Occurrence of Staphylococcus aureus in milk and antibacterial properties of some herbal extracts on milk and hospital-acquired strains

Abstract

Staphylococcus aureus is a remarkable infectious agent, and with the development of antibiotic resistance by S. aureus, finding new, effective, and safe alternative therapeutic options in animals and humans is crucially demanded. In this study, the occurrence of S. aureus was explored by collecting nonmastitis bovine milk samples first, and then the effects of herbal extracts on methicillinresistant S. aureus (MRSA) strains isolated from cow's milk and humans in the hospitals were investigated. The occurrences of S. aureus in bovine raw milk samples were 13.4%. All raw milk S. aureus isolates were fully susceptible to cefoxitin, ceftiofur, penicillin G, and enrofloxacin. However, resistance was recorded for methicillin, streptomycin, tylosin, and sulfamethoxazole-trimethoprim. The most antibacterial resistance was recorded for oxytetracycline with 40% (intermediate resistance) and 15% (full resistance) respectively. The hospital-acquired S. aureus isolates were entirely resistant to methicillin and penicillin and were susceptible to some antibiotics. Sulfamethoxazole-trimethoprim was the most effective antibiotic with 83.4%. The antimicrobial activities of five medicinal herbs against raw milk S. aureus and hospital-acquired S. aureus isolates were assessed with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The findings affirmed that Rosmarinus officinalis and Nigella sativa acted as potent antibacterial agents on S. aureus strain obtained for nonmastitis bovine raw milk and hospital-acquired MRSA strains. The efficiency of these herbs against S. aureus isolates indicates their applicability as an antibacterial agent for alternative therapy in dairy products and human health and provokes further investigations in this area.