Enumerating E. coli and Coliforms with Lab M's Dual Chromogenic Medium

With its applications in industrial, food and dairy environments, Lab M's Harlequin™ E.coli/Coliform Medium supports the quick and easy simultaneous enumeration of Escherichia coli and coliforms in food and environmental samples, on a single medium.

This dual chromogenic medium produces easily distinguishable colony types, even in the presence of other organisms, or when large numbers are observed, for straightforward counting, evaluation and identification.

Based upon the formulation of Tryptone Bile Agar LAB072, the medium has been modified by the addition of two chromogenic substrates, one to detect the Ss-glucuronidase enzyme (X-glucuronide) and another to detect the Ss-galactosidase enzyme (magenta-Ss-gal).

Typical E.coli strains possess both enzymes but only cleave the X-glucuronide substrate, thereby producing blue-green colonies. Typical coliforms, however, possess only the Ss-galactosidase enzyme and produce rose-pink colonies.