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330 Cards in this Set

  • Front
  • Back
Bacterial chromosomes are found in what structure? Why is this structure given its name?
Nucleoid. The nucleoid has no membrane as does the nucleus of a mammalian cell.
What structure is unique about bacterial cell walls?
Peptidoglycan (also called mucopeptide).
What antibiotic targets the enzymes that are responsible for the synthesis of peptidoglycan molecules?
Penicillin and its derivatives.
Why are ribosomes of bacteria targets for antibiotics?
The prokaryotic (bacterial) ribosome has a different structure than the eukaryotic (man) ribosome therefore the drugs will not affect eukaryotic cells and will be selective for bacteria.
Why is it important to perform a Gram stain in some clinical situations?
The Gram stain aids in the identification of bacteria by aiding in their visualization (size and grouping) and dividing them into two major groups (Gram+ and Gram-). Examination of the gram stain allows for a rapid presumptive diagnosis in some clinical situations.
What color do Gram+ bacteria appear after Gram staining?
Purple-black. Some people say they are blue.
What color are Gram-negative bacteria after Gram staining?
Pink to red.
What is the term used to describe round bacteria?
What is the term applied to bacteria that are long and narrow?
Bacilli or rods.
Some bacteria appear to have round forms and rod-shaped forms. What is the term applied to this morphology?
What term is applied to bacteria that appear to be narrow rods that curve?
When a bacterial population contains microorganisms that vary in their size and shape, it is said to be?
Cocci are usually arranged into one of four different types of groupings. Name these four groupings.
Single. Pairs (or diplococci). Clusters. Chains.
Gram-positive rods may appear in picket fence-like arrangements or in arrangements resembling Chinese letters. What is this grouping called?
Which bacterial species is a Gram-positive coccus arranged in grape-like clusters?
Which bacterial species is a Gram-positive coccus arranged in chains?
Which bacterial species is a Gram-negative coccus (kidney bean shaped) in pairs?
Which anaerobic bacterium is a Gram-positive rod that forms spores?
Which Gram-positive rod forms palisade arrangements?
What is the Gram stain and morphologic characteristics of E. coli?
Gram-negative rod.
What is the Gram stain and morphologic characteristic of Klebsiella?
Gram-negative rod.
What genus of bacterium is characterized by its spiral shape?
What portion of the bacterium constitutes the cell wall?
That portion that lies between the cell membrane and the capsule (if present).
What are the main constituents of the Gram-positive cell wall?
Peptidoglycan and associated polymers (Teichoic and lipoteichoic acids and some proteins).
What is the composition of the Gram-negative cell wall?
Peptidoglycan layer and outer membrane.
What is the difference in the peptidoglycan layer of Gram-positive and Gram-negative bacteria?
There are fewer cross-linkages and numbers of peptidoglycan layers in Gram-negative bacteria than in Gram-positive bacteria.
What is lysozyme?
An enzyme found in a variety of body fluids that can cleave the peptidoglycan of bacterial cell walls.
What does the process of transpeptidation do during synthesis of bacterial cell walls?
It cross-links one peptidoglycan chain with another causing the formation of a mesh.
What is the mechanism of action of penicillins and cephalosporins?
They inhibit transpeptidation of the peptidoglycan layer of the cell wall by interfering with the transpeptidase enzyme.
What type of microorganisms are referred to as L-forms?
Bacteria that have lost their cell walls. This can be natural (Mycoplasma, Ureaplasma) or artificially formed due to exposure to penicillin. These organisms are not susceptible to penicillin because they have no cell wall.
What cell wall constituent is unique to Gram-positive organisms?
Teichoic acids.
What morphological feature is unique to Gram-negative bacteria?
The outer membrane (also called periplasmic membrane).
What are the functions of the outer membrane of Gram-negative bacteria and the periplasmic space between the outer membrane and the cell wall?
Outer membrane resists the action of detergents. Periplasmic space provides a location for accumulation of several types of secreted proteins.
What molecule of Gram-negative bacteria largely replaces phospholipids in the outer membrane of the organism?
Lipopolysaccharide, LPS (also called endotoxin)
Name the three regions of the bacterial lipopolysaccharide (LPS) molecule.
Lipid A - embedded in the outer membrane. Core. O antigen. Responsible for serotypes within a species.
What part of the LPS molecule is responsible for its toxicity?
Lipid A
Of patients who develop sepsis due to a Gram-negative infection, how many will die per year?
300,000 (40-60% of the patients).
What is the function of the cytoplasmic membrane of a bacterium?
Site of active transport. Site of electron transport and oxidative phosphorylation. Site of synthesis of cell envelope layers (peptidoglycan, outer membrane) and capsule.
How many chromosomes does a bacterium have.
One. 1-3 copies may be present at any one time.
What is the function of the nuclear region of the bacterium.
