What does coliform mean?
A coliform is any of a group of rod-shaped bacteria that live naturally in the intestines of humans and warm-blooded animals, with Escherichia coli being the most famous member. The term comes from the word colon combined with the suffix '-form', literally meaning 'colon-shaped' or 'resembling the colon bacillus'. Because these organisms are shed in feces in enormous numbers but rarely survive long outside the body, their presence in drinking water, swimming areas, or food is treated as strong evidence of recent sewage or animal-waste contamination. This makes coliform testing a cornerstone of modern public health: municipal water systems routinely report 'total coliform counts', and beaches close when fecal coliform levels climb too high. Used almost entirely in technical, regulatory, and environmental contexts, the word functions both as a noun ('coliforms were detected in the sample') and as a modifier ('a coliform count'). Its everyday relevance lies less in conversation than in the invisible role it plays in keeping tap water and food supplies safe.
A rod-shaped, Gram-negative bacterium that inhabits the intestines of humans and warm-blooded animals; collectively, such bacteria used as indicators of fecal contamination in water and food.
"Water samples from the well tested positive for coliforms."
Usually pluralized when referring to bacteria generally; singular use often names the group as a whole.
Relating to, resembling, or composed of such bacteria; typically used attributively before another noun.
"The laboratory reported a high fecal coliform concentration at the swimming site."
The standard English plural, used when referring to multiple individual bacteria of the group.
"Coliforms were present at levels exceeding the safety threshold."
When scientists say water is 'safe to drink,' they usually mean it passed a test for coliforms — bacteria named not for what they are, but for where they live: your colon.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of coliform
The word coliform was formed in the late nineteenth century from the Latin word for the large intestine, colon (itself borrowed from Greek kolon), joined to the suffix '-form', meaning 'having the shape or form of'. It originally described bacteria resembling Bacillus coli, now known as Escherichia coli, the organism identified in the intestines by Theodor Escherich in the 1880s. Related English derivatives of the same root include colic, colitis, and colostomy, all referring to the colon.
How coliform is actually used
Almost always encountered in technical, public-health, or environmental contexts rather than casual conversation. In scientific writing it appears both as a standalone noun ('coliforms were detected') and attributively ('a coliform colony'). The plural 'coliforms' is standard when referring to multiple bacteria.
Easily confused with coliform
E. coli is one specific species within the broader coliform group, which also includes other genera such as Klebsiella and Enterobacter.