Difference between revisions of "Escherichia coli"
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**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 | ||
| − | ** | + | **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 | ||
Revision as of 17:21, 21 December 2007
- 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
- Avian colibacillosis:
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
- 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