Faecal carriage of Verocytotoxin-producing Escherichia coli O157 and carcass contamination in cattle at slaughter in northern Italy

A study on the prevalence of the faecal carriage of Verocytotoxin (VT)-producing Escherichia coli (VTEC) O157 and on the rate of carcass contamination was carried out on feedlot cattle and dairy cows at slaughter in northern Italy. Between April 1998 and January 1999, 12 sampling visits were performed on different days in seven different slaughterhouses. At each visit, 5-12 animals consecutively slaughtered were selected. From each animal, faeces were collected from the rectum immediately after slaughter and surface swabs were taken from the leg region and the diaphragmatic insertion of the carcass. All samples were examined for the presence of VTEC O157 using an immunomagnetic separation technique. A total of 100 animals coming from 60 different farms were examined. In total, VTEC O157 was isolated from the intestinal content of 17, and from the carcasses of 12 of the 100 animals examined. In particular, VTEC O157 was recovered from six (35.3%) out of the 17 carcasses from which the organism had previously been isolated from rectal content and from six (7.3%) of the 82 carcasses of the stool-negative cattle. In seven carcasses, VTEC O157 was isolated from the leg area, in two carcasses from the diaphragmatic area, and in three carcasses from both areas. Major differences in the prevalence of VTEC O157 were observed in the different groups of cattle sampled. In 7 of the 12 sampling visits, all the specimens examined were negative, while 16 of the 17 positive stool samples and 11 of the 12 positive carcass swabs were collected during three of the visits, performed in June in three different abattoirs. In these three visits, the ratios between the percentage of animals carrying VTEC O157 in the stools and the percentage of contaminated carcasses were 0.33, 0.57, and 1.66, respectively; thus, confirming that slaughter practices can largely influence the rate of carcass contamination. Phage typing and PFGE analysis of VTEC O157 isolated from samples collected at the same visit suggested that both auto- and cross-contamination occurred.