Activity of moxifloxacin in combination with vancomycin or teicoplanin against Staphylococcus aureus isolated from device-associated infections unresponsive to glycopeptide therapy.

We tested the in vitro bactericidal activity of moxifloxacin, a new 8-methoxyquinolone, alone and in combination with vancomycin or teicoplanin at different multiples of minimum inhibitory concentration (MIC) against 8 methicillin-ciprofloxacin-resistant Staphylococcus aureus (M-C-RSA) and 1 methicillin-ciprofloxacin susceptible S. aureus (M-C-SSA) recently isolated from device-associated infections unresponsive to or relapsing after glycopeptide therapy, despite device removal. MICs of vancomycin ranged from 1 to 4 microg/ml, MICs of teicoplanin ranged from 2 to 8 microg/ml; MICs of moxifloxacin were always 2 microg/ml against M-C-RSA isolates and 0.125 microg/ml against the M-C-SSA isolate. The 9 strains resulted tolerant when tested for vancomycin, teicoplanin, and moxifloxacin used alone at 2 x MIC. In all cases the combination of moxifloxacin and teicoplanin or vancomycin appeared to be bactericidal already at MIC concentration for glycopeptides plus 0.5 x MIC concentration for moxifloxacin. If these results are confirmed in vivo in animal experiments, the combination of moxifloxacin with glycopeptides might be useful for treating device-associated infections, and in preventing the frightening phenomenon of increasing MICs for glycopeptides.