DNA gyrase of Staphylococcus aureus and inhibitory effect of quinolones on its activity

DNA gyrase from Staphylococcus aureus FDA 209P was partially purified by lysostaphin treatment, saturation with ammonium sulfate, and affinity chromatography on heparin-Sepharose and with a concentrator (Centricon 30). It was found to consist of two subunits: alpha and beta. The ability of new quinolone antibacterial agents such as norfloxacin, ofloxacin, and ciprofloxacin to inhibit DNA gyrase activity and cell growth was investigated. The inhibitory effects of the new quinolones against the activity of S. aureus DNA gyrase were in parallel with their antibacterial activities. The 50% inhibitory doses of norfloxacin, ofloxacin, and ciplofloxacin were 0.34, 0.31, and 0.24 micrograms/ml, respectively, while the 50% inhibitory doses of nalidixic acid and cinoxacin, which were less active against S. aureus FDA 209P, were 100 micrograms/ml or more.