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23 Cards in this Set
- Front
- Back
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Name the diseases caused by E. coli?
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E. coli can cause diarrhea(bloody and non) UTI, neonatal meningitis, nosocomial pneumonia.
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Where does E. coli normally colonize and how is it transmitted?
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E. coli is considered normal flora of the colon that is transmitted fecally-orally.
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How is E. coli infection diagnosed?
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Lab culture, E. coli is Gram neg, lactose fermenting and Beta hemolytic(not all strains)
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E. coli is classically associated with what three antigens?
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O antigen(somatic antigen)
K antigen(capsular '''' H antigen(flagellar antigen) O and H are used for serology |
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What larger structure is the O antigen a part of?
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O antigen is part of LPS endotoxin.
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What does the lack of H antigen signify?
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H antigen is part of the flagellae. Strains without it lack flagellae and are nonmotile.
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Why would E. coli with the K1 antigen be troubling to physicians?
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K1 strains cause neonatal meningitis, bacteremia and UTI.
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What are the 5 strains of virulent enteric E coli?
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Enterotoxigenic E. coli (ETEC)
enterohemorrhagic E. coli(EHEC) enteroinvasive E. coli(EIEC) enteropathogenic E.coli(EPEC) enteroaggregative E.coli(EAEC) |
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What two toxins does ETEC travelers diarrhea produce?
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Heat labile toxin(LT) and heat stable toxin(ST)
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What is the mechanism of heat LT?
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It activates Gs via ADP ribosylation leading to constant activation ofadenylate cyclase and high levels of cyclic adenosine monophosphate(cAMP). This causes increased secretion of Cl- ions from intestinal cells into the GI lumen. negative Cl- ions cause positive charged Na+ ions to follow. Water follows Na+ into the lumen leading to diarrhea.
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What is the mechanism of action for ST?
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It activates guanylate cyclase leading to increased cGMP and ultimately decreased water absorption from the GI lumen.
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Which other bacterial toxin is similar to LT toxin?
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Cholera toxin.
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What toxin mediates EHEC diarrhea?
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Shiga like toxin(verocytotoxin) inhibits 28S component of the 60S ribosome subunit, inhibiting protein synthesisi leading to cell necrosis.
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How do patients with EHEC present?
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Afebrile and bloody diarrhea without inflammatory white blood cells. EHEC strain 0157:H7 is associated with hemolytic-uremic syndrome(HUS).
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What is the mechanism that causes HUS?
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HUS occurs when Shiga like toxin(verocytotoxin) enters the blood stream. Cardinal features are thrombocytopaenia, anemia and acutre renal failure.
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How are patients typically exposed to EHEC 0157:H7?
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Undercooked hamburger, meat and direct contact with animals(after children have been to a petting zoo)
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How is EHEC treated?
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Fluids and supportive therapy. Antibiotics are not useful and may predispose to HUS.
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The main virulence factors of EIEC are encoded by a plasmid shared by what other diarrhea causing bacteria?
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Shigella.
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How do these plasmid encoded proteins act?
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These plasmid encoded proteins allow for adherence and direct invasion of epithelial cells in the gut.
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How do patients with EIEC present?
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Fever and bloody diarrhea with inflammatory WBC.
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EPEC adheres to but does not invade intestinal cells and results in flattening of the intestinal villi.What is the consequence of this and how does it present?
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This leads to malabsorption. Patients present with fever and bloody diarrhea.
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Who does EPEC commonly affect?
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Children, associated with nursery breakouts.
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E. coli is the most common cause of UTIs, what is the key virulence factor?
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P-pili that mediate adhesion to urinary epithelium.
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