Escherichia coli O157:H7 visual immunoprecipitate assay: a comparative validation study

A wide variety of food products, with emphasis on raw meat products, were analyzed simultaneously by 3 methods: the Escherichia coli O157:H7 (EHEC) visual immunoprecipitate assay (VIP), the Assurance EHEC enzyme immunoassay, and a modified Bacteriological Analytical Manual (BAM) culture method. This paper reports results of a comparative study of the VIP and modified BAM methods. In this comparative study, 1050 samples and controls gave false-negative rates of 1.0 and 0%, respectively, for the VIP and the modified BAM culture methods. The overall agreement between the 2 methods was 99.4%. Cultural confirmation of presumptive positive samples was problematic because competitive flora were present in higher levels than EHEC in the enrichment broth after incubation and the target organism had nondescript characteristics on the primary selective agar, hemorrhagic coli agar, which necessitated picking of additional colonies in many instances.