E Coli Flashcards
What is the difference between commensal and enteropathogenic E Coli?
Commensal: part of normal gut flora. Enteropathogenic: has evolved to be a GI pathogen by acquiring virulence genes.
What is the major serotype of EHEC?
O157:H7
Sources of EHEC infection?
undercooked food, contaminated food, unpasteurized juice/milk. also, person to person contact
what is the infectious dose for EHEC?
very low (<100 bugs)
Commensal E Coli synthesizes what?
Vitamin K
what is HUS? what bacterium is it associated with?
Hemolytic uremic syndrome. Destruction of RBCs and damage to lining of blood vessel walls. associated with EHEC.
Clinical profile of EHEC infection? will be become systemic?
abd pain, bloody diarrhea. if severe, acute renal failure. cells remain extracellular (does not become systemic/no bacteremia)
what proteins are unique to EHEC? what do they do?
Tir and intimin. Tir: T3SS-secreted, delivered to surface of epithelial cells through T3SS needle to allow E Coli attachment. Intimin: Tir binding protein on surface of E Coli.
With EHEC, what does the T3SS do? where are the genes coded?
induces formation of attaching/effacing lesions. encoded on pathogenicity island called LEE (locus for enterocyte effacement)
what bacteria has shiga toxin? which has shiga-like toxin?
Shiga: shigella. Shiga-like: EHEC.
What is EHEC aka?
STEC (shigalike toxin E coli)
what does the EHEC shiga-like toxin do?
disrupts eukaryotic protein synthesis and is cytotoxic. interferes with protein synthesis via RNA cleavage activity (subunit A) and may impact cytoskeleton (Subunit B)
HUS is attributed to the activity of what?
shiga-like toxin
Discuss hemolysin
pore-forming protein that inserts into host cell membranes. common in E coli strains that cause meningitis. present in other gram-neg pathogens. encoded by a plasmid.
What is the leading cause of diarrhea in children in dev countries?
EPEC
How is EPEC transmitted?
person to person
EPEC: clinical profile
A/E lesions. diarrhea.
EPEC: toxins detected in stool?
no
What is the cause of traveler’s diarrhea?
ETEC
The type of E Coli that will adhere to enterocytes in the small intestine?
ETEC
how does ETEC adhere to enterocytes of the small intestine?
to specific receptors on enterocytes, via fimbriae
what toxins are associated with ETEC?
Heat-labile toxin (LT) and heat-stabile toxin (ST).
Describe heat-labile toxin
similar to cholera toxin. binds host cell receptor, targets adenylate cyclase, leading to increased cAMP levels. results in excess chloride ion secretion and blocked sodium ion uptake. net loss of fluid and electrolytes –> watery diarrhea.
describe heat-stabile toxin
alters cGMP levels –> watery diarrhea via same pathway as heat-labile toxin.
childhood diarrhea in dev countries similar to EPEC?
EAEC
which is more aggressive: EPEC or EAEC?
EAEC due to more aggressive epithelial cell attachment.
what toxins are produced by EAEC?
a heat stabile-like toxin (called EAST: enteroaggregative stable toxin), a plasmid-encoded toxin, and hemolysin
2 forms of E Coli that form A/E lesions?
EAEC and EPEC
Which form of E Coli attaches to cells via non-fimbrial adhesins?
EIEC
What cells does EIEC invade? does it become systemic?
invades mucosal cells and multiplies within them. does not become systemic.
which E Coli strain produces watery diarrhea that contain blood and mucus? what other enteric causes this?
EIEC. other: shigella
what E Coli strain has genes for invasion, replication and survival that are very similar to shigella?
EIEC. these genes are encoded on a plasmid.
Do EIEC strains produce ST and LT?
no
what led to a deadly E Coli outbreak in germany in 2012?
Combination of ability to form aggregates on cells (like EAEC) and to produce shiga-like toxin (as in EHEC/STEC). produce of continual evolution of E Coli strains.
Can E Coli ferment lactose? Can shigella, salmonella?
Yes. No, No
Main diagnostic tool for determining if O157:H7 or commensal E Coli?
Sorbitol. O157:H7 cannot grow on sorbitol, commensal E Coli can grow on sorbitol.
O-antigens are only present in what kind of bacteria?
Gram-neg
How did the various forms strains of E Coli become different from one another?
Different virulence factors were taken up by horizontal transfer and resulted in different strains.
What is the enterohemorrhagic strain of E Coli? Which are diarrheagenic?
EHEC. Diarrheagenic: EPEC, EIEC, ETEC, EAEC.
The LEE locus codes for what essential component of E Coli?
The T3SS system. Allows bacterium to deliver proteins to the host cell.
What do genes esp A, B and D do?
All are part of the LEE locus: A codes for the filament of the T3SS needle, and B and D pass through the needle to the host cell cytoplasm to form PORES.
How did E Coli acquire shiga-like toxin?
Via bacteriophage.
Does EPEC have tir and intimin?
Yes.
What is the difference between the pili in EPEC and the pili in EHEC?
in EPEC, the pili form bundles: bundle-forming pili (BFP). helps with adherence to host cells.
EHEC has which toxin?
Shiga-like toxin.
ETEC has which toxin?
ST, HT (heat stable toxin, heat labile toxin)
EAEC has which toxin?
EAST: EnteroAggregative stable toxin
EIEC has which toxin?
none. Does not possess Shiga toxin or other known E. coli toxins.
How can we tell commensal E Coli from virulent E Coli strains?
Commensal: ferments sorbitol. Virulent: does NOT ferment sorbitol.
