Normal colonic flora
Virulence of strains depends on the plasmids and integrated prophage
Strain types are based on 3 antigens: O, H, K
O antigens - cell wall antigen (polysaccharide portion of the LPS)
H antigens - associated with flagella
K antigens - associated with capsule, or (less commonly) fimbriae
Transmission is by faecal-oral route.
ETEC - Common cause of traveler's diarrhoea
-> Colonisation of small intestine (pili facilitating attachment)
-> Secretion of enterotoxin, which acts on intestinal mucosa
-> Hypersecretion of Cl- ions and water, inhibited resorption of Na+
-> Significant watery diarrhoea for several days
Enterotoxin - heat-stable toxin (ST) and heat-labile toxin (LT)
ST -> elevated intracellular cGMP
LT -> elevated intracellular cAMP (identical to cholera toxin)
EPEC - Important cause of diarrhoea in infants
-> Attachment to small intestinal mucosa
-> Destruction of microvilli
-> Watery diarrhoea, and (rarely) chronic diarrhoea
EHEC - Bloody diarrhoea
-> Attachment to colonic mucosa
-> Secretion of exotoxin (verotoxin, or Shiga-like toxin)
-> Destruction of microvilli
-> Vascular endothelial damage, platelet aggregation
-> Ischemic damage to colon, kidney and others.
-> Copious bloody diarrhoea (haemorrhagic colitis)
-> Or haemolytic uraemic syndrome
Verotoxin
No mucosal invasion or inflammation.
Serotype O157:H7 most common culprit (primary reservoir -> cattle)
EIEC - Fever, bloody stool
Does not ferment lactose
EAEC - Also causes traveller's diarrhoea and persistent diarrhoea in young children
E. coli - most common cause of cystitis and pyelonephritis
Often caused by strains with P fimbriae (adherence factor)
E. coli - major cause of meningitis in <1 month old.
Associated with K1 (capsular) antigen
Motile or nonmotile
Most can ferment lactose (Lac+) (Salmonella and Shigella are Lac -ve)
All ferment glucose.
Produces acid and gas during fermentation.
Generate energy by reducing nitrates to nitrites
Oxidase negative
Facultative anaerobes
Resistance widespread
Need to obtain antibiotics sensitivity
Things to revise/add later:
Bibliography:
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Created | 20040331 |