Microbiological monitoring of sheep carcass contamination in three Swiss abattoirs

At three Swiss abattoirs, 580 sheep carcasses were examined at 10 sites by the wet-dry double-swab technique. The aim of this study was to obtain data on microbiological contamination at the abattoirs and to develop a procedure for monitoring slaughter hygiene. Median aerobic plate counts (APCs) (log CFU/cm(2)) ranged from 2.5 to 3.8, with the brisket and neck sites showing the most extensive contamination. Enterobacteriaceae were detected on 68.1% of the carcasses and in 15.2% of the samples. The proportion of positive results ranged from 2.6% (for the hind leg and the flank at abattoir C) to 42.2% (for the perineal area at abattoir A). The percentage of samples testing positive for stx genes by polymerase chain reaction was 36.6%. A significant relationship between APC and the detection of Shiga toxin-producing Escherichia coli (STEC) was found for abattoirs A and B (depending on sampling site), whereas a significant relationship between Enterobacteriaceae and STEC detection was confirmed only for abattoir A (P < 0.05). In 57.1% of the 56 isolated non-O157 strains, stx2 genes were detected, and most of them were stx2d positive. Additional virulence factors were detected in 50% of the STEC strains, with 8.9% of these strains being eae positive, 50% being EHEC-hlyA positive, and 3.6% being astA positive. For the determination of carcass contamination, the monthly examination of 10 sheep carcasses for APC and Enterobacteriaceae counts in the neck, brisket, and perineal areas is recommended. This procedure is a valuable tool for the verification of slaughter hygiene according to hazard analysis critical control point principles.