Prevalence and characteristics of Shiga toxin-producing Escherichia coli, Salmonella spp. and Campylobacter spp. isolated from slaughtered sheep in Switzerland

Caecum samples collected from 653 slaughtered sheep from two Swiss abattoirs were examined. The aim of this study was: (i) to determine the prevalence of Shiga toxin-producing Escherichia coli (STEC), Salmonella spp. and Campylobacter spp.; (ii) to further characterize isolated strains; and (iii) to discuss the results obtained with their relevance to food safety. The percentage of samples testing positive for STEC by a polymerase chain reaction was 29.9%. The prevalence of positive Salmonella spp. samples was 11.0% and of Campylobacter spp. 17.5%. In 55.3% of the 76 isolated non-O157 STEC strains, stx2 variants (mostly stx2d) were detected. Additional virulence factors were harbored by 55.3% of the STEC strains, 10.5% of them being eae positive, 55.3% ehxA positive and 2.6% astA positive. All isolated salmonella were identified as Salmonella enterica subsp. diarizonae serovar 61:k:1,5,(7). Pulsed-field gel electrophoresis (PFGE) was performed for genotyping and 22 different restriction endonuclease digestion profiles were found among these strains for the different farms of origin. Of the 114 isolated Campylobacter spp. strains, 64.9% were shown to be Campylobacter jejuni and 35.1% Campylobacter coli, nine strains showed resistance against tetracycline, ciprofloxacin/nalidixic acid or streptomycin. In conclusion, sheep are a reservoir for the pathogens of latent zoonoses as non-O157 STEC, S. enterica subsp. diarizonae and Campylobacter spp. The maintenance of slaughter hygiene is consequently of crucial importance. It can be measured in daily practice by “slaughter-process-controls” and regular microbiological monitoring of carcasses. These are valuable tools for verifying slaughter hygiene according to hazard analysis critical control point principles.