Comparative In Vitro Activities of Lysostaphin and Other Antistaphylococcal Antibiotics on Clinical Isolates of Staphylococcus aureus

The in vitro activity of lysostaphin against clinical isolates of Staphylococcus aureus was determined by conventional tube-dilution methods. For comparison, minimal inhibitory concentration (MIC) values were also determined for penicillin G, ampicillin, methicillin, ristocetin, vancomycin, and erythromycin. Phage type and penicillinase and coagulase production were determined for each isolate. The MIC values for lysostaphin ranged from <0.047 to 12.5 μg/ml; 96% of the penicillinase-positive strains were inhibited by 1.56 μg/ml of lysostaphin, whereas 3.12 μg/ml of vancomycin and methicillin were required to attain the same degree of inhibition.