Escherichia coli O157:H7 in slaughtered cattle. A surveillance study in the Ravenna District (North of Italy)

This study was aimed at evaluating the prevalence and characterize strains of verotoxigenic Escherichia coli serotype O157 in faeces and carcasses of cattle slaughtered in an industrial slaughterhouse located in North of Italy (Ravenna Province). Beef carcasses and faeces of fifty-five animals were sampled between December 2001 and April 2003 in a commercial abattoir slaughterhouse located in North of Italy (Ravenna Province). Sampling was performed on 5 animals per day, approximately at half of working period, for eleven months. Carcass samples were taken by excision following destructive method described in the EC Directive 471/2001 and faecal material was taken from the colon. Probability of being carriers of VTEC and of having contaminated carcasses are respectively p1 = 17.54% (C.L. 10-26%) and p2 = 5.26% (C.L. 1-11%). This prevalence is relatively high, but similar to those recently observed in Italy. Our investigation confirmed that slaughtering of infected cattle pose a risk of cross-contamination of carcasses. It also showed that isolates can show mutations with loss of the gene for Vtx2 upon sub-cultivation and this can pose some problems in diagnosis