Dynabeads™ plus 3 M Petrifilm HEC™ versus Vitek Immunodiagnostic Assay System™ for detection of E. coli O157 in minced meat

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The potentially low infective dose of Escherichia coli O157 makes it necessary to be able to detect low numbers in food, and the lack of sensitivitiy of direct plating has led to the development of various enrichment and detection methods. Until now, the most selective procedure for detection of E. coli O157 isolates was the immunomagnetic separation (IMS) method. The number of sorbitol non-fermenting micro-organisms other than E. coli O157 that adhere non-specifically to the magnetic beads hampers the application of IMS. The use of IMS in conjunction with 3 M Petrifilm-HEC™ yielded EHEC O157 in 21 of 165 samples of minced meat (12.7%). Without advance application of IMS, Petrifilm plates often yield confluent growth and colonies too numerous to count. The Vitek Immunodiagnostic Assay System™ (VIDAS-ECO) showed good sensitivity when testing artificially contaminated beef samples, but only four of 21 naturally contaminated samples were recognized. The addition of 3 M Petrifilm to IMS resulted in less growth of contaminants and eliminated much of the need to test presumed colonies for confirmation. The combination of IMS with 3 M Petrifilm-HEC™ is a fast and efficient screening procedure for E. coli O157 in minced meat.

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