Abstract
In the present study, a total of 120 milk samples (50 clinical and 70 subclinical mastitis cases) collected from buffaloes located at different localities at El behera Governorate, Egypt were examined phenotypically and genotypically for the presence of S. aureus and coagulase-negative staphylococci. Results showed that 42 S. aureus and 20 coagulase-negative Staphylococcus species isolates were recovered from the examined 120 milk samples. A total of 40 S. aureus and coagulase-negative staphylococci were further identified based on the amplification of 16S rRNA, coa, clfA, and nuc encoding genes. Results revealed that all S. aureus isolated from clinical and subclinical cases were found to harbor 16S rRNA, coa, clfA, and nuc encoding genes. Resistance against 12 antibiotics was determined using disc diffusion methods. All the tested S. aureus and coagulase-negative staphylococcal isolates exhibited resistance to amoxicillin, ampicillin, cefotaxime, ciprofloxacin, cloxacillin, oxacillin, lincomycin, penicillin, and trimethoprim/sulphamethoxazole. Constitutive production of mecA and blaZ encoding resistance against penicillin and cloxacillin was reported in 70% and 20% of S. aureus and 80 % and 30% of the coagulase-negative staphylococcal isolated from clinical and subclinical mastitis, respectively. In contrast, all isolates found to harbor the specific amplicon of the sul1 gene. The amplicon of aac-aph encoding resistance gene was observed in only 6 S. aureus isolates. The specific amplicon of norA gene was detected in 4 S. aureus and 2 coagulase-negative staphylococcal isolates recovered from clinical mastitis. To conclude, the emergence of multi-drug resistant S. aureus and coagulase-negative staphylococci as a cause of mastitis in dairy farms is of public health concern requires further investigations.

Key words: Buffaloes, mastitis, S. aureus, coagulase-negative staphylococci, antimicrobial resistance genes