Difference between revisions of "Escherichia coli"

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**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
 
**Causes scours in pigs and calves
 
**Causes scours in pigs and calves
**Fimbrial antigen or colonisation factor antigens (
+
**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
 +
**

Revision as of 17:06, 21 December 2007

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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