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78 Cards in this Set

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What are the 3 staphylococcus species?
S.aureus
S.epidermitis
S.saprophyticus
What clinical diseases are caused by S.aureus?
scalded skin syndrome
food poisoning
toxic shock syndrome
cutaneous infections
bacteremia
endocarditis
osteomylitis
septic arthritis
General characteristics of Staphylococcus spp.
Gram-positive cocci
grow in grape-like clusters
What environment does S.aureus grow in?
facultative anaerobe - can grow in both aerobic and anaerobic environments
How does S.aureus protect itself from phagocytosis?
polymorphonuclear leukocytes (PMNs) located on its capsule
How does S.aureus protect itself from an immune response?
Protein A binds the Fc receptor on the immunoglobulin, blocking immunoglobulin from binding to antigen
What is the role of teichoic acid in the pathogenicity of S.aureus
mediate binding to fibronectin
What is the role of peptidoglycan in the pathogenicity of S.aureus
endotoxin-like activity
peptidoglycan binds to TLR2 to activate inflammatory host response
overstimulation of the immune system can lead to septic shock
What mechanism accounts for S.aureus being coagulase positive?
Coagulase enzyme converts fibrinogen on cell surfaces to insoluble fibrin, causing S.aureus to clump
What toxin in S.aureus is responsible for forming a pore in host cells eventually causing lysis of the host cell?
alpha hemolysin
forms a 1-2nm pore causing efflux of K+ and influx of Na+ and Ca2+
this changes the osmotic gradient, resulting in the cell being hypertonic to the environment
water enters the cell, leading to osmotic swelling and eventual lysis of the cell
Desquamation of skin tissue due to action of exfoliating toxins is characteristic of what clinical disease?
scalded skin syndrome due to S.aureus infection
What are the characteristics of staphylococcal food poisoning?
caused by S.aureus
due to action of enterotoxins A-E and G-I
produced by 30-50% of S.aureus strains
acts directly on neural receptors to stimulate vomiting 2-5 hrs after ingestion
resistant to boiling for 30 minutes and digestive enzymes
usually self-limiting
What causes toxic shock syndrome?
S.aureus colonizes vagina and produces the toxin TSST-1
What are the symptoms of toxic shock syndrome?
high fever
vomiting
diarrhea
sore throat
muscle pain
rash
hypotension
organ failure
What is the mechanism of pathogenicity of TSST-1?
TSST-1 is a superantigen that promotes the release of cytokines
at low concentration, TSST-1 causes leakage of endothelial cells
at high concentration, TSST-1 causes cell death
TSST-1 can cross mucous membranes to exit site of initial infection and cause systemic disease
What cutaneous infections are caused by S.aureus?
furuncles (boils) - blockage of hair follicle or sweat gland that eventually becomes infected
carbuncle - spread of furuncle infection causing abscesses on adjacent tissues
impetigo - small macule enlarges, fills with pus, then ruptures
folliculitis - hair follicle is reddened and raised with pus, known as a stye if it occurs on the eyelid
How is S.aureus diagnosed?
Gram stain - gram positive cocci in clusters
Culture on blood agar plates - colonies are gold in color with a zone of hemolysis
catalase test - catalase positive
coagulase test - coagulase positive
What is MRSA and how would you treat it?
methicillin resistant staph aureus

resistance occurs due to acquisition of a new gene mecA that encodes for a new PBP called PBP2'

treat with vancomycin
What is the leading cause of nosocomial infections?
Staphylococcus spp.
Staph epidermidus causes 50% of all catheter and shunt infections
What are general characteristics of S.saprophyticus?
Gram-positive cocci in urine
causes urinary tract infections in young sexually active women

symptoms include pain on urination and pus in urine

usually successfully treated with antibiotics
What are general characteristics of Streptococcus?
Gram-positive cocci arranged in chains or pairs
Catalase negative
What are general characteristics of S.pyogenes?
beta-hemolytic streptococcus in Lancefield group A
causes purulent infections
What is M protein and what bacteria is it associated with?
cell surface exposed protein composed of 2 alpha helices
functions as an adhesin and antiphagocytic protein in S.pyogenes
What are two pore-forming toxins associated with S.pyogenes and what are their pathogenic effects?
Streptolysin O - forms pores in human cell plasma membrane, lyses erythrocytes and is responsible for beta hemolysis

Streptolysin S - forms pores in plasma membranes of human cells and erythrocytes, serum antibody production against SLS used to diagnose recent Streptococcal infection
What enzymes promote spreading of S.pyogenes bacteria in infected tissues?
Streptokinase A and B - cleave plasminogen setting off a signal cascade resulting in lysis of fibrin clots

DNase A and D - break down DNA present in pus causing reduction in viscosity in abscesses
What is the mechanism of C5a peptidase's pathogenicity?
C5a peptidase cleaves C5a of the complement system

C5a is responsible for recruiting neutrophils and macrophages to the site of infection

