Phenotypic characteristics of Staphylococcus aureus isolated from bovine mastitis in Israeli dairy herds

A study of the characterization of the phenotypic patterns of Staphylococcu s aureus strains isolated from bovine subclinical mastitis in Israeli dairy herds and their correlation with the severity of the disease was undertake n. A total of 400 chronically S. aureus-infected Israeli-Holstein cows, fro m 15 dairy herds were included in this study. Based on the results of the b iochemical reactions, of the anti-biogram and phage typing, one major type of S. aureus was determined in each herd, its prevalence being between 54 a nd 100% of the total isolates from the same herd. The majority of the isola tes were found to be non-haemolytic (62.7%). The most common phage type was 3/A,3/C,55,71, which was predominant in five herds. In two herds none of t he isolates (24) were typable by this set of phages. All isolates were susc eptible to methicillin, erythromycin, cephalorin, norfloxacin, trimethoprin -sulphamethoxazole and novobiocin. Most isolates were resistant to penicill in (96.6%) and 52% to oxytetracyclin. Differences in protein patterns betwe en 50 and 36 kDa were found by one-dimensional sodium dodecyl sulphate-poly acrylamide gel electrophoresis. No correlation between any combination of t he phenotypic characteristics were found when correlation was done with mil k yield and somatic cell count, corresponding to the 6 months before sampli ng. Otherwise, a positive correlation was found between type of haemolysis and the N-acetyl-beta -glucosaminidase (NAGase) values. In milk from quarte rs infected with the non-haemolytic strains, the level of NAGase was signif icantly lower (P < 0.05) than that from quarters infected with the haemolyt ic strains (69.7 and 105.9, respectively). However, the level of NAGase act ivity in the milk of the quarters infected with the non-haemolytic strains was significantly higher (P < 0.05) when compared to the milk of quarters i nfected with coagulase negative staphylococci (43.5).