Distribution of pathogenic factors in Staphylococcus aureus strains isolated from intra-mammary infections in cattle and buffaloes

Staphylococcus aureus has been reported as a major pathogen in dairy animals. The pathogenic potential of S. aureus isolates is attributed to a combination of extracellular factors and invasive properties that are controlled at the genomic level. In order to elucidate patterns of pathogenic genes, 346 isolates of S. aureus were recovered from Sahiwal, Karan Fries (cattles) and Murrah (buffalo) suffering from intra-mammary infection. The distribution of pathogenic genetic-determinants of isolates was evaluated using the PCR assays. All the isolates showed variations and variable number of repeats (3-12) in Spa gene. The number of repeats was the highest in Sahiwal isolates, followed by Karan Fries and Murrah. All the tested isolates were positive for genetic determinants of Spa, Ebp, Eno and FnbA. The prevalence of other pathogenic genes, namely, Fib, FnbB, Bbp and Map was more in isolates from Sahiwal as compared to isolates from Karan Fries and Murrah. A significant number of isolates (82%) showed presence of capsular gene subtypes (5 & 8). The toxin genes, namely, Sec, See, Seg and Sei were common in all the breeds; however, their proportion was less. Seb and Sed were present in only cattle originated isolates of S. aureus. Isolates of both cattle breeds (Sahiwal and Karan Fries) showed similar patterns of pathogenic factors that could be due to commonness or dissemination of strains among these animals. Conversely, variations in expression of pathogenicity factors in isolates of cattle and buffaloes were observed. Overall, the isolates from Murrah were less virulent and consisted of less proportion of pathogenic factors. However, the comparative observation suggested that a limited number of pathogenic factors of S. aureus seemed to be crucial in mastitis in various animals.