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*Facultative anaerobe
*Facultative anaerobe
*One of predominant bacterial species in colonic flora
*One of predominant bacterial species in colonic flora
*Colonisation of intestinal tract from environmental sources shortly after birth
*Abundant in the environment
*Abundant in the environment
*Most strains have low virulence
*Found in many non-specific, endogenous infections, eg. wound infections and upper respiratory tract infections and septicaemia
*Found in many non-specific, endogenous infections, eg. wound infections and upper respiratory tract infections and septicaemia
*Also and enteropathogen
*Also and enteropathogen
*Pathogenic strains possess virulence factors allowing colonisation of mucosal surfaces
*Epidemiological typing of ''E. coli'' uses antigen combinations, eg. O125:K12:H42
*Epidemiological typing of ''E. coli'' uses antigen combinations, eg. O125:K12:H42
===Pathogenesis===
*Virulence factors include capsules, endotoxin, enterotoxins and colonisation factors
*Capsular polysaccharides produced by some strains prevent phagocytosis and interfere with complement
*Endotoxin is a lipolysaccharide component of the cell wall of Gram-negative bacteria, composed of lipid A, a core polysaccharide and various side chains
*Endotoxin is realeased when bacteria die, and causes endothelial damage leading to disseminated intravascular coagulation and endotoxic shock; it is also a pyrogen
*
===Extra-intestinal infection===
===Extra-intestinal infection===
*''E. coli'' is part of the flora of the large intestine, but is not usually found in the small intestine
*''E. coli'' is part of the flora of the large intestine, but is not usually found in the small intestine
*Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species
*Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species
*K88 is associated with adhesion to the small intestinal mucosa of pigs
*K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs
*K99 associated with adhesion in pigs and cattle (these possess certain fimbrae, and are now renamed F antigens)
*K99 (F5) associated with adhesion in pigs and cattle (these possess certain fimbrae, and are now renamed F antigens)
*The fimbrae are encoded by plasmids
*The fimbrae are encoded by plasmids
*''E. coli'' may cause diarrhoea via attaching and efacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli
*''E. coli'' may cause diarrhoea via attaching and efacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli
**The plasmids which produce these toxins are responsible for the pathogenicity of these strains
**The plasmids which produce these toxins are responsible for the pathogenicity of these strains
**Fimbrial antigen or colonisation factor antigens (CFAs)determine species specificity
**Fimbrial antigen or colonisation factor antigens (CFAs)determine species specificity
**Fimbrial adhesins allow bacteria to attach to mucosal surfacesin the small intestine and lower urinary tract; this prevents expulsion by peristalsis and flushing of urine
**LT is an oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer)
**LT is an oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer)
**It attaches to the brush border of the epithelial cells of the small intestine
**It attaches to the brush border of the epithelial cells of the small intestine
*Enterohaemorrhagic ''E. coli'':
*Enterohaemorrhagic ''E. coli'':
**Possibly carried by cattle
**Possibly carried by cattle
**Produce shiga-like toxin, a vero toxin, especially O157:H7
**Produce shiga-like toxin, a vero toxin
**Attaching and effacing lesions, unrelated to toxin production
**Attaching and effacing lesions, unrelated to toxin production
**Disseminated intravascular coagulation and thrombus formation
**Disseminated intravascular coagulation and thrombus formation
**Cause haemorrhagic collitis and haemolytic/uraemic syndrome in humans
**''E. coli'' O157:H7 causes haemorrhagic collitis-haemolytic uraemic syndrome in humans
*Enteroaggretative ''E. coli'':
*Enteroaggretative ''E. coli'':