Prevalence of STEC and EHEC in French Beef

A set of 1739 beef samples composed of ground beef and carcasses were collected from routine screening using the GeneDisc array (Pall GeneDisc, Bruz, France) at the Veterinary Departmental Laboratory of Touraine, France during a 1-year period as well as in meat production plants. For this study, sampling was biased to get greater numbers of DNA samples positive for stx alone (n = 306), positive for stx and eae (n = 180), positive for eae alone (n = 200), and negative for both stx and eae (n = 1053). This sampling scheme does not represent the prevalence of STEC and EHEC in French beef. All samples were incubated in buffered peptone water (BioMerieux, Marcy l'étolie, France) for 18–24 h at 37°C. After enrichment, DNA was extracted from 1 ml of enriched sample using the InstaGene matrix (Bio-Rad Laboratories, Marnes-La Coquette, France) following manufacturer's instruction and DNA was stored at −20°C until use. When samples were found positive for stx, eae, and rfbE_O157, isolation of strains was attempted by local laboratories for confirmation of EHEC O157:H7. Following the recommendation of the French ministry of agriculture the appropriate sanitary measures were taken in positive cases of EHEC O157:H7. Unfortunately, because this study was performed several months after the samples were collected, the original samples were not conserved to attempt isolation from presumptive positives with the alternate methods described in this study.