In vitro potency of moxifloxacin, clinafloxacin and sitafloxacin against 248 genetically defined clinical isolates of Staphylococcus aureus

The in vitro potency of three newer fluoroquinolones, moxifloxacin, clinafl oxacin and sitafloxacin was tested against 248 genetically defined Staphylo coccus aureus isolates, comprising 116 unrelated S. aureus, seven heterogen eous intermediate vancomycin-resistant S. aureus strains as well as 125 clo nally related methicillin-resistant S. aureus. All strains were susceptible to clinafloxacin and sitafloxacin based on an investigational breakpoint o f 1 mg/L and were less influenced by mutations within the grl and gyr gene loci. in one-quarter to one-third of the strains tested, reserpine decrease d slightly the MICs of moxifloxacin, clinafloxacin and sitafloxacin. Compar ed with moxifloxacin, clinafloxacin and sitafloxacin showed a significantly increased anti-staphylococcal potency.