Mastitis remains the most frequent and the most expensive disease of dairy breeding. The objective of the study was to study S. aureus isolates collected from sub-clinical bovine mastitis in the Tiaret region, Algeria, by determining their antimicrobial susceptibility and their virulence traits. Sixty-two S. aureus isolates collected from subclinical bovine mastitis were studied by determining their antimicrobial susceptibility according to CLSI guidelines and nine genes encoding virulence factors and resistance to methicillin and penicillin were determined by PCR. Multi-drug resistance was observed in 19 (30.64%) isolates and five (8%) were methicillin-resistant S. aureus (MRSA), four of them harbored the mecA gene; however, mecC gene was not detected. Out of 59 penicillin resistant isolates, 14 harbored the blaZ gene; one of them co-harbored the mecA gene. The following virulence genes were detected: eta (n=23; 37%), icaA (20; 32.2%), icaD (18; 29%), etb (16; 25.8%), luk E-D (14; 22.5%), and sea (6; 9.6%). The tsst-1, lukF/lukS, luk-M genes were not detected. The occurrence of MRSA and multi-drug resistant (MDR) S. aureus isolates as well as genes encoding virulence factors playing an important role in the pathogenesis of sub-clinical bovine mastitis and of harmful potential to human is a cause for concern.

The aims of this work was to study the sensitivity of Staphylococcus aureus strains isolated from bovine mastitis antibiotics. A total of 22 pure strains of S. aureus were collected from 58 quarter milk samples from 29 (69,04%) dairy cows detected with subclinical mastitis by California mastitis test (CMT). The isolates were subjected to an antibiogram. The tests showed that one strain among the isolates tested is MRSA (Methicillin resistant Staphylococcus aureus). This MRSA exhibited cross-resistance to all betalactamines which extends to other families of antibiotics. SASM strains also showed strong resistance. vis-à-vis penicillin (95,23%) and tetracycline's (90,47%) Resistance was also recorded vis-à-vis; the combination amoxicillin + clavulanic acid (47,61%), erythromycin (19,04%), the combination trimethoprim + sulfamethoxazole (4,76%) and bacitracin (9.52%). neomycin, gentamicin, ciprofloxacin and clindamycin were active on MRSA's. The high prevalence of subclinical mastitis and multi-resistant S. aureus strains testifies to the need for an effective control strategy based essentially on the early detection of subclinical mastitis, the identification of the causative agent and the study of its sensitivity to common antibiotics.