Virulence and antimicrobial resistance gene profiles of Staphylococcus aureus associated with clinical mastitis in cattle

Staphylococcus aureus (S. aureus) is the most prevalent microorganism associated with mastitis in cattle, which harbours several virulence factors and antibiotic resistance genes. The present study aimed to characterize S. aureus isolated from mastitic milk of the cattle for antibiotic resistance (blaZ and mecA), haemolysins (hla and hlb) and enterotoxins (sea, seb, sec, and sed) genes. A total of 69 staphylococci were isolated and phenotypically characterized for haemolytic properties on 5% sheep blood agar medium. Out of 69 isolates, 55 (79.71%) were identified as S. aureus by polymerase chain reaction assay. Among S. aureus, the majority of the isolates harboured the gene blaZ (92.73%), followed by coa (89.09%), hlb (60%) and hla (49.09%). Gene mecA responsible for methicillin resistance was detected in 23.64% of S. aureus isolates. Enterotoxin genes seb (9.09%), sec (1.82%) and sed (7.27%) responsible for food poisoning were detected at a comparatively lower rate and none of the S. aureus strain was found positive for sea. Additionally, antimicrobial susceptibility study of S. aureus against 18 antimicrobial discs showed maximum resistance to oxytetracycline, penicillin, and fluoroquinolone groups, contrarily, we observed maximum sensitivity to methicillin and cefuroxime antimicrobials. The high occurrence rate of S. aureus harbouring genes for virulence factors and antimicrobial resistance needs appropriate strategies to control the pathogen spread to the human population.