Escherichia coli

From WikiVet English
Jump to navigation Jump to search
BACK TO ENTEROBACTERIACEAE
BACK TO BACTERIA
BACK TO INFECTIOUS AGENTS AND PARASITES

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
  • 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
  • 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
    • LT causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes
    • This causes irreversible activation of adenylate cyclase in target cells
    • This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium
    • The gut becomes distended with fluid and a diarrhoea which lasts several days results
    • LT is antigenic
    • Immunity is developed via production of antibody to LT protein and fimbrial antigen
    • Parenteral vaccination of pigs and cattle protects offspring from scours via antibody production in the colostrum (passive immunity)
    • ST is not immunogenic; it is small, with only 19 amino acids
    • ST activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion
  • Enteropathogenic E. coli:
    • Possess E. coli adherencefactor plasmid
    • Cause attching and effacing lesions in the gut
  • Enteroinvasive E. coli
    • Dysentry-like strains
    • Invade epithelial cells by inducing endocytosis
    • Traverse gut wall to lamina propria
  • Enterohaemorrhagic E. coli:
    • Possibly carried by cattle
    • Produce shiga-like toxin, a vero toxin, especially O157:H7
    • Attaching and effacing lesions, unrelated to toxin production
    • Disseminated intravascular coagulation and thrombus formation
  • Enteroaggretative E. coli:
  • Oedema disease of pigs:
    • Associated with oedema disease toxin-producing strains of E. coli
    • Verotoxin released in the small intestine and carried in the bloodstream
  • Haemorrhagic gastroenteritis:
  • Watery mouth of lambs:
    • Lack of colostrum allows collonisation and overgrowth of E. coli in the small intestine
    • Absorption of endotoxin leads to death