Gene expression including DNA replication, transcription and translation.
What structure allows bacteria to be motile?
What is the term for a single flagellum at one end of the bacterial cell?
What is the term for flagella that are found to be located all over the cell?
What is the process whereby flagella propel bacteria up a concentration gradient?
Spirochetes move by means of a specialized flagella. What is this called?
Axial filament.
What are pili?
Short hair-like projections on bacteria. They are used for attachment to host cells and/or for twitching motility. Pili are often virulence factors.
What is the specialized structure used by Gram-negative bacteria to exchange genetic material?
Sex pilus.
What is the chemical make-up of the capsule of a bacterium?
Polysaccharides or polypeptides.
What is one of the main functions for the capsules of bacteria?
They are anti-phagocytic. Some may enable to bacterium to attach to surfaces.
When do bacteria make spores?
When the environmental conditions are harsh and not conducive to vegetative growth.
Why is it difficult to rid instruments/ products of bacterial spores?
They can exist for prolonged periods of time and are resistant to physically and chemically harsh conditions.
What types of bacteria grow in a temperature range from 15 - 40 C?
What type of bacteria grow at temperatures of 60 to 80 C and above?
What type of bacteria grow at 5 - 10 C?
Some bacteria will not grow without oxygen while others will not grow in the presence of oxygen. What are these two types of bacterial called?
Obligate aerobes - require oxygen. Obligate anaerobes- oxygen is toxic to these organisms.
What is the replicative process used by bacteria and what type of rate of growth characterizes them?
Binary fission. Exponential growth.
What stage of growth occurs after transfer of bacteria from an old culture into a new culture?
Lag phase growth.
During which phase of growth are bacterial actively utilizing nutrients and exhibit a maximum growth rate?
Log or exponential.
What is the phase of growth that occurs when certain essential nutrients become limiting in a bacterial culture?
Stationary phase.
What phase of growth occurs when bacteria are held in stationary phase for a long time?
Death phase.
What is a disinfectant?
An agent that eliminates infection by killing vegetative cells.
What is an antiseptic?
Prevents sepsis by inhibiting or arresting the growth of microorganisms.
What does the term "sterilize" mean?
A process that kills all forms of life (vegetative cells and spores are included).
What does sanitize mean?
The microbial flora has been reduced (99.9% of organisms killed) and is judged safe by public health officials.
What methods can be used to sterilize?
Autoclave - 15 min, 121 C, 15 psi Filtration through 0.22 micron pore size filter (retain bacteria not viruses). Radiation - usually gamma rays Ultraviolet radiation - good for surfaces. Ethylene oxide - industrial use.
What is the phenol coefficient?
The ratio of the highest dilution of the disinfectant that kills all of the bacteria in 10 minutes but not 5 minutes as compared to the dilution of phenol that achieves and same effect.
Do soaps kill bacteria?
No. They help remove bacteria.
What type of antiseptic is best for hand disinfection?
Those that are alcohol based.
Which halogens are used as antibacterial agents?
Iodine: iodinates proteins on bacteria. Chlorine: 10% chlorox used to clean surfaces in labs. Treatment of water.
What is an antimicrobic?
Includes antibiotics and synthetically derived antimicrobial agents. Antibiotics are often produced by fungi while some antibacterial agents are synthesized.
What does the term specific toxicity mean when applied to an antimicrobic?
An agent that will kill the microorganism without harm to the host.
What type of antimicrobic will kill bacterial cells without aid from the immune system of the host?
What type of antimicrobics inhibit bacterial growth but do not kill the bacterium?
What is meant by the "minimum inhibitory concentration" (MIC)?
The amount of the antimicrobic that inhibits growth under standard laboratory testing.
What type of spectrum do antimicrobics have that are restricted to specific classes of microbes?
Narrow spectrum.
What is the spectrum of antimicrobics that affect a wide range of bacteria (Gram-negative and Gram-positive)?
Broad spectrum.
What two types of resistance do bacteria exhibit against antimicrobic agents?
Innate: The bacterium lacks the target for the antimicrobic or has a structural feature that prevents the antimicrobic from reaching its target. Acquired: A mutation has affected the target for the antimicrobic or the bacterium can produce an enzyme that degrades the antimicrobic.
What is the therapeutic index of an antimicrobic?
Ratio of the dose that is toxic to the host to the dose that is effective against the infection.
What is an antimetabolite?
A substance that mimics a normal metabolite and interferes with its metabolic pathway.
What is the mode of action of sulfa drugs?
Inhibit the enzyme dihydropteroic acid synthetase that catalyzes the condensation of dihydropteridine and PABA.
Give an example of a sulfa drug.
Are sulfa drugs bacteriostatic or bacteriocidal?
What is the basis of the specific toxicity of sulfa drugs for bacteria?
Humans do not synthesize folic acid and bacteria do.
