Molecular characterization of enterotoxigenic and borderline oxacillin resistant Staphylococcus strains from ovine milk

Abstract

Staphylococcal enterotoxins (SEs) produced by Staphylococcus spp. are superantigens responsible for food-poisoning and are associated to mobile genetic elements such as Staphylococcus aureus pathogenicity islands (SaPI). The presence of 13 enterotoxin genes (sea, seb, sec, sed, see, seg, seh, sei, sej, sel, sek, seq, and tst) was tested in 15 S. aureus and 24 coagulase-negative Staphylococcus (CNS) multi-resistant strains isolated from ovine milk in Sardinia. All CNS isolates were enterotoxin-negative, whereas co-presence of sec, sel and tst was observed in most of the S. aureus strains. One isolate of S. aureus was characterized by tst alone. A multiplex PCR assay aimed at discriminating between the integrase genes of pathogenicity islands SaPI2, SaPIbov1, and SaPIMW2 was developed. We demonstrated that strains harboring sec, sel and tst were associated with SaPIbov1, whereas the strain positive for tst was associated with SaPI2. Borderline oxacillin resistant S. aureus strains were also detected. RAPD analysis of the Staphylococcus strains showed that clonal relationships were correlated with pathogenic profiles.