Lecture 11: E. coli O157

Question 1

E. coli is a Gram-_____ commensal found in _____.

Answer 1

1. negative
2. the intestines of warm-blooded animals

Question 2

What are the 2 types of antigens on E. coli?

Answer 2

1. O antigen
   - 49 different sugars identified
   - 187 O antigens defined
2. H antigen
   - 53 H antigens defined

Question 3

When was E. coli O157:H7 first identified?

Answer 3

1982
- Identified as the cause of bloody diarrhea from eating undercooked or raw hamburger meat

Question 4

What are the virulence factors of EHEC?

Answer 4

1. Shigella dysenteriae type 1/Shiga toxin 1 and/or Shiga toxin 2
   - Cleaves ribosomal RNA and inhibits protein synthesis
   - Activates platelets
2. LEE pathogenicity island
   - Encodes type III secretion system

Question 5

What diseases does E. coli cause?

Answer 5

• Hemorrhagic colitis (bloody diarrhea)
• Hemolytic-uremic syndrome (HUS)

Question 6

How is E. coli transmitted?

Answer 6

• Ground beef and produce are the most common vehicles for outbreaks
• Cattle harboring the bacteria do not show disease because they do not have receptors for the toxins
• Super shedders

Question 7

What are the drivers of the emergence of E. coli?

Answer 7

• Contamination of food sources: meat slaughtered and processed in large, centralized facilities
• Pathogen evolution
• Human behavior: i.e.medium rare vs well done burgers

Question 8

What did E. coli O157:H7 evolve from?

Answer 8

Most likely evolved from LEE-containing O55 EPEC strains

Question 9

What type of agar is E. coli grown on?

Answer 9

Sorbitol MacConkey agar
- Non-sorbitol fermenters (E. coli O157:H7) are colorless
- Sorbitol fermenters (almost all other E. coli) are pink