Antimicrobial resistance patterns of Staphylococcus aureus isolated from bovine subclinical mastitis in Alborz province, Iran

The aim of this study was to determine antimicrobial resistance patterns of Staphylococcus aureus isolated from bovine subclinical mastitis.California Mastitis Test was used for 2,160 quarters of 540 dairy cattle in 8 commercial dairy farms of Alborz province, Iran.Antimicrobial susceptibility test was performed by the disk diffusion method on Mueller Hinton agar.The results indicated that Staphylococcus genus was isolated from 84 out of 420 milk samples collected from suspected quarters.Out of 84 positive samples, 50 (59.5%) of them were reported as coagulase-positive S. aureus; 45 strains were further identified as Staphylococcus aureus by PCR amplification of the specific 23S rDNA gene.All S. aureus isolates showed resistance against penicillin and ceftiofur but no resistance to gentamicin, enrofloxacin and lincomycin.In addition, 38 (84.4%) of S. aureus isolates were resistant to at least 3 antimicrobial agents.According to the results ceftiofur, penicillin, ampicillin was the predominant pattern (22.2%) among seven different antimicrobial resistance patterns.Therefore, carrying out antimicrobial susceptibility tests before drug prescription seems necessary.