Abstract
In a previous study, we showed that coagulase positive staphylococci (CPS), which are often used as indicators for S. aureus, are frequently found on pig carcasses at slaughter. Further characterization of the CPS identified only a minor part as S. aureus. Selected non-S. aureus strains were all identified as S. hyicus, However, two studies have described also in this species strains that produce staphylococcal enterotoxins. The aim of the present study was therefore to further characterize such coagulase positive S. hyicus strains isolated from pig carcasses and to assess the results also in view of their food safety relevance. A total of 189 S. hyicus strains from abattoirs A (n=36) and B (n=153) were characterized. Phenotypically, 98.9% showed non-pigmented colonies, 99.5% no haemolysis and 67.7% were egg yolk-positive. DNase activity was found in all but one isolate. Only five of the 189 strains were resistant to the antimicrobials tested. One strain harboured the mecA gene. Exfoliative toxin genes were detected in 31 (16.4%) strains. Six strains harboured the exhA and 25 strains the exhD gene. S. aureus Enterotoxin (SE) genes were detected in none of the strains.
The PFGE genotyping results show only a limited number of clusters. Cluster I included more than 50% of the strains. The fact that similar or closely related PFGE patterns of S. hyicus can be found on carcasses after bleeding in both abattoirs indicates the occurrence of widespread strains in the Swiss pig population. Moreover, the genotyping results revealed a remarkable homogeneity in S. hyicus strains isolated from different slaughter process stages in abattoir B, which could indicate a recontamination problem with persisting strains.
Hassler, C