UTTAR PRADESH JOURNAL OF ZOOLOGY

Methicillin-resistant Staphylococcus aureus (MRSA) is a relevant bacterial pathogen in bovine mastitis and requires reliable detection because of its antimicrobial resistance profile. The present study evaluated phenotypic and molecular approaches for detecting MRSA among bovine milk isolates by comparing oxacillin disc diffusion, cefoxitin disc diffusion and PCR-based detection of the mecA gene. A total of 400 milk samples, including normal and mastitic milk from cattle and buffaloes, were examined. Overall, 202 isolates were confirmed as Staphylococcus aureus by standard microbiological methods. Phenotypic screening identified 49/202 isolates (24.25%) as MRSA by oxacillin disc diffusion, whereas cefoxitin disc diffusion detected 63/202 isolates (31.19%). Among cattle isolates, cefoxitin detected 35/111 isolates (31.53%), compared with 28/111 isolates (25.23%) detected by oxacillin. Among buffalo isolates, cefoxitin detected 28/91 isolates (30.77%), whereas oxacillin detected 21/91 isolates (23.08%). Molecular analysis showed that 56 of the 63 cefoxitin-positive isolates carried the mecA gene. The number of mecA-positive isolates was higher in mastitic milk than in normal milk from both cattle and buffaloes. These findings indicate that cefoxitin disc diffusion detected more MRSA isolates than oxacillin disc diffusion and showed close agreement with mecA gene detection. Therefore, cefoxitin disc diffusion may be a useful, simple and cost-effective phenotypic screening method for routine MRSA detection in bovine milk samples, particularly where molecular testing facilities are limited.