All moral rights asserted. Recolouring or alteration of the image is prohibited without permission. Coloured transmission electron micrograph (TEM) of Escherichia coli intestinal bacteria. E. coli is a Gram negative rod- shaped bacterium (bacillus). Its cell membrane is covered in fine filaments called pili or fimbriae. Hair-like structures called flagella at the rear of each bacterium provide propulsion to make it move. E. coli is a normal component of the intestinal bacterial flora, but under certain conditions some strains can cause severe infections such as gastroenteritis. E. coli has a relatively thin cell wall, which shows a typically rough structure after preparation. Magnification: x10,000 when printed at 15 centimetres tall.