What is the mechanism of action of isoniazid?
Appears to interfere with lipid synthesis.
What is the mechanism of action of para-aminosalicylic acid (PAS)?
The same as for sulfa drugs. Inhibit dihydropteroic acid synthetase.
What is the mechanism of action of sulfones such as dapsone?
Same as sulfa drugs. Inhibit dihydropteroic acid synthetase.
What is the mechanism of action of trimethoprim?
Inhibits folic acid biosynthesis. Inhibits dihydrofolate reductase.
What does the term "synergy" mean in regard to antimicrobics?
The combined effect of both drugs is greater than that achieved which either are used alone.
What is the mechanism of action of nitrofuran?
Appears to inhibit initiation of protein translation in both Gram-positive and Gram-negative bacteria.
What is the bacterial target for penicillins and other beta lactams?
The peptidoglycan of the bacterial cell wall.
Why are beta lactams only effective on growing cells?
Because they inhibit the formation of the cell wall, the cell must be synthesizing new peptidoglycan.
Are penicillins bactericidal or bacteriostatic?
What has been modified on synthetic penicillins to make them effective against Gram-negative organisms?
The R group attached to the beta lactam ring.
Why are Gram-negative bacteria generally more resistant to penicillins?
The antibiotic does not readily cross the outer membrane of Gram-negative organisms.
Why have some bacteria developed a resistance to penicillin?
They make a beta-lactamase enzyme that breaks penicillin down into an inactive form. Others have altered penicillin binding proteins that prevent penicillin from affecting the cell.
What antibiotic can be given with penicillin to inhibit beta lactamase enzymes?
Clavulanic acid.
Why have the R group of penicillin been altered by the pharmaceutical industry?
To develop drugs that are effective against Gram-negative organisms. To facilitate oral administration of the drugs.
What is the mode of action of the cephalosporins?
Similar to penicillin. Inhibit formation of the peptidoglycan layer of the bacterial cell wall.
Why to carbapenems and monobactams inhibit cell wall synthesis of bacteria?
They both have a beta lactam ring and therefore function as does penicillin.
What is the mechanism of the antimicrobic D-cycloserine?
Inhibits peptidoglycan formation in the cell wall.
What is the mode of action of vancomycin?
Interferes with the bactoprenol lipid carrier that facilitates assembly and transport of the peptidoglycan to the outside of the bacterial cell.
What is the mode of action of bacitracin?
Inhibits transport of the peptidoglycan to the outer surface of the bacterium.
What is the mode of action of streptomycin?
Affects protein synthesis by binding to the 30s ribosome inhibiting initiation of translation.
What accounts for resistance that bacteria may develop to streptomycin?
They produce an enzyme that modifies streptomycin.
What is the major toxicity associated with the use of streptomycin?
Toxic to the 8th cranial nerve.
What is the mode of action of other aminoglycosides besides streptomycin?
Similar to streptomycin.
Is tetracycline bacteriostatic or bacteriocidal?
What is the mode of action of tetracycline?
Binds to the 30S ribosome and prevents binding of aminoacyl-tRNA to the 30S ribosome thereby inhibiting protein synthesis.
Why are eukaryotic cells not affected by tetracycline?
Eukaryotes do not have the transport system that facilitates entry of tetracycline into the cell.
Name three resistance mechanisms known for the action of tetracyclines on bacteria.
Efflux of tetracycline by a specific protein. Protection of the ribosome binding site for tetracycline by an additional protein. Modification of tetracycline by an enzyme.
Which antibiotics affect the 50S ribosome of bacteria?
Chloramphenicol Erythromycin Lincomycin Clindamycin Oxazolidinones
Is chloramphenicol bacteriostatic or bacteriocidal?
What is the mechanism of action of chloramphenicol?
Binds to the 50S ribosome and inhibits peptide bond formation.
What accounts for bacterial resistance to chloramphenicol?
An R-factor produces an enzyme that inactivates the drug.
Is erythromycin bacteriostatic or bacteriocidal?
What is the mode of action of erythromycin?
Inhibits the peptidyl bond transferase reaction.
What accounts for bacterial resistance to erythromycin?
An altered protein of the 50S ribosome will not allow the drug to bind.
What is the mode of action of lincomycin?
Binds to the 50s ribosome.
What is the mode of action of clindamycin?
Binds to the 50s ribosome.
What is the mode of action of linezolid?
Appears to interact with the 50S ribosome and the 23S RNA.
What types of bacteria are sensitive to linezolid?
Gram-positive bacteria (especially Staphylococci, Streptococci and Enterococci).
What is the mode of action of nalidixic acid?
Inhibit the DNA gyrase of bacteria.
What types of infections can be treated with metronidazole?
Protozoan and anaerobic bacteria.
What antibiotic interferes with RNA synthesis?
What types of antimicrobics affect the cell membrane?
