streptogramins |
Combo of 2 drugs derived from pristinamycin. First is quinupristin and 2nd is dalfopristin. Protein synthesis inhibitors working at the 50S ribosomal subunit. Combo is used exclusively to treat GP infections including vancomycin resistant enterococci (E. faecium) and complicated methicillin resistant S. aureus (MRSA) infections where vancomycin cannot be used. Resistance has occurred primarily by ribosomal modification (methylation). Can be plasmid mediated. Drug is bactericidal if the isolate is macrolide susceptible. It is only available parenterally. Toxicity includes phlebitis at the infusion site and myalgias which can be quite bothersome.
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(MID #437)
Discuss Oxazolidinones (Linezolid) |
Linezolid is the sole member of this new class of bacteriostatic agents. This family of drugs is active at the 50S ribosomal subunit and inhibits formation of the initiation complex. Active against GP bacteria including MRSA and all vancomycin resistant enterococci. It has the pharmacological advantage of being available both orally (with excellent absorption) and parenterally. Resistance has been described occurring by mutation of the ribosomal binding site. The drug is well distributed and well tolerated. Thrombocytopenia and myelosuppression have occurred with prolonged administration (> 2 weeks therapy).
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(MID #438)
Discuss Quinolones |
Quinolones can be administered orally and parenterally. Active against a broad spectrum of bacteria (bactericidal) including a number of common nosocomial pathogens. Used for empiric treatment of community acquired pneumonia, infectious diarrhea, and STDs. Also used for treatment of serious infections caused by susceptible pathogens. Some of the quinolones have activity against Mycobacteria tuberculosis and have been used in combo therapy to treat drug-resistant TB. Quinolones have limited toxicity. They have a bicyclic aromatic core. Ring structures vary depending on the cmpd but the derivatives are still referred to as quinolones. Alterations of the basic ring structure and side chains alter the activity and pharmacology of the agents.
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(MID #439)
Discuss MOA and Mechanism of Resistance to Quinolones |
MOA: Bactericidal. Several sites of action. (1) They bind DNA-DNA gyrase (topoisomerase II) complex and block further DNA replication. (2) They block topoisomerase IV interfering with the separation of interlocked, replicated DNA molecules. (3) There appear to be other, as yet undefined, mechanisms of killing that may involve RNA and protein synthesis.
Because of the widespread use of these drugs, quinoline resistance is a major problem. Resistance can emerge by mutations in the topoisomerase II or IV genes. Several active efflux pumps have been demonstrated in both GN and GP bacteria. Resistance can emerge during therapy. |
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(MID #439)
Discuss the antibacterial spectrum of Quinolones: |
Varied. First generation drugs (nalidixic acid) are active only against Gram Negs. The 2nd generation drugs (fluoroquinolones) have enhanced coverage against pseudomonas and also have GP activity including Staphylococcus. The newer agents, 3rd generation quinolones, have activity against the above agents as well as legionella, mycoplasma and some include the anaerobes.
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(MID #440)
Discuss the pharmacology and toxicity of Quinolones. |
Well absorbed orally. Most can be administered parenterally. Can switch from parenteral to oral therapy which is an advantage. Extremely well distributed achieving high concentrations in most tissues and fluids. CSF concentrations are lower than the serum. One additional advantage of these cmpds is their ability to achieve high intracellular concentrations, thus enhancing their activity against intracellular pathogens. Most quinolones are eliminated by the kidneys.
Toxicity: Quinolones are well tolerated. Allergic rxns including fever and rash can occur. Photosensitivity can occur especially with quinolones having a fluorine or chloride at the C8 position. GI and CNS effects as well as tendinitis are also described. |
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(MID #441)
Discuss Structure of Trimethoprim-Sulfamethoxazole |
Fixed drug combination, combines 2 cmpds that block folate synthesis. Trimethoprim is a pyrimidine synthesized as a dihydrofolate reductase inhibitor with the goal of sequentially inhibiting folate synthesis by potentiating sulfa activity. Sulfamethoxazole is a paraaminobenoic acid (PABA) inhibitor. Sulfur atom must be linked to the benzene ring for antimicrobial activity. A free amino group at the C4 position is associated w/enhanced activity. Substitutions at the N1 position change pharmacological and antimicrobial properties of the cmpd.
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(MID #442)
Discuss Mechanism of Action (MOA) and Mechanism of Resistance to Trimethoprim-Sulfamethoxazole |
Sequential inhibitors of folic acid synthesis. Sulfamethoxazole is a structural analog of PABA and competes for the enzyme dihydropteroate synthetase. Results in reduced dihydropteroic acid available for the 2nd step in the folate synthesis pathway. Trimethoprim is a competitive inhibitor of the enzyme dihydrofolate reductase, the next step in the biosynthetic pathway. Mammalian cells do not synthesize folate – they require preformed folate.
