If there was a prize for the most maligned bug of the last decade of the 20th Century then Escherichia coli would be a serious contender. Under normal circumstances it is a perfectly innocuous commensal of the gut. The trouble is that some strains have picked up a few nasty habits by acquiring certain plasmids. The least troublesome of these are called Enteropathogenic E.coli or EPEC for short. They stick to intestinal mucosa and strip off (efface) the microvilli, a process known as "attachment-effacement". This
wrecks the integrity of the gut wall causing large amounts of fluid to be lost leading to diarrhoea. EPEC can be recognised in samples of faeces because they carry special antigens (one is called K88) on the tip of their Type I fimbriae. Whereas an EPEC infection might be just mildly unpleasant to healthy adults, it can be quite devastating to young children, babies and the old especially in developing countries where access to rehydrating facilities is limited or absent.
Other E.coli strains have learned how to make toxins and are known as Enterotoxigenic E.coli (ETEC). These also stick to gut mucosal cells but cause fluid loss via the toxin they produce. Two types of toxin have been recognised, one is heat stable (ST) and the other is heat labile(LT).
ETEC are very serious pathogens of babies and young children in developing countries.
Another type of toxin-producing E.coli are strains which produce a powerful toxin known as "Verotoxin" or "Verocytotoxin". These are known as Vero cytotoxin-producing E.coli (VTEC) and cause damage directly by stripping off microvilli just like EPEC (attachment-effacement) as well as via their verotoxin.
The best know strain of VTEC is E.coli serotype 0157 which caused the serious food-poisoning outbreak in Scotland recently.
The final type are Enteroinvasive E.coli (EIEC) which attach to the large intestine mucosa and invade cells by being taken in by endocytosis. Once inside they multiply and spread causing damage and inflammation.
The one thing ALL these pathogens have in common is Type I fimbriae which they use to attach to the gut mucosal cells.
If you have trouble in imagining just how serious infections with some of these strains can be, then remember, the illnesses they cause can be just as dangerous as cholera
