Characterization of Staphylococcus aureus of cattle mastitis origin for two virulence-associated genes (coa and spa)

Bovine mastitis caused by Staphylococcus aureus is a worldwide disease of high economic significance. These organisms possess many virulence factors allowing them to evade host immune system. In the present study, 28 S. aureus isolates from milk obtained from Holstein–Friesian (H-F) crossbred and Rathi (a native breed) cattle with clinical mastitis were characterized for their two virulence-associated genes: coa and spa. All the isolates were confirmed genotypically by 23S rRNA ribotyping in which a species specific amplicon of 1,250 bp was obtained. Polymorphism was recorded in coa and spa genes. The coa gene produced one amplicon in each isolate either of 510, 600, 710 or 850 bp size with more variability observed in the Rathi isolates. The AluI restriction endonuclease generated three and five RFLP patterns with isolates from H-F crossbred and Rathi cattle, respectively. The RFLP patterns obtained from similar amplicons in isolates from two breeds did not differ. PCR amplification of the X-region for spa gene yielded amplicons of seven different sizes: 206, 243, 262, 277, 292, 306 and 339 bp with calculated number of 7, 8, 9, 10, 10, 11 and 12 bp repeats, respectively indicating presence of highly pathogenic strains. Among all the spa types, four were common to both animal groups, one was unique to H-F crossbred cattle and two were unique to Rathi cattle.