Coliform: a term used to refer to a certain group of bacteria. The coliform bacteria are rod-shaped, Gram-negative non-spore-forming bacteria. Eschericia coli (E. coli) is an example of the coliform bacteria. Coliforms are found in water, in soil, and on plants. They are common in the feces of all warm-blooded animals. Testing for coliform bacteria is commonly done to determine the quality of water supplies. While coliform bacteria themselves are not likely to cause illness, their presence in water supplies indicates that other disease-causing bacteria or organisms are present in the water supply.
Note that some rare strains of E. coli, particularly the strain 0157:H7, can cause serious illness. Recent outbreaks of disease caused by E. coli 0157:H7 have primarily been described in people who have eaten undercooked hamburger. Cases of E. coli 0157:H7 caused by contaminated water supplies are rare.