Amphotericin B Nystatin Imidazoles Triazoles Polymyxins.
What is the basis of toxicity of amphotericin B for fungal cells?
Binds to cell membranes that contain sterols (ergosterol). Mammalian cell membranes do not contain ergosterol.
What is the mechanism of action of ketoconazole and what types of organisms are sensitive to it?
Interferes with the biosynthesis of ergosterol. Active against fungi which have ergosterol in their cell membrane.
What is the mechanism of the polymixins and what type or microbes are sensitive to it?
Binds to membranes lacking sterols. Active against Gram-negative bacteria.
What is the meaning of "selective pressure" as applied to the growth of microorganisms?
Growth in an adverse environment.
What does the term "selective advantage" mean in regard to growth of microorganisms?
Growth in an adverse environment.
What are the consequences of genetic change in bacteria?
Development of low-level antibiotic resistance Acquisition of extrachromosomal DNA elements that confer high-level antibiotic resistance. Spread of disease-causing traits (virulence traits) or antibiotic resistance. Physical linkage of new genetic determinants that can be transmitted to other bacteria. Variation that allows organisms to escape the human immune system.
What does a promoter do?
A signal sequence in DNA that tells RNA polymerase where to initiate transcription.
What is a transcription initiation site?
The site on the DNA molecule where transcription actually begins.
What is the coding sequence of a gene?
The sequence of nucleotides that carry the information prescribing the amino acid sequence of proteins.
What is a transcription termination site?
A sequence in DNA that tells RNA polymerase to stop copying mRNA from the DNA template.
What is a mutation?
An alteration in the nucleotide sequence of DNA.
Name two different types of mutations?
Mutations in the code for the amino acid sequence of a protein. Mutations that change the information used to regulate protein expression.
When do mutations occur in the DNA sequence?
During synthesis of DNA. During repair of DNA damage.
What is the name of a mutation that results from a change in one base of the nucleotide sequence?
A point mutation.
What is the term applied to a mutation that alters the coding sequence of a gene but does not alter the amino acid sequence of the protein produced from that gene?
Silent mutation.
What is a missense mutation?
The mutation leads to placement of an "incorrect" amino acid in the protein product of the gene.
What is the name of a mutation that results in placing a stop codon in the middle of a gene?
Nonsense mutation.
What type of mutation results from deletions or insertions of one or more bases in the nucleotide sequence of a gene?
Frameshift mutations.
Two microorganisms utilize frameshift mutations to change their antigenicity. What bacteria do this?
Neisseria meningitidis and Neisseria gonorrhoeae.
What is the name given to reiterations of a segment of DNA within the chromosome?
What is the name for the exchange of genetic material that results from uptake of "naked" bacterial DNA?
What is the name applied to exchange of genetic material between bacteria by a bacteriophage particle?
What are bacteriophage?
Obligate intracellular parasites of bacteria.
What are the four stages that occur during infection of a bacterium by a bacteriophage?
Adsorption. Penetration. Intracellular replication. Release - by lysis.
What are the three stages of intracellular replication of a bacteriophage?
Early stage - viral encoded proteins are produced to control host metabolism. Middle stage - viral nucleic acid replication. Late stage - synthesis of viral structural proteins and construction of progeny phage.
What assay is commonly used to identify and grow bacteriophage?
Plaque assay.
What type of genetic exchange occurs when bacterial DNA is mistakenly inserted into a bacteriophage?
Generalized transduction.
What is a temperate bacteriophage?
A phage that can follow a lytic infectious cycle or become quiescent (non-functioning) in the host cell.
When a bacteriophage is nonfunctioning in the host cell it is said to be in what state?
In the lysogenic state.
What is the name given to a phage that is in the lysogenic state?
It is a prophage (or lysogen).
Name two different mechanisms used by phage to become lysogenic?
Incorporate into the chromosome of the bacterial cell. Exist in the cytoplasm of the bacterial cell as an episome (or plasmid).
What is the name of the mechanism whereby the bacteriophage comes out of the lysogenic state?
How can lysogenic bacteriophage change the genetic material of bacteria?
Alter virulence factors. Transduce a specific fragment of bacterial DNA that is physically linked to the bacteriophage DNA - results from imprecise excision of the phage from the bacterial DNA.
What is the process of genetic exchange that requires cell-to-cell contact between donor and recipient bacteria?
What is a plasmid?
An extrachromosomal genetic element that is not part of the bacterial chromosome. They are usually circular DNA molecules.
What types of genetic information do plasmids usually convey to a bacterial cell?
Genes that confer a selective advantage.
How do conjugal plasmids transfer genetic information between bacterial cells?
Contact between the two bacteria occurs by physical interaction via a sex pilus. The plasmid uses this structure to move into the new bacterial cell.
What types of genes are carried by conjugal plasmids?
