Escherichia coli

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• Enterotoxigenic E.coli contributes to undifferentiated neonatal calf diarrhoea, a mixed viral enteritis in calves.
• Colibacillosis.
• Histiocytic ulcerative colitis in the dog and cat.
• Causes secretory diarrhoea
• Causes peritonitis in dogs and peritonitis in pigs
• In osteomyelitis
• In neonatal polyarthritis of calves
• In arthritis of horses

Eschericia coli (E. coli) overview

• Member of Enterobacteriacae family of Gram-negative bacilli
• Facultative anaerobe
• One of predominant bacterial species in colonic flora
• Abundant in the environment
• Found in many non-specific, endogenous infections, eg. wound infections and upper respiratory tract infections and septicaemia
• Also and enteropathogen

E. coli characteristics

• Oxidase negative (do not possess cytochrome C oxidase)
• Grow on MacConkey agar (in presence of bile salts)
• Reduce nitrates to nitrits and ferment glucose to produce acid and gas
• Possess a lipolysaccharide (O) antigen, a flagellate (H) antigen, polysaccharide capsule (K) antigens and fimbrial (F) antigens
• Epidemiological typing of E. coli uses antigen combinations, eg. O125:K12:H42

Extra-intestinal infection

• Soft tissue infections in adult animals
• Most common organism infecting urinary tract
• Causes pyometra in the dog and cat and pyelonephritis
• Acute mastitis in lactating animals
• Pathogenesis:
  • Produces an alpha-haemolysin which may be cytotoxic
  • Iron aquisition system
  • K antigens prevent phagocytosis or mimic host antigens and resist complement
  • Fimbriae permit adhesion to mucosal surfaces
  • May enter blood to cause septicaemia
• Clinical infections:
  • Avian colibacillosis:
    • Septicaemia in newly-hatched chickens
    • Infection enters via faecal contamination of the egg surface or via the ovary of the hen
    • Infection enters via the respiratory tract
    • A bacteraemia develops
    • Acute colisepticaemia, subacute fibrinopurulent serositis or chronic granulomatous disease of the viscera
    • Occurs in older birds via inhalation of E. coli in dust; respiratory infection spreads to the blood to cause acute colisepticaemia
    • Airsacculitis, pericarditis and perihepatitis during acute phase
    • Often secondary to virus or mycoplamsa infection or environmental stress
  • Colisepticaemia:
    • Systemic disease in young calves, piglets, foals, lambs
    • Penetration of intestinal mucosa and entrance into the blood
    • Invasive strains survive the host defences
    • Virulence related to adhesive properties, complement resistance and ability for iron aquisition
    • Ammonia, dust, viral infections and temperature changes enhance likelihood of disease

Intestinal disease

• 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
• K88 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)
• The fimbrae are encoded by plasmids
• Enterotoxigenic E. coli:
  • These strains carry a plasmid which encodes an enterotoxin
  • Two types of enterotoxin: heat-labile (LT) and heat-stable (ST) toxins
  • The plasmids which produce these toxins are responsible for the pathogenicity of these strains
  • Causes scours in pigs and calves
  • Fimbrial antigen or colonisation factor antigens (CFAs)determine species specificity
  • 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