E. coli-Coliforms Chromogenic Medium 500g Condalab 1340

The E. coli-Coliforms Chromogenic Medium is for the detection of E. coli and other coliforms in waters and foods. The recovery and enumeration of Escherichia and coliforms are important indicators  of environmental and food hygiene. Ingredients in this medium, such as peptone, sorbitol and pyruvate interact for quick colony growth, including infectious coliforms and allows the recovery of sublethal thermally injured coliforms.

There is tergitol-7 inhibits gram-positive bacteria and some gram-negative without impacting the coliform bacteria. Sodium chloride maintains the osmotic balance and phosphate salts act as a buffer system and bacteriological agar is the solidifying agent that is used.

Detection of ß-glucuronidase is widely used to differentiate Escherichia coli, as the enzyme is present in E. coli but not in other member of coliform
group. The chromogenic mixture contains chromogenic substrates: Salmon-GAL and X-glucuronide. Coliform enzymes produced, ß-D-galactosidase and
ß-D-glucuronidase, cleave these substrates resulting in the different coloration of bacteria colonies. The ß-D-galactosidase cleaves Salmon-GAL
substrate, and gives a salmon-red color to the coliform colonies. The ß-D-glucuronidase, enzyme characteristic of E. coli, cleaves X-glucuronide, giving a
blue color to these colonies.

E. coli has the two enzymes and cleaves both chromogenic substances giving dark blue to violet colonies. Total coliforms are the sum of E. coli colonies plus salmon-red colonies. The addition of tryptophan to the medium allows the performance of the Indole test for further E. coli confirmation.

Note: Some Shigella strains contains the enzyme ß-D-glucuronidase and can grow aslight blue colonies. The negative E. coli b-ß-glucuronidase colonies
are Salmon, e.g. E. coli O157:H7.