Coliform bacteria are the commonly-used bacterial indicator of the sanitary quality of foods and water. They are defined as rod-shaped Gram-negative non-spore forming organisms ... Coliforms are abundant in the feces of warm-blooded animals, but can also be found in the aquatic environment, in soil and on vegetation. In most instances, coliforms themselves are not the cause of sickness, but they are easy to culture and their presence is used to indicate that other pathogenic organisms of fecal origin may be present. Fecal pathogens include bacteria, viruses, or protozoa and many multicellular parasites.
Source: Wikipedia