WCK 771 demonstrated MIC(50) and MIC(90)s of 0.03 and 1 microg/ml, respectively, against 297 recent U.S. community-acquired and hospital strains of Staphylococcus aureus, irrespective of quinolone or glycopeptide resistance. Against quinolone-resistant strains, MIC(90)s of WCK 771 and moxifloxacin were 1 and 16 microg/ml, respectively.