Escherichia Coli

Question 1

commensal E. coli

Answer 1

part of normal microflora
synthesizes vitamin K
protects against other pathogens

Question 2

enteropathogenic E. coli

Answer 2

have evolved by acquiring virulence genes:

Question 3

virulence genes

Answer 3

STEC (EHEC): A/E, H, SL
EPEC: A/E, Bfp
EAEC: H, EAST
ETEC: ST, LT

Question 4

Describe A/E lesions

Answer 4

Attaching and Effacing (A/E) lesions

- induced by proteins that recruit host cell actin and impact signal transduction pathways

Question 5

What is the importance of H antigen?

Answer 5

flagella

Question 6

What is SL?

Answer 6

Shiga-Like (SL) toxin

• disrupts eukaryotic protein synthesis and is cytotoxic
• RNA cleavage activity (subunit A)
• impact cytoskeleton (subunit B)
• causes HUS (hemolytic uremic syndrome) in humans and NOT cows

Question 7

What is Bfp?

Answer 7

bundle forming pili (Bfp)

- localized adherence

Question 8

What is EAST?

Answer 8

EnteroAggregative stable toxin (EAST)

- heat stable-like toxin

Question 9

What is ST?

Answer 9

heat stable toxin (ST)

- alters cGMP levels with similar outcome to the heat-labile enterotoxin

Question 10

What is LT?

Answer 10

heat labile toxin (LT)
- targets AC leading to increased cAMP levels that results in excess Cl ion secretion and blocked Na+ uptake; leads to net loss of fluid and electrolytes into lumen of the gut and watery diarrhea

Question 11

Diagnosis

Answer 11

Lac+ (unlike S&S)
For O157:H7 (STEC): 
- cannot grow on sorbitol
- serology: O and H, toxin analysis
SL immunoassay
PCR or DNA probe analysis to identify strains
tissue culture assays
strain typing (pulsed field electrophoresis)

Question 12

Prevention

Answer 12

hay feeding: leads to higher pH and lack of acid adaptation in pathogenic E. coli

probiotics

hygiene is key

Question 13

Treatment???

Answer 13

N/A