Characterization of hemolytic activity of Staphylococcus aureus strains isolated from bovine mastitic milk

Beta (beta) and delta (delta)-hemolysin of Staphylococcus aureus strains were cultured in vitro in milk lactoserum (whey) prepared from both healthy and mastitis bovine milk. Production of beta- and delta-hemolysins were detected in 12 out of 50 strains studied. The association between N-acetyl-beta-D-glucosaminidase (NAGase) activity, plasmin activity (PL) and trypsin inhibitory capacity (TIC), known as inflammatory indicators for mastitis, and hemolytic activity were also studied. Mastitic milk decreased directly the lytic effect of both beta-and delta-hemolysins of S. aureus on hemolytical blood agar plates. S. aureus in healthy milk samples produced more beta-hemolysin (3 times) and delta-hemolysin (2 times) when compared to S. aureus supernatants in milk from infected quarters. Furthermore, beta- and delta-hemolysis correlated negatively with TIC and NAGase and PL activities. Addition of reduced glutathione (GSH) or beta-mercaptoethanol into the artificial medium enhanced hemolysins activity.