Antistaphylococcal Activity of CG400549, a New Experimental FabI Inhibitor, Compared with That of Other Agents

Among 203 strains of Staphylococcus aureus, the MICs of CG400549 were 0.06 to 1.0 microg/ml, with MIC(50) and MIC(90) values of 0.25 microg/ml each. All strains were susceptible to linezolid and quinupristin-dalfopristin (MICs, 0.25 to 2.0 microg/ml). The daptomycin MICs were 0.25 to 2.0 microg/ml for methicillin-susceptible and 0.25 to 4.0 microg/ml against methicillin-resistant strains (including vancomycin-intermediate strains). Single-passage selection testing showed low resistance frequencies with CG400549, but multistep analysis showed that CG400549 yielded resistant mutants after 14 to 17 days in all strains tested.