First report on genotypic estimation of MRSA load in udder of nomadic sheep flocks affected with subclinical mastitis in Pakistan.

Mastitis is one of the highly devastating issues responsible for production and economic losses in all dairy animals including sheep. This study was designed to investigate subclinical mastitis (SCM) associated with S. aureus in lactating nomadic ewes, along with the associated risk factors analysis. Furthermore, molecular characterization and antibiogram profiling of local methicillin-resistant S. aureus (MRSA) isolates of ovine origin were also performed. A total of 384 milk samples (n = 384) were collected from 13 nomadic sheep flocks using a convenient sampling technique. SCM was evaluated using a Surf Field Mastitis test and the S. aureus was isolated using standard microbiological techniques. Kirby-Bauer disc diffusion assay was used for phenotypic identification of MRSA while the mecA gene was tested through PCR. Study results revealed that SCM was prevalent at 34.37% while S. aureus association was recorded at 39.39%. MRSA prevalence was 36.53% and 21.15% using phenotypic and genotypic tests, respectively. The mecA gene sequences of study isolates showed maximum resemblance with already reported sequences from Pakistan, China, and Myanmar. MRSA isolates showed maximum resistance towards penicillin, ceftriaxone sodium, and trimethoprim + sulphamethoxazole while gentamicin, ciprofloxacin, and tylosin showed maximum efficacy. Risk factors analysis revealed that various flock management, housing, and host-related factors positively influenced the incidence of S. aureus-associated SCM. This study is the first report on the prevalence of S. aureus and MRSA associated with SCM in lactating ewes in Pakistan. This study will help to devise effective treatment and control strategies for S. aureus-associated SCM.