In the multi-tube fermentation method, what type of culture media is used in the confirmed test?

The multi-tube fermentation method, commonly used to identify and confirm the presence of coliform bacteria such as Escherichia coli in water samples, relies on selective culture media that can facilitate the growth of these bacteria while inhibiting others. In this context, the confirmed test specifically employs green lactose bile broth as it is designed to support the fermentation of lactose while containing indicators for the production of gas, which is a helpful measure of coliform presence.

Green lactose bile broth contains bile salts that inhibit the growth of non-coliform organisms, making it particularly useful in confirming the presence of coliforms. The lactose component allows for the detection of lactose fermenters, which produce acid and gas, indicating positive fermentation. This medium is also utilized for its ability to provide a definitive confirmation when coliforms are suspected from preliminary tests in the multiple-tube fermentation technique.

Other media, while useful in different testing contexts, do not serve the specific purpose of confirming coliforms in this particular method. For instance, bromothymol blue broth is typically used as an indicator for pH changes but lacks the appropriate selective features for coliform confirmation. MacConkey agar can differentiate lactose fermenters but is often not used as a confirmed test in the multi