Isolation and characterization of Staphylococcus aureus from bovine mastitis in Andhra Pradesh

Staphylococcus aureus is the key causative agent for contagious mastitis and responsible for subclinical infections leading to economic loss to dairy industry worldwide. Hence, the present work was planned to isolate and characterize the Staphylococcus aureus from bovine mastitis cases of S. aureus origin. From non therapeutic areas, a total of 381 staphylococcal isolates were recovered out of 438 milk samples with percentage positivity of 86.98, whereas, out of 60 milk samples in selected therapeutic areas 40 staphylococcal isolates with positivity of 66.67% were recovered based on cultural and biochemical tests. A total of 290 out of 381 and 30 out of 40 culturally positive isolates respectively from non therapeutic and therapeutic areas were confirmed as S. aureus by PCR method targeting the 16S rRNA with an expected amplicon size of 229bp. Sequencing and nucleotide analysis of 16S rRNA amplicons of non therapeutic area isolates showed 99.3% identity whereas therapeutic isolates showed 95-100% identity with gene bank reference strains. On phylogenetic analysis, isolates form non therapeutic area were not closely related to reference gene bank strains whereas isolates of therapeutic area were shown close evolutionary relationship with gene bank reference strains. Further, Peruru isolates of therapeutic area have shown close evolutionary relationship with Spain isolate KX348312.1 and formed separate group in cladogram.