Some Studies on Phenotypic and Genotypic Characters of Small Colony Variants Staphylococcus aureus Isolated from Dairy Cows Infected with Mastitis in Egypt

In veterinary medicine, the small colony variants (SCVs) S.aureus was ignored, but recently the interest in its analysis has been increased because it causes chronic infections with difficulty in laboratory isolation and identification. Therefore, this study aimed to investigate the phenotypic and genotypic characteristics of S. aureus SCVs and their mastitis prevalence in dairy cows, as well as the protein profile discrepancy between parent strains of S.aureus and S.aureus SCVs. A total number of 130 milk samples were collected and examined from commercial Friesian-Holstein dairy herds in Egypt. Of the examined milk samples chronic subclinical mastitic milk samples constituted 58.46%, while clinical mastitis milk samples were 9.23%. S.aureus SCVs were only isolated from chronic subclinical samples with percentage of 23.68%. In order to distinguish between S.aureus parent strains and S.aureus SCVs, Phenotypic characters such as, growth rate, colony size, Mannitol fermentation, hemolysis, rabbit plasma coagulation and catalase test were examined. In addition the isolated Staphylococcus species were investigated using Polymerase Chain Reaction (PCR) technique to approve the isolation of SCVs S. aureus. In addition protein profile between parent strains of S.aureus and SCVs have been tested and evaluated. The results showed the significance of SCVs S.aureus in herd health, as a result of difficulty of its diagnosis, the percentage of SCVs infection may be increased, so more attention should be paid for the investigation of observed colony morphologies. Isolates of SCVs S.aureus should be subjected to antimicrobial susceptibility testing with a protocol for treatment as they showed higher resistance against many antibiotics when compared with parent strains of S.aureus; this study suggests that Ciprofloxacin, Enrofloxacin and rifampin can be used for treatment of SCVs S.aureus.