The prevalence of verocytotoxin-producing Escherichia coli (VTEC) and E. coli O157:H7 in beef in Sweden determined by PCR assays and an immuno-magnetic separation (IMS) method
1998
Lindquvist, R. | Antonsson, A.K. | Norling, B. | Persson, L. | Ekstrom, A.C.L. | Fager, U. | Eriksson, E. | Lofdahl, S. | Norberg, P.
The number of cases of enterohaemorrhagic Escherichia coli (EHEC) in Sweden has increased dramatically since 1995, but no source of the infections has been identified. The prevalence of verocytotoxin-producing E. coli (VTEC), including E. coli O157:H7 in imported and domestic raw beef in Sweden, was determined by PCR assays and immuno-magnetic separation (IMS, Dynal). VTEC was detected by a multiplex PCR directed at sequences on the vt1 and vt2 genes, and the prevalence of E. coli O157:H7 was estimated by the IMS assay and a SZ-PCR which detects E. coli O157:H7 (and some strains of O157:NM, O55:H7 and O55:NM). VTEC was detected in 15(.)5% (57/368) and 1(.)1% (6/543) of the imported and domestic beef samples, respectively, by the multiplex PCR. E. coli O157:H7 was detected in 0(.)3% and 2(.)4% of the imported beef samples by the IMS and SZ-PCR assays, respectively. In domestic beef E. coli O157:H7 was not detected by either method, indicating that the occurrence in Swedish beef was less than 0(.)6% with a 95% certainty. The overall prevalence of VTEC was estimated to be 4(.)0%, by adjusting for the relative proportion of imported and domestic beef in Sweden and, similarly, the overall prevalence of E. coli O157:H7 was 0(.)06% (IMS) or 0(.)5% (SZ-PCR). We propose that a useful strategy to analyse a large number of food samples for VTEC and E. coli O157:H7 is an initial screening of samples using the multiplex VT-PCR in conjunction with enrichment and buoyant density centrifugation, followed by further analyses on the fraction of VT-positive samples using either the IMS method or SZ-PCR.
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