Thus, C5a peptidase prevents recruitment of immune system cells in S.pyogenes infection
What clinical diseases are caused by S.pyogenes infection?
pharyngitis (strep throat)
scarlett fever
skin infections
necrotizing fasciitis
streptococcal toxic shock syndrome
bacteremia
What causes scarlett fever?
Strains of S.pyogenes that produce streptococcal pyrogenic exotoxins (SpeA, SpeB, SpeC, SpeD)

toxins act as superantigens, leading to release of cytokines and resulting in inflammation
What skin infections are associated with S.pyogenes?
impetigo
cellulitis
How is S.pyogenes diagnosed?
Gram stain - Gram positive cocci in chains
Blood Agar culture - causes beta-hemolysis and is catalase negative
rapid strep test to diagnose pharyngitis
How is S.pyogenes treated?
Penicillin
Erythromycin if Penicillin allergy exists
treat severe infections with Penicillin + Clindamycin
What are the general characteristics of Streptococcus agalactiae?
Gram positive cocci in chains
beta-hemolytic
Group B
causes neonatal sepsis and meningitis
can colonize the vagina and be passed to infant through delivery
What are some important species of Viridans Streptococci?
S.bovis - correlated with colon malignancies
S.pneumoniae - leading cause of community-acquired pneumonia
What are some general characteristics of the Enterococci spp?
normally inhabit GI tract
second most common cause of nosocomial infections
gamma-hemolytic
What are the medically important species of Enterococci?
E.faecalis
E.faecium
What clinical diseases are caused by Enterococci infection?
surgical wound infection
urinary tract infection
biliary tract infection
intraabdominal infections
bacteremia
How are Enterococci infections treated
Penicillin or Ampicillin - resistance is a problem

Vancomycin
What are general characteristics of Bacillus Anthracis?
Gram positive rods in chains
spore forming
aerobic
What diseases are caused by Bacillus Anthracis?
Cutaneous Anthrax
Inhalation Anthrax
Gastrointestinal Anthrax
What are the symptoms of cutaneous anthrax?
spores are introduced into the skin
small red macule forms
macule enlarges to form an ulcer
usually resolves spontaneously
20% mortality rate
What are the symptoms of inhalation anthrax?
spores are inhaled
symptoms similar to severe respiratory infection:
fever
shortness of breath
hypotension
shock
death within 3 days
What are the symptoms of gastrointestinal anthrax?
ingested from contaminated meat
mortality rate approaches 100%
Describe the structure of the anthrax toxin.
A-B subunit toxin

A = activity
Edema factor (EF) - adenylate cyclase activity causes inflammation and inhibits neutrophil activity
Lethal factor (LF) - zinc metalloprotease that cleaves host cell kinases and causes lysis or inactivation of macrophages, dendritic cells, and suppressor T cells

B = binding
Protective antigen (PA) binds to cells and facilitates entry of EF and LF
How is bacillus anthracis diagnosed?
Gram stain - gram negative in chains
Growth on blood agar plates streaked with pus or sputum
serologic tests
What are general characteristics of Listeria monocytogenes?
Gram positive bacillus
Metabolically facultative - grows in aerobic and anaerobic conditions
foodbourne transmission
beta-hemolytic
catalase positive
What clinical diseases are caused by Listeria monocytogenes?
meningitis
fetal infections
neonatal infections
What virulence factors enable Listeria monocytogenes to travel from cell to cell without entering the extracellular environment?
internalin
listeriolysin O
phospholipases C enzymes
ActA - polymerization of actin into a comet tail that allows bacteria to invade neighboring cell
Why is a Gram stain not used to diagnose Listeria monocytogenes?
Listeria monocytogenes is present in too low a number to be detected via Gram stain of the CSF
How is Listeria monocytogenes diagnosed?
Growth of organism on blood agar plate from CSF, blood, or amniotic fluid
Small smooth colonies surrounded by rim of beta-hemolysis
catalase positive
How is Listeria monocytogenes treated?
Ampicillin
What are the general characteristics of Corynebacterium?
aerobic Gram positive bacilli
irregular swelling on one end causes club-shape
non-spore forming
What are the medically important species of Corynebacterium?
C.diphtheriae
C.ulcerans
C.jeikeium
Describe the clinical disease caused by C.diphtheriae.
Diphtheria
spread by person-to-person direct contact or droplets
symptoms include sore throat, fever, difficulty swallowing, cough, hoarseness, rhinorrhea
Pseudomembrane composed of necrotic cell debris, fibrin, and blood cells form on oropharynx, palate, nasopharynx, nose, or larynx
What toxin is associated with C.diphtheriae?
Diphtheria toxin (DT)
heat labile
gene carried on phage
A-B toxin
A inhibits peptide elongation by ADP-ribosylating EF-2
inhibition of protein synthesis in pharyngeal epithelium --> necrosis
What toxin are ADP-ribosylating toxins and what is its mechanism of action?
transfer ADP-ribose from NAD to host cell proteins, causing altered activity of host cell proteins

