Occurrence and antibiotic resistance of enterotoxigenic Staphylococcus aureus in raw ovine and caprine milk in Greece

Ovine (n = 140) and caprine (n = 35) raw bulk tank milk samples from farms in central Greece were examined for the occurrence of enterotoxigenic Staphylococcus aureus. The S. aureus isolates were screened for staphylococcal enterotoxin (SE) production, the presence of enterotoxin genes, antibiotic resistance (AR), and methicillin resistance. S. aureus was isolated from 24.3% and 31.4% of ovine and caprine milk samples, respectively. Among the S. aureus isolates of ovine milk (n = 34) and caprine (n = 11) milk, the enterotoxigenic (SEA-SED) isolates were 21 (61.8%) and 7 (63.6%) for the ovine and caprine milk, respectively. Most toxigenic isolates harbored more than one toxin gene and a total of 11 distinct toxinotypes were detected. The most frequent toxin-gene combinations were "sec, tst" (8 isolates), "seb, seg, sei, tst" (4), "seb, seg, sei" (3), and "seb" (3). Six isolates displayed multiple AR towards up to five antimicrobials. Among ovine milk isolates, the highest resistance frequency was observed towards erythromycin (11.8% of the isolates) and tetracycline (8.8%). Among caprine milk isolates, the most frequent resistance was observed towards erythromycin (18.2%). One methicillin-resistant S. aureus (MRSA) isolate was detected in an ovine milk sample and belonged to spa type t4038. This spa type has been isolated for the first time in Greece and, to our knowledge, has not been previously reported among MRSA isolates from raw milk or dairy products worldwide.