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23 Cards in this Set

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Name the diseases caused by E. coli?
E. coli can cause diarrhea(bloody and non) UTI, neonatal meningitis, nosocomial pneumonia.
Where does E. coli normally colonize and how is it transmitted?
E. coli is considered normal flora of the colon that is transmitted fecally-orally.
How is E. coli infection diagnosed?
Lab culture, E. coli is Gram neg, lactose fermenting and Beta hemolytic(not all strains)
E. coli is classically associated with what three antigens?
O antigen(somatic antigen)
K antigen(capsular ''''
H antigen(flagellar antigen)

O and H are used for serology
What larger structure is the O antigen a part of?
O antigen is part of LPS endotoxin.
What does the lack of H antigen signify?
H antigen is part of the flagellae. Strains without it lack flagellae and are nonmotile.
Why would E. coli with the K1 antigen be troubling to physicians?
K1 strains cause neonatal meningitis, bacteremia and UTI.
What are the 5 strains of virulent enteric E coli?
Enterotoxigenic E. coli (ETEC)
enterohemorrhagic E. coli(EHEC)
enteroinvasive E. coli(EIEC)
enteropathogenic E.coli(EPEC)
enteroaggregative E.coli(EAEC)
What two toxins does ETEC travelers diarrhea produce?
Heat labile toxin(LT) and heat stable toxin(ST)
What is the mechanism of heat LT?
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.
What is the mechanism of action for ST?
It activates guanylate cyclase leading to increased cGMP and ultimately decreased water absorption from the GI lumen.
Which other bacterial toxin is similar to LT toxin?
Cholera toxin.
What toxin mediates EHEC diarrhea?
Shiga like toxin(verocytotoxin) inhibits 28S component of the 60S ribosome subunit, inhibiting protein synthesisi leading to cell necrosis.
How do patients with EHEC present?
Afebrile and bloody diarrhea without inflammatory white blood cells. EHEC strain 0157:H7 is associated with hemolytic-uremic syndrome(HUS).
What is the mechanism that causes HUS?
HUS occurs when Shiga like toxin(verocytotoxin) enters the blood stream. Cardinal features are thrombocytopaenia, anemia and acutre renal failure.
How are patients typically exposed to EHEC 0157:H7?
Undercooked hamburger, meat and direct contact with animals(after children have been to a petting zoo)
How is EHEC treated?
Fluids and supportive therapy. Antibiotics are not useful and may predispose to HUS.
The main virulence factors of EIEC are encoded by a plasmid shared by what other diarrhea causing bacteria?
Shigella.
How do these plasmid encoded proteins act?
These plasmid encoded proteins allow for adherence and direct invasion of epithelial cells in the gut.
How do patients with EIEC present?
Fever and bloody diarrhea with inflammatory WBC.
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?
This leads to malabsorption. Patients present with fever and bloody diarrhea.
Who does EPEC commonly affect?
Children, associated with nursery breakouts.
E. coli is the most common cause of UTIs, what is the key virulence factor?
P-pili that mediate adhesion to urinary epithelium.