microbio 2125 unit 5 (part 18) - Escherichia coli O157:H7

etiological agent

Escherichia coli O157:H7

Distinguishing characteristics of etiological agent:

• Most common aerobic, non-fastidious gut bacterium

• Gram-negative bacillus

• 150 strains

• Some have developed virulence through plasmid transfer, others are opportunists

• exclusively human diseases

Virulence Factor(s):

• Shiga toxin gene (acquired from Shigella)

• Heat-labile exotoxin injuring nerve cells, intestine

• Cell wall receptor enabling direct toxin delivery to host

Predisposing Factors:

• Consumption of contaminated food (beef, produce like onions)

• Contact with cattle or cattle products

• Immunocompromised states

• Surgical procedures, endoscopy, tracheostomy, catheterization, dialysis and immunosuppressant therapy (general E. coli risk)

Transmission:

• Fecal-oral route via contaminated food/water

• Low infectious dose (ID = 100 cells)

Syndrome (signs + symptoms):

• Hemorrhagic colitis (intestinal hemorrhage)

• Severe diarrhea (may be bloody)

• Hemolytic uremic syndrome (HUS) → potential kidney damage

• Traveler’s diarrhea (~70% cases)

Affected body region/system:

• Gastrointestinal tract

• Kidneys (in severe cases)

Treatment:

• Supportive care (rehydration)

• Enterotoxin inactivation where needed

• Antimicrobics for non-toxin producing E. coli infections

• Antibiotics generally avoided in O157:H7 due to risk of toxin release

Prevention:

• Food safety measures (thorough cooking of beef, washing produce)

• Hygiene after contact with cattle or farm environments

Other notes:

• Frequent agent of infantile diarrhea (E. coli overall) could lead to mortality

• Major cause of UTIs (50–80% of healthy individuals) by E. coli strains

• High-profile outbreaks linked to contaminated food items (e.g., Taylor Farms onions)

Enterohemorrhagic

causes hemorrhagic syndrome and kidney damage, infamous strain: E. coli O157:H7

E. coli O157:H7 identified how?

Rapidly identified using Rainbow Agar: O157:H7 colonies appear black

Enterotoxigenic

E. coli causes severe diarrhea due to heat-labile toxin and heat-stable toxin – stimulate secretion and fluid loss; also has fimbriae

Enteroinvasive

E. coli causes inflammatory disease of the large intestine

Enteropathogenic

E. coli linked to wasting form infantile diarrhea