In which form do coliform bacteria indicate their presence during the fecal coliform test?

During the fecal coliform test, the presence of coliform bacteria is indicated by the production of gas. This occurs when coliform bacteria ferment lactose in a nutrient medium, leading to the release of carbon dioxide gas as a byproduct. This gas production is a key indicator that fecal coliforms, which are a specific group of bacteria commonly associated with fecal contamination, are present in the sample being tested.

The fermentation of lactose results not only in gas production but may also contribute to other changes in the medium, such as shifts in pH that could lead to a color change in some tests, though these are not the primary indicators for fecal coliform presence. The significance of gas production is that it serves as a clear and quantifiable sign of coliform activity, reinforcing the importance of gas as a marker in water quality testing and environmental health assessments.