E. coli bacteria. Artwork of 4 Escherichia coli bacteria, commonly known as E. coli. These Gram- negative, rod-shaped bacteria are normal inhabit- ants of the intestine of humans and other animals, and are usually harmless. Under certain conditions E. coli may increase in number & cause infection. They have long, hair-like projections (flagellae) which are used for locomotion. They have a cell wall (white) which encloses the cytoplasm (darker) containing the nuclear material. The cell wall is itself enclosed by a protective, gel-like capsule. Serotypes of E. coli are responsible for food poisoning, gastroenteritis and urinary tract infections in adults and children.