Escherichia Coli

Characteristics/Epidemiology

Normal colonic flora

 

Pathogenesis/Transmission

Virulence of strains depends on the plasmids and integrated prophage

Strain types are based on 3 antigens: O, H, K

O antigens - cell wall antigen (polysaccharide portion of the LPS)

H antigens - associated with flagella

K antigens - associated with capsule, or (less commonly) fimbriae

Transmission is by faecal-oral route.

Clinical significance

Intestinal disease

Enterotoxigenic E. coli (ETEC)

ETEC - Common cause of traveler's diarrhoea

   -> Colonisation of small intestine (pili facilitating attachment)

   -> Secretion of enterotoxin, which acts on intestinal mucosa

   -> Hypersecretion of Cl- ions and water, inhibited resorption of Na+

   -> Significant watery diarrhoea for several days

Enterotoxin - heat-stable toxin (ST) and heat-labile toxin (LT)

ST -> elevated intracellular cGMP

LT -> elevated intracellular cAMP (identical to cholera toxin)

Enteropathogenic E. coli (EPEC)

EPEC - Important cause of diarrhoea in infants

   -> Attachment to small intestinal mucosa

   -> Destruction of microvilli

   -> Watery diarrhoea, and (rarely) chronic diarrhoea

Enterohaemorrhagic E. coli (EHEC)

EHEC - Bloody diarrhoea

   -> Attachment to colonic mucosa

   -> Secretion of exotoxin (verotoxin, or Shiga-like toxin)

   -> Destruction of microvilli

   -> Vascular endothelial damage, platelet aggregation

   -> Ischemic damage to colon, kidney and others.

   -> Copious bloody diarrhoea (haemorrhagic colitis)

   -> Or haemolytic uraemic syndrome

Verotoxin

No mucosal invasion or inflammation.

Serotype O157:H7 most common culprit (primary reservoir -> cattle)

Enteroinvasive E. coli (EIEC)

EIEC - Fever, bloody stool

Does not ferment lactose

Enteroadherent E. coli (EAEC)

EAEC - Also causes traveller's diarrhoea and persistent diarrhoea in young children

 

Extraintestinal disease

Urinary tract infections

E. coli - most common cause of cystitis and pyelonephritis

Often caused by strains with P fimbriae (adherence factor)

Neonatal meningitis

E. coli - major cause of meningitis in <1 month old.

Associated with K1 (capsular) antigen

Nosocomial infections (sepsis, endotoxic shock, pneumonia)

 

Laboratory identification

Motile or nonmotile

Most can ferment lactose (Lac+) (Salmonella and Shigella are Lac -ve)

All ferment glucose.

Produces acid and gas during fermentation.

Generate energy by reducing nitrates to nitrites

Oxidase negative

Facultative anaerobes

Treatment

Resistance widespread

Need to obtain antibiotics sensitivity

Treatment choices:

• Ampicillin
• Ampicillin/clavulanate
• Cefotaxime
• Ciprofloxacin
• Trimethoprim/sulfamethoxazole
• Aminoglycosides

Prevention/immunity

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Things to revise/add later:

Bibliography:

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