Escherichia coli

 

 

 

Epidemiology

E. coli is an intrisic gut organism

 

Classification and Characteristics

E. coli is a gram negative bacillus occurring singly or in pairs. It is facultatively anaerobic with both fermentive and respiratory metabolism.

E. coli is highly motile and produces fimbriae for attachment.

 

Virulence Factors

Uropathogenic EC

UPEC express a number of adhesins allowing it to attach to urinary tract tissues

The K antigen leads to capsule formation, and this slime layer resists phagocytosis. K antigen correlates with propensity for pyelonephritis.

Hemolysin is also common in UPEC, though its role in virulence is unclear.

LPS, part of the gram negative cell wall, is realeased with cell death and interferes with ureteral peristalsis while stimulating a febrile response.

Type I pili - mannose sensitive hemagglutination (MSHA): help with adhesion to gut and bladder

Type II pili - P (mannose resistant) pili are the most common cause of pyelonephritis, help with sticking to bladder and kidney

UPEC can turn pili production on and off, avoiding an inflammatory response and conserving energy when not needed

 

Transmission and Infection

 

 

 

Clinical Manifesations

E. coli is the most common cause of UTIs, being responsible for up to 80% of them.

 

Diagnosis

 

 

Treatment

 

 

EHEC, usually the E coli strain O157, is associated with hemorragic colitis (HC) and hemolytic uremic syndrome (HUS), and hemolytic anemia. E coli O157 is the most common cause of kidney failure

Cattle are the principal carrier of EHEC

The infectious dose of EHEC is very low, between 1 and 100 CFU.

Most illness is associated with undercooked beef, as cattle are the primary carrier for EHEC.

E coli O157 was responsible for the Walkerton outbreak.

Treatment of E coli O157 with antibiotics

EHEC virulence factors

Flagella and fimbrial adhesins are important mediators of EHEC pathogenesis by increasing adhesion to the gut mucosa.

EHEC toxin called Shiga-like toxin (Stx) due to its similarity to Shiga toxin, produced by Shigella dysenteriae.

Following binding of the pentameric B subunit to the cell surface glycolipid Gb3, the A subunit of Stx is injected and activated. It then cleaves the 28S rRNA, inhibiting protein synthesis and resulting in cell death.

Gb3 is present on human endothelial cells and glomerular cells, resulting in HC and HUS.

EHEC also produces beta-hemolysin toxins, resulting in cytotoxicity and increased iron availablity for bacterial growth.

 

Enterotoxigenic E Coli (ETEC)

ETEC, also known as traveller's diarrhea, is characterized by watery diahhrea and vomiting.

It is caused by cholera-like toxin.

Enteroinvasive E Coli (EIEC)

 

Enteropathogenic E Coli (EPEC)

EPEC differ from EHEC due to their lack of expression of the Shiga-like toxin.

Humans are considered the primary hosts of EPEC, and outbreaks occur where locations such as day cares.