Molecular Identification, Biofilm Formation Ability and Antimicrobial Resistance of Staphylococcus warneri Isolates Obtained from Mastitic Cows in the Aegean Region

Staphylococcus warneri is a species belonging to the coagulase-negative staphylococci (CoNS) group and is commonly found as a commensal organism on the skin and mucosal surfaces of humans and animals. In recent years, the increasing isolation rates of CoNS from milk and dairy products have highlighted their significance in terms of both food safety and livestock production. This study aimed to confirm S. warneri isolates obtained from milk samples using molecular methods, to evaluate their biofilm-forming ability through the Congo Red Agar (CRA) method, and to determine their phenotypic antimicrobial resistance profiles. For this purpose, 650 milk samples were examined, the presence of S. warneri was investigated using phenotypic identification methods, and suspected isolates were confirmed by Polymerase Chain Reaction (PCR). The biofilm-forming ability of isolates identified as S. warneri was assessed on CRA medium. In addition, the susceptibility of the isolates to eight different antibiotics was determined by the Kirby-Bauer disk diffusion method according to CLSI standards. Among the 650 samples analyzed, 21 isolates were found to be positive for S. warneri, and all isolates demonstrated biofilm-forming capacity. According to the antibiotic susceptibility results, the isolates exhibited resistance to oxacillin (90.5%), trimethoprim–sulfamethoxazole (81.0%), penicillin (47.6%), tetracycline (38.1%), chloramphenicol (23.8%), erythromycin (14.3%), and doxycycline (14.3%), while all isolates were fully susceptible to gentamicin (100%). In conclusion, the presence of S. warneri, a CoNS species, in dairy cattle within the sampling region was confirmed; their biofilm-forming abilities were determined; and the most appropriate antibiotic options for treatment were evaluated phenotypically based on resistance profiles.