Chromogenic Coliforms Agar (CCA) is a selective medium for the detection of E. coli and other coliforms in water and food samples. The medium contains tergitol-7 to inhibit gram-positive bacteria and some gram-negative without affecting the coliform bacteria. The coliform mixture contains Salmon-GAL and X glucuronide that change colonies color based on β-D-galactosidase and β-D-glucuronidase presence. β-D-galactosidase cleaves Salmon-GAL giving colonies a salmon-red color, while β-D-glucuronidase cleaves X-glucuronide giving them a blue color. E. coli, which has both enzymes, appears with dark blue to violet colonies. Also, the addition of tryptophan to the medium allows for Indole testing for further E. coli confirmation.