The frequency of resistance to Trimethoprim-Sulfamethoxazole was initially low because of the need for more than one mutation. Resistance has increased over the years. For sulfamethoxazole, resistance occurs as the result of decreased permeability or increased production of PABA. For trimethoprim, resistance develops due to the synthesis of an enzyme w/altered affinity for TMP or by the overproduction of dihydrofolate reductase. |
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(MID #443)
Discuss Antibacterial spectrum of TMP-SMZ |
Broad-spectrum antimicrobial agent. Has activity against Gram negs including E.coli, Klebsiella, Vibrio, Shigella, Neisseria, and H. influenzae. Also active against Gram Positives including Staphylococci, Streptococci, Listeria, but NOT Enterococci. TMP-SMZ has activity against pneumocystis, nocardia, malaria, and chlamydia. Used for treatment of UTI, prostatitis, and diarrheal diseases. Increase in resistance over the past 10 yrs. Drug of choice for treatment of Pneumocystis Carinii pneumonia in HIV-infected subjects. Also useful in selected miscellaneous infections caused by nocardia and B.cepacia.
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(MID #444)
Discuss Pharmacology and Toxicity of TMP-SMZ |
TMP-SMZ is combined in a 1:5 ratio that gives a serum ratio of 1:20. Optimal ratio for synergistic activity. Agent is available both orally and parenterally and achieves excellent tissue distribution including the lungs, kidneys, prostate, biliary tree and CNS.
There is a long list of potential side effects. Most common toxicity (~5%) is hypersensitivity rxns including fever and rash. Rash can be severe in rare cases progressing to life-threatening Stevens Johnson syndrome. Other side effects include GI symptoms and rarely megaloblastic anemia or renal insufficiency. |
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(MID #445)
METRONIDAZOLE |
Agent has a broad range of activity that includes anaerobic bacteria as well as a variety of parasites. Low MW nitroimidazole. MOA: Reduction of metronidazole following uptake by bacteria results in release of intermediate products. These products or free radicals damage DNA as well as other cellular macromolecules. Bactericidal against susceptible bacteria. MOR: Resistance is rare due to need for multiple steps to be altered for resistance to emerge. Resistance is conferred thru reduction in pyruvate: ferredoxin oxidoreductase activity, which limits cellular uptake of metronidazole and subsequent activation. ANTIBACTERIAL SPECTRUM: Most gram negative anaerobes including bacteroides. Some GP anaerobes: clostridia (C. difficile). Also Gardnerella vaginalis, Helicobacter pylori, Richomonas vaginalis, giardia. INDICATIONS FOR USE: Used for parasitic infections such as trichomonas, giardia, also for anaerobic infections such as bacteroides infections, C. difficile associated diarrhea, and peptic ulcer disease associated with H. pylori.
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(MID #446)
Discuss Metronidazole Pharmacology and Toxicity. |
PHARMACOLOGY: Can be administered orally, parenterally, vaginally, and rectally. Extremely well-distributed including the CNS. T ½ 8 hrs. Metronidazole and most metabolites are excreted in the urine.
TOXICITY: Generally well tolerated. Can cause nausea and vomiting, rarely CNS symptoms. Disulfiram effect with alcohol. Interferes with metabolism of warfarin (anticoagulant). Not used in pregnancy due to concern for mutagenicity (not proven). |
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(MID #447)
Discuss DAPTOMYCIN |
Has activity against antimicrobial resistant GP bacteria. A new class of antibiotic: 13 member amino acid cyclic lipopeptide with a decanoyl tail. MOA: Bactericidal antibiotic inserts into the bacterial cell membrane, causing membrane depolarization and potassium efflux. Results in loss of cell viability. MOR: Clinical isolates w/reduced susceptibility to daptomycin have been reported but the mechanism of resistance is uncertain. ANTIBACTERIAL SPECTRUM: Active against GP including staphylococci, pneumococci, and enterococci. PHARMACOLOGY: Only available parenterally. T ½ 9 hrs. Cleared via the kidney. Does not achieve adequate levels in the lung to treat pneumonia. TOXICITY: GI problems, concerns about muscle discomfort, increased CPK. INDICATIONS FOR USE: Resistant Gram Positive bacterial infections such as MRSA (methicillin resistant staph aureus) or VRE (vancomycin resistant enterococci). Used for skin/soft tissue infections, endocarditis, bacteremias.
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(MID #448)
Name 3 ways in which bacteria become resistant to antibiotics! |
(1)Development of point mutations in one of the target genes (micro-evolutionary change). Alterations in the beta-lactamase gene extending its spectrum of activity against different beta-lactam antibiotics.
