Coagulase- positive Staphylococcus aureus (CPS) is a leading cause of both clinical and subclinical bovine mastitis. Moreover, methicillin- resistant Staphylococcus aureus (MRSA) have been identified as an emerging mastitis pathogen in dairy cows. In our study, 121 raw milk samples were collected from individual clinical healthy cows from five commercial farms. 52 samples (42.98%) were positively detected as CPS. Fifty-two strains of CPS were isolated and identified using phenotypic and molecular approaches. Their coagulase gene (coa gene) amplification showed a single amplicon of a size between 600 and 1000 bp. Five CPS isolated strains from YZ farm, which was resistant to oxacillin and contained a specific 310-bp for the mecA gene, were identified as MRSA. The staphylococcal enterotoxin a (SEa) gene was detected in 18 strains. None of the isolates carried the gene SEb, SEc, SEd and SEe. All isolates including the five MRSA isolates were uniformly susceptible to Cephalothin (KF), Ofloxacin (OFX) and Vancomycin hydrochloride (VA) at minimum inhibitory concentrations (MIC). Besides P and CIP, the resistance of these isolates resistances to Oxacillin (OX), rifampicin (RIF), Cefotaxime (CTX), Azithromycin (AZM) and Clindamycin (DA) were relatively low (<20%). Together, our findings demonstrated that there was high prevalence of CPS and ten MRSA contaminations in raw milk from clinical healthy cows.

Key words: Antimicrobial resistance, coa gene, Coagulase-positive S. aureus (CPS), MRSA, Raw milk, Staphylococcal enterotoxin (SE) genes