Coliform Analyses at 30 C1

The literature directly pertinent to coliform analyses at 30 C was reviewed. Original data were presented on effects of time of incubation of violet red bile (VRB) agar plates at 30 C and the effects of autoclave-sterilization and storage of VRB agar. When boiled VRB agar was used, an incubation period of at least 24 h was required for dairy products; an incubation period of 48 h was required for water, frozen vegetables, and other materials that contained coliforms that were slow in growth initiation. Additional observations should be made after incubation of plates for another 24 h to discover if substantial increases in colony count occurred. If autoclave-sterilized VRB agar was used, the recommended incubation periods should be extended for an additional 12–24 h. The pH of prepared VRB agar should be 7.2. A pH of 6.9 or below was indicative of extensive flaws in the method of preparation and/or storage. although some deterioration occurred in the absence of marked pH changes.