E coli Flashcards
If you were to grow a member of Escherichia coli on MacConkey agar, what would you expect to see?
Most members of Escherichia coli are lactose fermenters. Lactose fermentation on MacConkey agar causes a bright pink color to develop on the normally yellowish medium. A precipitate may be present.
What is a potential complication of E. coli?
HUS - hemolytic uremic syndrome. Complicates about 5-10% of E coli infections
What is the treatment for uncomplicated E coli infection? What is the treatment for severe disease? What is a contraindication for this treatment?
Most E coli disease is mild and self-limiting. Supportive therapy only.
For severe disease, consider TMP-SX or FQ (cipro) BUT this is contraindicated if there is any possibility that the pathogen is enterohemorrhagic E coli! Addition of antibiotics can cause development of HUS.
What type of pili are associated with non-pathogenic strains of E coli?
Type 1.
When opportunistic (not true pathogenic) E coli travel to other sites, what virulence factors are generally responsible for the inflammation that occurs?
LPS
a-hemolysin
Which groups of E coli can be transmitted via fomites?
Those with especially low infectious doses:
EPEC (fomite transmission to kids, primarily)
EHEC
Describe the mechanism of ETEC’s toxins
(Associated with enterotoxigenic E coli)
Heat labile toxin (LT) causes accumulation of cAMP.
Heat stable toxin (ST) causes accumulation of cGMP.
Describe the mechanism of ETEC’s ST toxin
The heat-stable ETEC toxin is a small peptide that causes the accumulation of cGMP. This causes hypersecretion of electrolytes and fluids in to the lumen of the intestine, and contributes to an osmotic imbalance leading to secretory diarrhea.
What virulence factors are associated with the disease commonly referred to as “Traveler’s Diarrhea”?
LT (heat labile)
ST (heat stable)
Which group within E coli are NOT lactose fermenters?
Enteroinvasive E coli. These are very similar to Shigella spp!
What type of pili are found on EIEC?
None!
Which E coli is NOT motile?
Enteroinvasive E coli
Enteroinvasive E coli typically affect what demographic?
Children < 5 YO in resource-limited countries.
A young patient presents with watery diarrhea that progresses to dysentery. Pus is present in stools. What is the most likely pathogen, and what could be used to diagnose (if necessary)?
Enteroinvasive E coli causes dysentery with pus in stools.
Dx can be confirmed with tissue culture or DNA probe. This is the only group within E coli that does NOT ferment lactose, has no pili, and is non-motile.
What is one difference in transmission between Shigella and EIEC?
What are some similarities?
Shigella has a very low infectious dose
EIEC has a very high infectious dose
These can be difficult to differentiate: neither ferment lactose, both a non-motile, neither produce H2S, both present with fever and watery diarrhea that progresses to dysentery with pus in stools.
What types of E coli present with diarrhea with mucous?
Enteropathogenic E coli
Enteroaggregative E coli
What types of E coli are most likely to cause protracted diarrheal illness?
Enteropathogenic
Enteroaggregative
Which types of E coli are associated with Stx?
Enterohemoragic E coli
Enteroaggregative E coli, sometimes
Describe the main virulence factor used by enteropathogenic E coli
Attaching and effacing
This is actually amazing, watch it: https://youtu.be/gnNFNI9_pT0
- Sticky pili help “land” bacteria on enterocyte
- Type III injection system injects Esps and other proteins into host (like a syringe into the host membrane)
- Intimins are injected into host cell.
- These pop through the host membrane and create landing space for the bacteria to tightly attach to the host
- Cytoskeletal proteins are recruited; actin monomers polymerize to force the creation of a “throne” for the EPEC
What is the only E coli group we learned about with an animal reservoir? What is that reservoir?
Enterohemorrhagic E coli can be found in the gut of cattle (NOT the muscle). This is why ground meat has a higher risk of being contaminated than a steak, for example.
Describe the virulence factors associated with enterohemorrhagic E coli.
Attaching and effacing occurs
The PRIMARY virulence factor = Stx, shiga toxin/serotype O157:H7.
Shiga toxin is released by the bacteria and is taken up by the enterocyte. The toxin alters the aminoacyl-tRNA entry site, shutting down proteins synthesis.
The toxin can be disseminated, potentially causing thrombocytopenia, renal failure, and/or HUS.
Buzzword: ground meat
Enterohemorrhagic E coli
Of the E coli groups we learned about, which one is primarily found in adults in industrialized countries?
Enterohemorrhagic E coli
What medium is used to culture EHEC? Why, and what are the results?
Modified Sorbitol MacConkey (SMAC) agar is used to isolate serotype O157:H7.
This agar has no lactose, but does contain sorbitol.
Other E coli organisms produce B-glucuronidase to ferment sorbitol/MUG, producing pink colonies and/or fluorescing under UB light.
EHEC does NOT produce B-glucuronidase to ferment sorbitol/MUG. Their colonies are colorless/do not fluoresce under UV light.
Colorless colonies should be serotyped for confirmation by adding antiserum: if it clumps with the addition of O157:H7 antisera, it is EHEC.
A titer is drawn from a patient suspected to have been previously intoxicated by Stx. How high does the antibody titer need to rise before being considered positive?
4x.
Buzzword: “Stacked-brick” appearance
Enteroaggregative E coli
Which group of E coli is typically not especially lethal, but can occasionally produce Stx exotoxin, and when it does, mortality rate is significant?
Enteroaggregative E coli
Which group of E coli are most significantly associated with brush border damage?
Diffusely adherent E coli
Which groups of E coli cause pedestal formation as part of their virulence mechanism? What are some differentiating factors?
Enteropathogenic E coli and enterohemorrhagic E coli
EPEC is more often seen in hospital nurseries and daycare centers, or resource-limited countries. It has a
Which E coli group is associated with binding mucosae of small and large intestines, causing protracted, watery diarrhea with mucus?
Enteroaggregative E coli
Which group of E coli is associated with specialized pili, LT, and ST?
Enterotoxigenic E coli
Which group of E coli tends to affect adults traveling to endemic areas?
Enterotoxigenic E coli
Which group of E coli causes significant morbidity and mortality in children < 2 YO in endemic areas, especially if they are not breast-fed?
Enterotoxigenic E coli
Which group of E coli flattens the microvilli of enterocytes?
Diffusely adherent E coli
Which group of E coli is associated with invasion via plasmid capsule antigens and causes ulcerative pathogenic lesions?
Enteroinvasive E coli
