In the context of culturing on Endo Total Coliform Broth, if a colony grows red without a metallic sheen and does not react on MacConkey medium, it is unlikely to be a true coliform. Coliforms typically produce a metallic sheen on Endo agar and ferment lactose on MacConkey agar, leading to pink colonies.
To confirm whether the organism is a coliform or not, you can perform the following confirmatory tests:
Lactose Fermentation Test: Inoculate a lactose broth and check for gas production and acid production after incubation. Coliforms will typically ferment lactose, producing gas.
Indole Test: Some coliforms, like Escherichia coli, are indole positive. Use tryptone broth and check for indole production.
Citrate Utilization Test: Determine if the organism can utilize citrate as its sole carbon source. Most coliforms cannot.
Methyl Red Test: This test checks for mixed acid fermentation. Coliforms typically show a positive result.
Voges-Proskauer Test: This test checks for acetoin production. Most coliforms are negative.
Coliform chromogenic agar: On CCA, coliforms grow as pink to red colonies, and E. coli produces dark-blue to violet color.



