Escherichia coli. Coloured transmission electron micrograph (TEM) of a section through an Escherichia coli bacterium. E. coli are Gram- negative bacilli (rod-shaped) bacteria. Long flagellae enable the bacterium to move. E. coli is a normal inhabitant of the human intestine. However, under certain conditions its numbers may increase causing infection. It can cause traveller's diarrhoea" and urinary tract infections such as cystitis. E. coli is widely used in genetic studies and genetic engineering. Negatively stained. Magnification unknown."