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)-prod ucing Escherichia coli (VTEC)O157 and on the rate of carcass contamination was: curried out on feedlot cattle and dairy cows at slaughter in northern Italy. Between April 1998 and January 1999. 12 sampling visits were perform ed on different days in seven different slaughterhouses. At each visit, 5-1 2 animals consecutively slaughtered were selected. From each animal, farces were collected from the rectum immediately after slaughter and surface swa bs were taken from the leg region and the diaphragmatic insertion of the ca rcass. All samples were examined for the presence of VTEC O157 using an imm unomagnetic separation technique. A total of 100 animals coming from 60 dif ferent farms were examined. In total, VTEC O157 was isolated from the intes tinal content of 17, and from the carcasses of 12 of the 100 animals examin ed. In particular. VTEC O157 was recovered from six (35.3%) out of the 17 c arcasses from which the organism had previously been isolated from octal co ntent 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 carca sses from the diaphragmatic area, and in three carcasses from both areas. M ajor differences in the prevalence of VTEC O157 were observed in the differ ent groups of cattle sampled. In 7 of the 12 sampling visits, all the speci mens 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 visi ts, performed in June in three different abattoirs. In these three visits, the ratios between the percentage of animals carrying VTEC O157 in the stoo ls and the percentage of contaminated carcasses were 0.33, 0.57, and 1.66, respectively: thus, confining that slaughter practices can largely influenc e 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 occurr ed. (C) 2001 Elsevier Science B.V. All rights reserved.