E. coli bacterium. Coloured transmission electron micrograph (TEM) of an Escherichia coli (E. coli) bacterium in the early stages of binary fission, the process by which the bacterium divides. This Gram-negative bacillus (rod-shaped) bacterium normally inhabits the human intestines. Under certain conditions it may undergo rapid division, which increases its numbers to such an extent that it causes infection. E. coli cause 80% of all urinary tract infections, travellers' diarrhoea and gastroenteritis in children. The hair-like appendages around the bacterium are pili, structures used for bacterial conjugation. Magnification: x17,500 at 6x7cm size.