Antibiotic resistance. Virulence traits: toxins, colonization factors, physiologic functions.
What is a mobilizable plasmid?
A molecular "parasite" that uses the conjugal apparatus of another plasmid to transfer between bacterial cells.
How can a plasmid promote the transfer of a bacterial chromosome?
Integration of the plasmid into the bacterial chromosome allows conjugally mobilized movement of the chromosome into a recipient cell.
What is the name applied to an extrachromosomal conjugal plasmid that carries bacterial chromosomal genes?
F' (F-prime) plasmid.
How does an F' plasmid form?
When it excises from the bacterial chromosome, imprecise excision causes the plasmid to pick up a piece of host cell DNA.
What is the name given to linear pieces of DNA that can move from one replicon to another?
Is DNA homology required between the original integration site of a transposon and the target site to which the transposon moves?
How do transposons move from one bacterial cell to another?
They can not do this by themselves. They transfer when the DNA in which they reside is introduced into a bacterial cell.
Transposons contribute to what types of genetic exchange and variation?
Transfer of antibiotic resistance. Transfer of virulence determinants. Catalysis of conjugation.
What is a parasite?
A small plant or animal that lives within or on a larger organism of a different species.
What is the name for an organism that is parasitized by a smaller organism?
The host.
Define infection.
Entrance and growth of a parasite in a living host regardless of the effect on the host.
What is the name applied to the cause of a specific disease?
Etiologic agent.
What is a parasite that causes disease in a susceptible host?
What is a pathogen that causes disease in compromised hosts?
Opportunistic pathogen.
What are the three results of exposure of a host to microorganisms?
Eradication. Inapparent infection. Infectious disease with recovery or death.
What four types of inapparent infection may occur in a host exposed to a microorganism?
It becomes part of the normal flora. The host becomes a healthy carrier. A latent infection is established. A persistent infection is established.
What is meant by the incubation period of an infectious disease?
The period from exposure to the development of symptoms.
What is the prodrome of an infectious disease?
The period when the first symptoms of the disease appear.
What is the period called when all of the symptoms of a disease have become manifest?
The syndrome.
What type of infection occurs when there is a balance between host response and virulence traits of an infectious disease?
Inapparent infection.
What happens when host responses are overcome by the virulence traits of an infectious microorganism?
Infectious disease.
What is the period of time just following the time when host defenses overcome microbial virulence traits?
What is the name applied to the method used by a microorganism to enter the body?
What is the single most important virulence trait of a microorganism?
Adherence to host tissues.
What is meant by the term "toxicity" as applied to microorganisms?
The symptoms of the disease are due to a toxin secreted by the organism.
What is meant by the host or tissue specificity of an infectious disease?
The organism may require a certain host or a certain tissue or both before it can produce disease.
What is the study of how a disease is transmitted?
What different routes of transmission are used by microorganisms?
Direct contact. Aerosol droplets. Fomites (inanimate objects). Ingestion. Arthropod vectors.
What allows for the specificity of the adherence of a pathogen to a host cell?
Receptors on the surface of the host cell that interact with molecules on the surface of the pathogen.
What is the name of the mechanism whereby normal flora inhibit colonization by a pathogen?
What is the name of the mechanism whereby the combined effects of two pathogens is greater than either one alone?
What is the name applied to the relative ability of a microorganism to cause disease?
What is the minimal lethal dose (MLD)?
The smallest dose of a microorganism that will result in the death of the host.
What is the lethal dose50 (LD50)?
The concentration of a microorganism that will kill 1/2 of animals infected. Survival must be used as an end point.
What is the infectious dose50 (ID50)?
The concentration of the microorganism that will infect 1/2 of animals treated. Culture of tissues from the animal for the organism is used to determine this value.
What is meant by the term "pathogenicity"?
The measure of the ability of a microorganism to cause disease.
What is the property that allows microorganisms to move into tissues and multiply in the tissues?
What part of the immune system functions to remove extracellular pathogens from the body?
Humoral immunity (antibodies).
What part of the immune system functions to remove intracellular pathogens from the body?
Cell-mediated immunity.
How do capsules help a pathogen evade host defenses?
They are anti-phagocytic.
How does the M-protein on the surface of streptococci help the organism avoid host defense?
It is anti-phagocytic.
Outline the mechanism whereby the humoral immune system functions to eliminate infections.
Activation of B cells with production of antibodies. Antibodies and complement opsonize the microorganism. Phagocytosis and intracellular killing of the organism.
What are the four steps of the phagocytic mechanism?
Chemotaxis. Opsonization. Engulfment. Intracellular killing.
How do white blood cells move to a site of infection?
Tissue damage causes endothelial cells of vessels in the area to increase expression of adhesive molecules (adhesins). WBC attach to the adhesins and move into the tissue in response to chemotactic substances.
