No abstract

Three direct plating methods to enumerate Escherichia coli from food in 24 h are described. Unlike the majority of enterics, 96% of E. coli are able to cleave β‐glucuronic acid. This reaction can be observed by incorporating (1) 4‐methylumbelliferyl‐β‐D‐glucuronate, (2) para‐nitrophenyl‐β‐D‐glucuronate or (3) 5‐bromo‐4‐chloro‐3‐indolyl‐β‐D‐glucuronate (BCIG) into a peptone tergitol agar base. Escherichia coli produce fluorescent, yellow or deep blue colonies from these three compounds respectively. BCIG agar proved the easiest to read and produced the least number of false positives and false negatives. An attempt is made to explain the poor correlation achieved between this method and a conventional most probable number technique.

A comparative study was made of the ability of three commercial identification kits to confirm the identity of motile aeromonads isolated from foods. The kits included the API 20E, API 20NE and Microbact 24E. The results showed that both the API 20NE and Microbact 24E correctly identified 97.5% of isolates but the API 20E only 72.5%.