Animated coloured transmission electron micrograph (TEM) of Escherichia coli is a Gram-negative, facultatively anaerobic, enteric, rod prokaryote. Note the pili and fimbriae on the surface. This bacterium was isolated from the human intestine and is normally a part of the human and animal microbiota. Most E. coli strains are harmless, but some strains can cause serious problems such as: food poisoning, urinary tract infections, traveller's diarrhoea and nosocomial infections. The E. coli 0157:H7 strain is fatal to humans if contracted when contaminated meat is cooked inadequately.