H₂O₂ sensitivity of MVF-84 (wild-type S. aureus subsp. anaerobius) (●), RDKA84 (catalase-positive mutant of MVF-84) (○) and four strains of S. aureus isolated from clinical cases of mastitis (MN-42 (■), MN-45 (□), MN-73 (♦) and DGA-1 (◊)). These strains were exposed to various concentrations of H₂O₂. Each point represents the mean (± S.D.) of three experiments. Each experiment was performed in triplicate. Error bars indicate confidence level (95%); p values were determined using the Student’s t-test.