Abstract
Subclinical mastitis primarily with microbial etiology is amenable to different antibiotic therapy and the outcome is doubtful
due to the association of a variety of microorganisms, host-specificity and continual evolution of different antibiotic-resistant
strains of microorganisms. Therefore, the present study was ascertained to investigate the presence, genotypic characteristics
of Staphylococcus aureus isolates recovered from subclinically mastitic Cholistani cattle and the effectiveness of different
antibiotics against these pathogens by disc diffusion technique. For this purpose milk samples were collected from a total of
1457 lactating Cholistani cattle and screened for mastitis using California Mastitis Test. All the positive samples were
processed for culturing. Staphylococcus aureus isolates isolated and identified on the basis of colony characteristics, coagulase
test, biochemical features and amplification of spa (spa-X) and coagulase (coa) genes. The results of PCR revealed that
amplification of spa (spa-X) gene yielded different PCR products (400bp and 350bp) while coagulase (coa) produced different
products size (390bp, 500bp, and 600bp) indicating genetic variation within and among different herds of the cattle. Moreover,
results of this study showed that the spa (spa-X) gene present in coagulase positive (179) and coagulase negative (4) S. aureus
isolates. S. aureus isolates were fully sensitive (88%) to amoxicillin, followed by enrofloxacin (78%) and highly resistant to
penicillin (65%) and cephradine (100%). It is therefore concluded that S. aureus isolates were genetically different in the study
areas and amoxicillin is the drug of choice for treating subclinical mastitis
