Introduction and Objectives: Staphylococcus aureus is considered as an important pathogen causing a wide range of diseases in humans and animals. The most important infection in animals is bovine mastitis. Since 1942, after two years of the discovery of penicillin, Staphylococcus aureus became resistant to penicillin. Later in 1959, the first MRSA had emerged. MRSA was first reported in 1972 in bovine mastitis. Materials and Methods: In our study 75 Staphylococcus aureus isolates from clinical mastitis in cattle confirmed by the biochemical tests and then tested for five antimicrobials include: penicillin, cefoxitin, norfloxacin, trimethoprim-sulfamethoxazole, and tylosin by disc diffusion method according to CLSI protocols. Finally, the presence of mecA, B and C genes was screened by three different PCR assays. Results: Resistance was highest against penicillin (n=44; %58.66), trimethoprim-sulfamethoxazol (n=28; %21) and tylosin (n=11; %14.6), but low to cefoxitin (n=3; %4) and norfloxacin (n=0; %0). In phenotypic test, only 3 strains were reported as MRSA (resistant to cephoxitin according to CLSI recommendations, 2018). Only one MRSA isolate harbored the mecA gene in PCR assay. Conclusion: Our study results show that most tested antibiotics can still be used for treatment of subclinical mastitis in cattle. Although the MRSA isolation rate was not high in the region comparing to some previous studies, stewardship strategies must be implemented to prevent the spread of resistant MRSA clones in animals. It is not clear if new genetic mechanisms are attributed to methicillin resistance in S. aureus in Iran.

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