What is the mechanism used by the cell-mediated immune response to eliminate infections?
T cell are activated and produce IFN-gamma. IFN activates macrophages to become cytotoxic and kill microorganisms. IFN activates NK cells to kill intracellular pathogens. T cell products help cytotoxic T cells develop which kill intracellular pathogens.
How do Mycobacteria avoid host defenses?
A thick waxy outer covering allows the organism to resist effects of lysosomal enzymes.
How do Salmonella avoid host defenses?
They inhibit the oxidative intermediates of phagocytes.
How does the influenza virus evade host defenses?
It inhibits fusion of lysosomes and phagosomes.
How does Listeria evade host defense?
It escapes from the phagosome into the cytoplasm.
How does Listeria infect adjacent cells?
It is coated with actin that propels the bacterium into an adjacent macrophage.
Which bacteria absolutely require an intracellular environment to grow?
Rickettsia Chlamydia
What does a virus need before it will grow?
It must be inside another cell because it is an "obligate intracellular parasite".
What part of the immune system is most effective in eliminating viral infections?
CD8+ cytotoxic T cells.
Name six diseases where the production of a toxin is of prime importance to the pathogenesis of the disease.
Botulism. Tetanus. Diphtheria. Toxic Shock Syndrome. Cholera. Scarlet Fever.
What part of the cell wall of Gram-negative bacteria is important to their pathogenesis?
Endotoxin (lipopolysaccharide, LPS).
Why is LPS toxic?
It causes macrophages to secrete proinflammatory cytokines (IL-1, TNF-alpha and IL-6). In large amounts these cause hypotension, disseminated blood clotting and lethal shock.
How do superantigens stimulate T cells and macrophages?
They bind to the TcR and to MHC outside the antigen-binding groove. This activates both cell types with the release of macrophage and T cell cytokines.
What is the morbidity rate?
The number of cases or incidence of a specific notifiable disease per unit population.
What is the mortality rate?
The number of deaths due to a specific notifiable disease per unit population.
Where is Staphylococcus aureus usually found?
In the nose of healthy individuals. Especially hospital workers.
Where is Staphylococcus epidermidis found?
It is normal flora of the skin.
Where is Staphylococcus saprophyticus found?
It is normal flora of the vagina.
What is the Gram stain characteristic and morphology of Staphylococci?
Gram-positive cocci in grape-like clusters.
What test is used to distinguish Staphylococci from streptococci?
What features distinguish Staphylococcus aureus from Staphylococcus epidermidis?
Coagulase - most important. Fermentation of mannitol. Hemolysis. Yellow pigment.
What two tests are used to distinguish different isolates of Staphylococcus aureus?
Pulsed field gel electrophoresis (PFGE). Phage typing.
What conditions supply a portal of entry for staphylococcal infections?
Skin abrasions. Insertion of needles. Catheters.
What are the virulence traits of S. aureus?
Coagulase. Protein A. Several hemolytic toxins. Enzymes - DNase, fibrinolysin, lipase, hyaluronidase. Some are encapsulated.
What staphylococcal toxins are responsible for production of food poisoning?
Enterotoxins (A-F).
How soon after eating contaminated food does staphylococcal food poisoning occur?
2-6 hrs.
Staphylococcal food poisoning is not due to the presence of a preformed toxin in food.
The correct answer is: False
What is the staphylococcal disease and toxin associated with the use of tampons?
Toxic Shock Syndrome. Toxic Shock Syndrome Toxin (TSST).
What is the mechanism where by staphylococcal toxic shock syndrome toxin (TSST) causes pathology?
The toxin induces macrophages to release large amounts of IL-1 and TNFalpha.
What staphylococcal toxin causes a condition where skin exfoliates at sites of the body other than the infection site? What is this disease called?
Exfoliative toxin. Scalded Skin Syndrome.
What three different skin infections can be caused by Staphylococcus aureus?
Furuncle - a single focus of infection. Carbuncle - Infection along facial planes with multiple heads (i.e. boils). Impetigo - a superficial skin infection.
Once spread hematogenously, where can Staphylococci form abscesses?
In most tissues.
What infection predisposes a patient to development of staphylococcal pneumonia?
What is dangerous about staphylococcal pneumonia?
It can extend into the pleural cavity causing an empyema and erode into the pericardial sac leading to pericarditis.
Is it necessary that a heart valve have previous damage for S. aureus to cause endocarditis?
What are the most common causes of staphylococcal meningitis?
Contamination of the subarachnoid space during neurosurgery. Dissemination from staphylococcal endocarditis.
Is penicillin the drug of choice for staphylococcal infection?
No. Most are resistant to this drug.
What does MRSA mean?
Methicillin-resistant Staphylococcus aureus.
Are MRSA resistant to other antibiotics?
Yes, they are resistant to a number of antibiotics. Due to a change in the penicillin-binding protein 2 (PBP-2) of the organism.
