Coloured scanning electron micrograph (SEM) of E. coli (Escherichia coli), dividing, haemorrhagic 0157:H7 strain. Escherichia coli is a Gram-negative, facultatively anaerobic, enteric, rod prokaryote. 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. Magnification: x6, 180 when shortest axis printed at 25 millimetres.