E coli

Question 1

If you were to grow a member of Escherichia coli on MacConkey agar, what would you expect to see?

Answer 1

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.

Question 2

What is a potential complication of E. coli?

Answer 2

HUS - hemolytic uremic syndrome. Complicates about 5-10% of E coli infections

Question 3

What is the treatment for uncomplicated E coli infection? What is the treatment for severe disease? What is a contraindication for this treatment?

Answer 3

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.

Question 4

What type of pili are associated with non-pathogenic strains of E coli?

Answer 4

Type 1.

Question 5

When opportunistic (not true pathogenic) E coli travel to other sites, what virulence factors are generally responsible for the inflammation that occurs?

Answer 5

LPS

a-hemolysin

Question 6

Which groups of E coli can be transmitted via fomites?

Answer 6

Those with especially low infectious doses:
EPEC (fomite transmission to kids, primarily)
EHEC

Question 7

Describe the mechanism of ETEC’s toxins

Answer 7

(Associated with enterotoxigenic E coli)

Heat labile toxin (LT) causes accumulation of cAMP.

Heat stable toxin (ST) causes accumulation of cGMP.

Question 8

Describe the mechanism of ETEC’s ST toxin

Answer 8

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.

Question 9

What virulence factors are associated with the disease commonly referred to as “Traveler’s Diarrhea”?

Answer 9

LT (heat labile)

ST (heat stable)

Question 10

Which group within E coli are NOT lactose fermenters?

Answer 10

Enteroinvasive E coli. These are very similar to Shigella spp!

Question 11

What type of pili are found on EIEC?

Answer 11

None!

Question 12

Which E coli is NOT motile?

Answer 12

Enteroinvasive E coli

Question 13

Enteroinvasive E coli typically affect what demographic?

Answer 13

Children < 5 YO in resource-limited countries.

Question 14

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)?

Answer 14

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.

Question 15

What is one difference in transmission between Shigella and EIEC?

What are some similarities?

Answer 15

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.

Question 16

What types of E coli present with diarrhea with mucous?

Answer 16

Enteropathogenic E coli

Enteroaggregative E coli

Question 17

What types of E coli are most likely to cause protracted diarrheal illness?

Answer 17

Enteropathogenic

Enteroaggregative

Question 18

Which types of E coli are associated with Stx?

Answer 18

Enterohemoragic E coli

Enteroaggregative E coli, sometimes

Question 19

Describe the main virulence factor used by enteropathogenic E coli

Answer 19

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

Question 20

What is the only E coli group we learned about with an animal reservoir? What is that reservoir?

Answer 20

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.

Question 21

Describe the virulence factors associated with enterohemorrhagic E coli.

Answer 21

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.

Question 22

Buzzword: ground meat

Answer 22

Enterohemorrhagic E coli

Question 23

Of the E coli groups we learned about, which one is primarily found in adults in industrialized countries?

Answer 23

Enterohemorrhagic E coli

Question 24

What medium is used to culture EHEC? Why, and what are the results?

Answer 24

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.

Question 25

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?

Answer 25

4x.

Question 26

Buzzword: “Stacked-brick” appearance

Answer 26

Enteroaggregative E coli

Question 27

Which group of E coli is typically not especially lethal, but can occasionally produce Stx exotoxin, and when it does, mortality rate is significant?

Answer 27

Enteroaggregative E coli

Question 28

Which group of E coli are most significantly associated with brush border damage?

Answer 28

Diffusely adherent E coli

Question 29

Which groups of E coli cause pedestal formation as part of their virulence mechanism? What are some differentiating factors?

Answer 29

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

Question 30

Which E coli group is associated with binding mucosae of small and large intestines, causing protracted, watery diarrhea with mucus?

Answer 30

Enteroaggregative E coli

Question 31

Which group of E coli is associated with specialized pili, LT, and ST?

Answer 31

Enterotoxigenic E coli

Question 32

Which group of E coli tends to affect adults traveling to endemic areas?

Answer 32

Enterotoxigenic E coli

Question 33

Which group of E coli causes significant morbidity and mortality in children < 2 YO in endemic areas, especially if they are not breast-fed?

Answer 33

Enterotoxigenic E coli

Question 34

Which group of E coli flattens the microvilli of enterocytes?

Answer 34

Diffusely adherent E coli

Question 35

Which group of E coli is associated with invasion via plasmid capsule antigens and causes ulcerative pathogenic lesions?

Answer 35

Enteroinvasive E coli