(2) Macro evolutionary changes including rearrangement of genes as might occur with the acquisition of antibiotic resistance bearing plasmids or transposons. (3) Final way is to acquire DNA from an exogenous source. For example, naturally transformable species such as Neisseria can acquire DNA from the environment. It is believed that this is the way Neisseria species acquired antibiotic-resistance genes (e.g., penicillin). |
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(MID #449)
Define: Cross Resistance and Co Resistance to antibiotics. |
CROSS RESISTANCE: A single resistance mechanism confers resistance to an entire class of antibiotics. (Aminoglycoside-modifying enzymes may confer resistance to several members of the aminoglycoside family). Cross-resistance can also occur across different classes of agents, either as a result of overlapping drug targets (macrolides & lincosamides) or if there is a drug efflux pump with a broad range of activity (capable of exporting different classes of drugs.)
CO RESISTANCE: Presence of resistance to more than one class of antibiotics in the same bacterial strain as might occur on a plasmid. |
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(MID #450)
Define Co-Selection with regard to antimicrobial resistance. |
Selection of multiple antibiotic resistance genes when one of these genes is selected. Integron: cassette of antibiotic-resistance genes under the control of a single promoter. Genes are expressed in a coordinate manner, although the most downstream gene may not be as efficiently expressed as the gene next to the promoter. Cassettes are found in both GP and GN bacteria. Since they are a form of transposon they can become a part of the bacterial chromosome or plasmid and can then be transmitted among different strains.
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(MID #451)
Mechanisms of Antimicrobial Resistance: (1)Enzymatic Modification (2)Decreased Accumulation of Antibiotic (3)Alteration of the Drug Target |
(1)Enzymatic Modification: Bacteria elaborate enzymes that are capable of modifying or destroying the antibiotic before it reaches its target. Β-lactamases elaborated by GP and GN bacteria hydrolyze the amide bond of the Β-lactam nucleus destroying the antimicrobial activity of the agent. These enzymes have differing specificities that make them either relatively selective or broad ranging in their target. May be constitutively expressed or induced to express on exposure to a Β-lactam.
(2)Decreased Accumulation of Antibiotic: Penicillin is unable to penetrate the outer membrane of GN bacteria and so is ineffective against GN bacteria. (3)Alteration of the Drug Target: Modification of the cellular target for an antibiotic is another mechanism of resistance. Vancomycin lost activity against enterococci when the cell wall precursor that it bound was modified so that vancomycin was no longer able to attach to that site. |
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(MID #452)
Discuss Methods for the Dissemination of Antibiotic Resistance Genes: (1)Clonal Spread of A Resistant Strain (2)Plasmid Transfer (3)Free DNA (4)Bacteriophage |
(1)Clonal Spread Of A Resistant Strain: Under selective pressure of antibiotics a strain carrying antimicrobial resistance genes may be preferentially selected and transferred within a population.
(2) Plasmid Transfer: Plasmids carrying one or multiple antibiotic resistance genes can be transferred among different bacterial strains or species by conjugation or transduction. (3) Free DNA: Naturally transformable species such as pneumococcus can acquire native DNA from the environment. Recombination events then integrate this genetic material into the chromosome. This is how pneumococci acquired penicillin resistance. (4) Bacteriophage: Transduction may be a means of transfer of both antimicrobial resistance genes as well as genes conferring virulence. |
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(MID #453)
Discuss the Epidemiology of Transmission of Antimicrobial Resistance Mechanisms |
(1)Transmission of resistance genes within the community is increasingly common. Kids attending day care, adults in nursing home facilities, and patients recently discharged from hospitals all act as reservoirs, serving as potential vectors of spread of resistant bacteria. Increasing use of antimicrobials within the community provides selective pressure for preservation of these isolates. (2) Animals raised on farms where antibiotics are used as growth factors are a huge source of antibiotic resistance. The quantity of antibiotics used in healthy animals far exceeds the quantity used for therapy of bacterial infections in humans. (3) International travel allows subjects visiting foreign countries to acquire uniquely resistant strains in a particular locale and transport them back to the US. MRSA and penicillin resistant pneumococci have been transmitted in this manner. (4) In the hospital, proximity of patients to one another, their immunocompromised status, their exposure to numerous healthcare workers and the frequent need for broad spectrum antibiotics set stage for emergence of the most resistant strains. Can be transferred from patient to patient.
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(MID #454)
Methods to Reduce the Spread of Antimicrobial Resistant Bacteria |
(1)Eliminate use of antibiotics in animal feed.
(2)Observe strict infection control policies in the hospital setting. (3)Reduce inappropriate prescribing of antibiotics in the community (e.g., for the treatment of upper respiratory tract infections). (4)Antibiotic restriction policies in the hospital setting. |
