Escherichia coli

• associated with variety of disease, including sepsis, UTIs, meningitis, and gastroenteritis.

Many antigens (O,H,K) have been epidemiologic purposes.

1. E. coli-associated diarrheal diseases

• Extremely common worldwide.

1) Enterotoxigenic E coli (ETEC)

Site of action: small intestine, secretory diarrhea

A common cause of "traveler's diarrhea", most common bacterial etiology of acute bacterial diarrhea worldwide.

Produce one or both of two protein toxins

A. Heat-labile exotoxin (LT): just like cholera toxin.

subunit B - attaches to the G_M1 ganglioside and facilitates the entry of subunit A  activates adenylyl cyclase  increase cAMP  prolonged hypersecretion of water and electrolyte imbalance diarrhea

B. Heat-stable enterotoxin (ST) :

ST_a : Activates guanylyl cyclase and stimulate fluid secretion.

ST_b : Stimulates cyclic nucleotide-independent secretion.

2) Enteropathogenic E coli (EPEC)

Site of action: small intestine, secretory diarrhea

Major cause of diarrhea in infants, rare in older children and adults.

Outbreaks of diarrhea in nurseries in developed countries

Bacterial attachment to epithelial cells of the small intestine by chromosomally mediated factor  effacement (destruction) of the microvillus  malabsorption due to microvilli destruction  diarrhea

3) Enteraggregative E coli (EAEC)

Site of action: small intestine, secretory diarrhea

Acute and chronic diarrhea in developing countries

Aggregation on epithelium of the small intestine by aggregative adherence fimbriae I and II which are carried on a plasmid  shortening of the microvilli, mononuclear infiltration  stimulate secretion of mucus, malabsorption  diarrhea

4) Enterohemorrhagic E coli (EHEC)

Site of action: large intestine, inflammatory diarrhea

Secrete the powerful Shiga-like toxin (verotoxin)

Verotoxin ; same mechanism of action as the Shigella toxin

Inhibit protein synthesis by inhibiting the 60S ribosome  intestinal cell death  bloody diarrhea (hemorrhagic), abdominal cramps

Hemolytic uremic syndrome (HUS, acute renal failure (uremia), microangiopathic hemolytic anemia, thrombocytopenia) is associated with a strain of EHEC, called E.coli O157:H7

Prevent by thorough cooking of ground beef

5) Enteroinvasive E coli (EIEC)

Site of action: large intestine, inflammatory diarrhea

The virulence factor encoded by plasmid mediated invasion to the epithelial cells --> host tries to get rid of the invading bacteria --> immune mediated inflammatory reaction with fever

organism	Enteric syndrome	site of infection	Bloody stools	Fecal WBC	pathogenic Mx	Extraintestinal manifestation
EIEC	inflammatory	Colon	+	++	Invasion & inflammation	rare
EHEC
			++	0	Epithelial effacement & verotoxin	HUS, thrombocytopenic purpura

Treatment

No single specific therapy is available

Epidemiology, Prevention, & Control

Most infections are endogenous (patient's normal microbial flora)

Strains causing gastroenteritis are generally acquired exogenously

Infections are controlled by use of appropriate infection-control practices to reduce the risk of nosocomial infections (e.g., restricting use of antibiotics, avoiding unnecessary use of urinary tract catheters)

Maintenance of high hygienic standards to reduce the risk of exposure to gastroenteritis strains

Proper cooking of beef products to reduce risk of EHEC infections

Category: Microbiology Notes