Effects of slaughter processes on pig carcass contamination by verotoxin-producing Escherichia coli and E. coli O157:H7.

The aims of the present study were: (i) to evaluate verotoxin-producing Escherichia coli (VTEC) faecal carriage of slaughtered pigs; (ii) to determine the effects of three different pig slaughtering processes on pig carcass contamination by VTEC; (iii) to characterise the VTEC strains isolated from pig and pig slaughterhouses (virulence genes and serotype); and (iv) to compare the strains isolated in the same slaughterhouse in order to identify the routes of contamination inside the slaughterhouse. Pork carcasses from three French slaughterhouses were sampled at three steps of the slaughter process and different sites in each slaughterhouse were sampled at three different times in the work day. Faecal material from each sampled carcass, potable water and scalding water were also collected. Detection of stx genes was performed by polymerase chain reaction (PCR) on a total of 1227 samples. In addition, a second PCR specific for E. coli O157:H7 detection was carried out on the stx-positive samples. VTEC strains were recovered from positive samples by colony hybridisation or immunoconcentration, then serotyped, genetically characterised (eae, ehx, stx1, stx2, stx2c, uidA genes associated with virulence) and pulsotyped. No E. coli O157:H7 was isolated from the three uidA-positive samples. VTEC faecal carriage was 31%. Global carcass contamination decreased with slaughter process (from 46% to 15%), whereas environmental contamination increased (from 7% to 29%). No VTEC isolates harboured eae, ehx, and uidA genes. VTEC contamination routes were not clearly identified.