Determination of phenotypical and genotypical characterization and antimicrobial resistance genes of staphylococcus aureus isolated from milk of dairy cows with mastitis

Aim: Mastitis is one of the most common diseases of dairy cattle and causes significant economic losses. Staphylococcus aureus produces many virulence factors that facilitate the adhesion and penetration of damaged tissues, and thereby, cause subclinical mastitis. This study was aimed at investigating the phenotypic and genotypic characteristics and antimicrobial susceptibility of S. aureus.. Materials and Methods: A total of 241 S. aureus strains isolated from bovine mastitis cases were tested phenotypically (catalase, coagulase, haemolysis, DNase, mannitol fermentation and biofilm formation) and genotypically (by the polymerase chain reaction (PCR) technique). Antimicrobial susceptibility was tested using 15 different antibiotics. Results: While the isolates showed different levels of haemolytic activity (? 47%, ? 42%, ? 10% and ? 1%), only the ?-haemolytic strains produced a positive CAMP-like reaction. Although all isolates were able to grow on MSA containing 7.5% NaCl, mannitol fermentation activity was observed in 80.5% of the isolates. The nuc gene was detected in all isolates, but only 84.2% of the isolates showed DNase activity. The Congo red agar method can be used to detect the biofilm forming capability of isolates, but the crystal violet staining method gives more reliable results. The sec gene was the most common enterotoxin genes (84%). Three isolates harboured the mecA gene, but were sensitive to methicillin. Conclusion: Phenotypic variations among isolates result in the misclassification of S. aureus strains and require the use of molecular methods. The rapid and accurate molecular typing of S. aureus can aid in both determining the prevalence of this infectious microorganism and preventing epidemic infections.