Coliform bacteria are a group of aerobic, rod-shaped bacteria originating in the faeces of warm-blooded animals and the environment, used as hygiene indicator organisms in food and water testing. Their presence suggests faecal contamination or poor sanitation, though not all coliforms are harmful: the group includes the faecal indicator Escherichia coli, some strains of which cause serious illness. Water suppliers and food manufacturers test for total coliforms and E. coli routinely, with legal limits set for drinking water and many foods. Finding them triggers investigation of sources, from contaminated ingredients to dirty equipment or handlers.