A survey of the incidence of E. coli O157 in the UK dairy industry

A survey of the incidence of Escherichia coli O157 in bovine faeces, pasteurised and unpasteurised dairy products, farm swabs and dairy factory environmental samples was undertaken. A single enrichment broth was employed, together with three detection methods, comprising a plating medium, a commercially available ELISA technique (Petrifilm) and an ELISA test under development (Organon-Teknika). For all detection methods, the efficiency of recovery, determined using artificially contaminated samples, was poor and this was attributed to the growth of competitors in the enrichment broth. Both the plating and the Organon-Teknika methods yielded a higher proportion of false positives than the Petrifilm method; however, the former two methods also detected a wider range of verotoxigenic E. coli than the Petrifilm method. Verotoxigenic E. coli were not detected in any of 1146 samples examined. The poor performance of the methodolgy may explain why the environmental incidence appears to be low although the incidence of infection by E. coli O157 is increasing.