What defense mechanisms are most important for elimination of staphylococcal infections?
Innate defenses: intact skin, polymorphonuclear leukocytes.
If Staphylococcus epidermidis is cultured from the blood, what should be the criteria to make the diagnosis of staphylococcal sepsis?
The number of positive blood cultures. The presence of predisposing factors.
What medical procedures have a strong association with S. epidermidis infections?
Invasive procedures: Prosthetic heart valves, IV catheters, CSF shunts, Peritoneal dialysis.
What type of infection is caused by Staphylococcus saprophyticus infection?
Cystitis in young, sexually active females.
What is the source of Staphylococcal infection?
What are the predisposing factors that favor development of Staphylococcal infections?
Hyperactive sebaceous glands. Trauma. Indwelling catheters. Cancer. Diabetes. Cirrhosis of the liver. PMN deficiency IV drug abuse
What percentage of normal people carry Staphylococcus aureus in their nose?
What percent of hospital workers carry Staphylococcus aureus in their nose?
What are the Gram-stain and morphological characteristics of Bacillus anthracis?
Gram-positive rod. Spore formation. Encapsulated.
What three factors form two different anthrax toxins?
LF - lethal factor. PA - protective antigen. Present in both the lethal toxin and the edma toxin. EF - edema factor.
How does man become infected with anthrax?
Inhallation of spores - pulmonary anthrax. Ingestion of spores - gastrointestinal anthrax. Contaminated wound site - cutaneous anthrax.
What are the most serious consequences due to infection with the anthrax bacillus?
Pulmonary edema. Meningitis. Respiratory distress.
How do you prevent anthrax infections?
Avoid exposure. Vaccination. Proper destruction of contaminated animals.
What type of disease is caused by Bacillus cereus?
What is responsible for the symptoms of B. cereus food poisoning?
A heal-labile toxin. This is an intoxication.
What food is commonly associated with B. cereus food-poisoning?
Fried rice.
What organism causes diphtheria?
Corynebacterium diphtheriae
What are the gram-stain and morphological features of C. diphtheriae?
Gram-positive rod. Club shaped, arranged in palisades.
What distinguished Corynebacteria from Listeria?
Listeria are motile at room temperature.
What is the most important virulence trait of C. diphtheriae?
Diphtheria toxin.
In what species is C. diphtheriae found?
Only in man.
How do you treat patients with diphtheria?
Antitoxin. Antibiotics.
How can you prevent diphtheria infections?
Vaccination against the diphtheria toxin (part of the DPT childhood vaccine).
What are the gram-stain and morphological characteristics of Listeria monocytogenes?
Gram-positive. Small bacilli (coccobacilli) in palisades.
How does Listeria monocytogenes escape host defenses?
By growing in an intracellular location.
What type of immunity is most effective in eliminating Listeria infection?
Cell mediated immunity.
What are the virulence factors of L. monocytogenes?
Listeriolysin-O - helps bacterium escape from the phagosome. Phospholipase-C - helps escape into adjacent cells. Internalins - mediate binding and entry into host cells.
In what human populations is Listeria infection of the most concern?
Neonates. Immunocompromised.
How are Listeria infections acquired?
At birth during passage through the vaginal tract. Transplacentally. From Contaminated food (deli meats, cheese, hot dogs etc.).
How do you avoid Listeria infections?
Avoid animal carcases. Eat pasteurized dairy products.
What are the Gram stain characteristic and morphology of the Streptococci?
Gram-positive cocci in chains.
What laboratory test distinguishes Streptococci from Staphylococci?
Catalase test.
What are the three hemolytic classes of the Streptococci?
Alpha - green. Beta - clear. Gamma - no hemolysis.
What type of hemolysis does Streptococcus pyogenes have?
Beta hemolytic.
What is the natural habitat of Streptococcus pyogenes?
The pharynx and skin.
What is the most important virulence trait of Streptococcus pyogenes?
M protein - anti-phagocytic.
Name four activities of the streptococcal erythrogenic toxins.
Causes erythematous rash. Pyrogenic (fever producing). Mitogen (causes cells to proliferate). Superantigen (stimulates T cells and macrophages to release cytokines that mediate shock).
How does Streptococcus pyogenes obtain the genes for erythrogenic toxin production?
By bacteriophage infection.
Which erythrogenic toxin of Streptococcus pyogenes is responsible for scarlet fever?
Erythrogenic toxin A - speA
What are the activities of Streptolysin O?
Membrane damaging - beta hemolysis Cardiotoxic
What serological test indicates a recent infection with Streptococcus pyogenes?
Anti-streptolysin O (ASO).
Name two factors that are responsible for spreading of Streptococcus pyogenes?
Hyaluronidase. Streptokinase.
Name three noninvasive diseases caused by Streptococcus pyogenes.
