Staphylococcus aureus is a major bovine mastitis pathogen responsible for heavy economic losses in dairy industry. Identification of epidemiological aspects associated with bovine mastitis may be helpful in treatment and management decisions. Due to high concern of zoonotic infections, we describe here, the distribution and antimicrobial susceptibility patterns of S. aureus from both cows with mastitis and nasal carriage of workers in contact to animals. Up to 38% workers were nasal carriers. Besides, S. aureus was isolated among 74% dairy herds suffering from mastitis, within 29.8% of mastitic quarter-milk samples. The isolates were tested for antimicrobial resistance, gyr, mecA, mecC and agr alleles. The gene gyr was detected in all S. aureus strains, 91 (77.7%) belonged to agr specificity group I, 11.9% affiliated to group II, 10 (8.5%) were agrIII, and 1.7% human derived isolates to the group IV. agr I was dominant in both human and animal isolates with 60 and 91%, respectively. Four human isolates harbored mecA gene, while no mecA or mecC genes were found in bovine derived isolates. Overall, 92% human isolates and 86.5% of cows’ derived strains were resistant to penicillin G. The resistance against non beta-lactam antibiotics was considerably greater in human than cows’ derived isolates, while different patterns of resistance share the same ecological niches. The high association of penicillin resistance to S. aureus in bovine mastitis highlights periodic surveillance of antibiotic resistance in livestock.

Key words: agr, Drug resistance, Livestock workers, Mastitis, S. aureus