ADP-ribosylating toxins:
exotoxin A of P.aeruginosa
cholera toxin of Vibrio cholerae
heat labile toxin of E.coli
Pertussis toxin of Bordetella pertussis
What are the treatments for Corynebacterium diphtheriae?
horse antisera against dyphtheria toxin
antibiotics - do not increase rate of healing, but do prevent spread of organism
close monitoring for respiratory or cardiac failure
What is a toxoid?
chemically treated toxin that is no longer toxic but retains immunogenicity

useful as a vaccine
What are the general characteristics of the Clostridia spp. of bacteria?
gram positive rods
spore-forming
strictly anaerobic
What are the medically important species of Clostridia?
C.tetani
C.botulinum
C.perfringens
C.difficile
What bacteria causes tetanus?
Clostridium tetani
What are the mechanisms of pathogenicity of C.tetani?
Tetanus toxin (tetanospasmin)
A-B toxin
A chain consists of a protease that cleaves proteins in neuronal synapses, resulting in blockage of neurotransmitter release
B chain mediates binding of cell receptors of inhibitory motor neurons in spinal cord
How does Tetanus toxin cause Tetanus?
toxin released from C.tetani binds to peripheral motor neuron terminals

peripheral motor neurons --> axons --> neuron cell bodies in CNS

in neuron cell bodies, Tetanus toxin blocks release of presynaptic inhibitory neurotransmitters

reduction in inhibition causes increased resting firing rate of motor neurons
What are the symptoms of Tetanus?
increased masseter muscle tone (lockjaw)
increased tone of neck, shoulder, and back muscles
increased tone of abdominal and leg muscles
spasms
sympathetic nervous system symptoms: hypertension, tachycardia, arrhythmia, sweating, vasoconstriction
neonatal tetanus
What are treatment and prevention techniques of C.tetani infections?
Treatment: penicillin, tetanus immunoglobulin

Prevention: tetanus toxoid vaccine
What is the mechanism of pathogenicity of C.botulinum?
Botulinum toxin
A-B toxin
A subunit - protease that cleaves components of neuroexocytosis apparatus, blocking release of ACh
B subunit - mediates binding to cell receptors of neurons in neuromuscular junction

net result is decreased motor neuron activity due to blocked transmission of nerve impulses

botulinum toxin variants encoded by genes carried on bacteriophages
What are the clinical diseases caused by C.botulinum?
Food-borne botulism - ingestion of toxin leads to symmetric descending paralysis, cranial nerve involvement (diplopia, dysarthria, dysphagia, resp. failure), nausea, vomiting, abdominal pain

Wound botulism - wound contamination with C.botulinum spores causes symptoms similar to food-borne botulism but without the GI findings

Infant botulism - C.botulinum colonizes the infant intestine causing paralysis; can be prevented by avoiding honey for infants less than 12 months of age
What is the treatment for C.botulinum infection?
respiratory support
trivalent equine antitoxin
What clinical illnesses are caused by C.perfringens?
food-poisoning
gangrene
What clinical diseases are caused by C.difficile?
diarrhea associated with antibiotic use
What are general characteristics of Actinomycetes?
G+ rods
resemble fungi
2 medically important genera:
Actinomyces spp.
Nocardia spp.
What are the general characteristics of Nocardia spp.
Belong to the Actinomycetes family
G+ bacilli in elongated chains or filaments with branches
aerobic
2 medically important species:
N.asteroides
N.brasilliensis
What are the mechanisms of Nocardia's pathogenicity?
neutralize oxidants
prevent phagosome acidification
inhibit phagosome-lysosome fusion
lesions infiltrated with neutrophils but neutrophils are unable to kill the bacteria
What clinical diseases are caused by Nocardia infection?
Pulmonary nocardiosis - subacute pneumonia with nodules, cavitation, and empyema; dissemination to CNS, skin, soft tissue, and other organs can lead to abscess formation

Transcutaneous inoculation (actinomycetoma) - caused by inoculation of organism into tissues of the foot, fistula formation, serous or purulent discharge, lesions
How are Nocardia infections treated?
Trimethoprim/sulfamethoxazole and other sulfa drugs
Minocycline and amikacin are alternatives
treatment must be continued for 6-12 months to prevent relapse
drainage of brain abscesses
What are general characteristics of Actinomyces spp.?
part of the Actinomycetes family
G+ bacilli
facultative anaerobes, but grow best anaerobically
non-spore forming
found in normal flora of mouth, GI tract, and female genital tract
What clinical diseases are caused by Actinomyces infection?
Actinomycosis
oral-cervicofacial disease
abdominal or pelvic disease
What is a diagnostic feature of Actinomyces in Gram staining?
sulfur granules
How is Actinomyces infection treated?
Penicillin for up to 12 months

Tetracycline/doxycycline is an alternative