Strep throat. Cellulitis. Impetigo.
Name four invasive diseases caused by Streptococcus pyogenes.
Necrotizing fasciitis. Streptococcal toxic shock syndrome. Bacteremia. Pneumonia.
Name two nonsuppurative sequelae of infection with Streptococcus pyogenes.
Rheumatic fever. Post-streptococcal glomerulonephritis.
How is Streptococcus pyogenes transmitted?
Person to person - contact with infected secretions.
Who is at risk of developing invasive streptococcal infection?
The elderly. Immunosuppressed. Chronic diseases. African-American. American Indian.
Who is at risk of noninvasive disease caused by Streptococcus pyogenes?
Elementary age school children.
What are the clinical findings in patients with strep throat?
Red and edematous posterior pharynx with white exudate on the tonsils.
How do you diagnose strep throat in the laboratory?
Throat culture or rapid test for Group A carbohydrate.
What are the clinical findings in patients with scarlet fever?
Erythematous rash on the skin concurrent with a streptococcal infection.
What infection results from infection of skin and subcutaneous tissues with Streptococcus pyogenes?
What infection occurs when Streptococcus pyogenes infects skin forming crusty lesions?
What infection with Streptococcus pyogenes causes deep seeded infection of subcutaneous tissues with loss of skin?
Necrotizing fasciitis.
Streptococcus pyogenes infection can not cause toxic shock syndrome.
The correct answer is: False
What laboratory tests are used to identify Streptococcus pyogenes?
Catalase negative. Beta hemolytic. Sensitive to bacitracin.
Streptococcus pyogenes is known to develop resistance to penicillin.
The correct answer is: False
Which Streptococcal species is in Lancefield group B and is a normal inhibitant of the vagina, intestinal tract and pharynx?
Streptococcus agalactiae.
Name three types of infections caused by Streptococcus agalactiae following obstetrical procedures.
Puerperal sepsis. Intra-amniotic infection. Septic abortion.
Name three types of infection caused by Streptococcus agalactiae that are not associated with obstetrical procedures.
Urinary tract infections. Wound infections. Endocarditis.
What diseases in the infant are associated with Group B streptococcal infection?
Still birth. Prematurity. Septicemia. Meningitis.
How are babies infected with Group B streptococci in utero?
Aspiration into the lungs from an infected mother.
How can Group B infections of infants be avoided?
Treatment of mothers with intrapartum antibiotic prophylaxis.
To what Lancefield group do Enterococcus faecalis and Enterococcus faecium belong?
Group D
What is the normal habitat of the enterococci?
They are normal intestinal flora.
What types of infections are caused by the enterococci?
Endocarditis. Urinary tract infections. Septicemia. Nosocomial (hospital acquired) infections.
What underlying conditions predispose to development of infections with enterococci?
Advanced age. Chronic diseases. Invasive procedures. Previous colonization with multidrug-resistant organisms.
What is the leading pathogen with resistance to antimicrobial drugs?
Enterococcus faecalis.
What type of hemolysis do members of the oral streptococci exhibit?
Alpha. Gamma.
Name four species of Streptococci found in the oral cavity.
Streptococcus mitis. Streptococcus salivarius. Streptococcus sanguis. Streptococcus mutans.
What three factors contribute to the development of dental caries?
Teeth susceptible to acid demineralization. Sugars in the diet. Streptococcus mutans.
What is the "window of infectivity" with Streptococcus mutans?
12-24 months after the emergence of the first tooth.
When does Streptococcus mutans disappear from the mouth?
When all the teeth are lost.
What is the best way to prevent caries?
Reduce sucrose in the diet. Flouridation of water.
What is the leading cause of bacterial endocarditis?
Oral streptococcus showered into the circulation during dental procedures.
Who is at risk of developing endocarditis following dental procedures?
Patients who have had rheumatic heart disease or congenital heart defects.
What are the Gram stain characteristic and morphology of Streptococcus pneumoniae?
Gram-positive lancet shaped cocci in pairs.
What is the normal habitat of Streptococcus pneumoniae?
The pharynx.
What types of infections are caused by Streptococcus pneumoniae?
Pneumonia. Meningitis. Otitis media.
What is the major virulence factor of Streptococcus pneumoniae?
Capsule - anti-phagocytic.
What laboratory tests are used to identify Streptococcus pneumoniae?
Catalase negative. Alpha hemolytic. Sensitive to optochin.
What populations are at risk of developing infection with Streptococcus pneumoniae?
Elderly. Children under 2 years old. American Indians. Alaskan Natives. Children in day care. HIV+. Sickle-cell disease.
Streptococcus pneumoniae is known to have antibiotic resistance.
The correct answer is: True
What is the best way to prevent infections with Streptococcus pneumoniae?
Vaccination - a capsular polysaccharide vaccine containing 23 different capsular types is available.