RAPID’E.coli 2 medium is a selective chromogenic agar used for direct enumeration, without confirmation of colonies, of Escherichia coli and other coliforms in food products and environmental samples. The medium is validated by AOAC, AFNOR and NordVal.
The medium is based on simultaneous detection of β-D-Glucuronidase (β GLUC) and β-D-Galactosidase (β GAL). E.coli (GAL+/GLUC+) forms violet to pink colonies; other coliforms (GAL+/GLUC–) form blue to green colonies. Observation of gas bubbles is not necessary for differentiation of E. coli from other coliforms. Detection of GLUC confers a high specificity to the culture medium. E. coli is one of the only species of Enterobacteriaceae to possess this enzyme. Most interfering flora are inhibited, especially at 44°C, giving the medium high specificity. Two easy protocols are validated, a single layer and a single plate per dilution for enumeration of E.coli at 44°C and enumeration of E.coli and coliforms at 37°C with a single layer on the same plate.