In vitro antistaphylococcal activities of two investigative fluoroquinolones, CI-960 and WIN 57273, compared with those of ciprofloxacin, mupirocin (pseudomonic acid), and peptide-class antimicrobial agents.

By using broth microdilution, 373 clinical isolates of staphylococci were studied to determine their susceptibilities to CI-960, WIN 57273, ciprofloxacin, mupirocin, vancomycin, teicoplanin, and ramoplanin. Test strains comprised 179 strains of Staphylococcus aureus and 194 strains of coagulase-negative species. Strains of S. aureus were susceptible to CI-960, which had a mode MIC of 0.032 micrograms/ml and an MIC for 90% of the strains of 2 micrograms/ml. CI-960 was equally active against methicillin-susceptible and -resistant S. aureus strains as well as ciprofloxacin-resistant strains. Similarly, WIN 57273 was highly active, with a mode MIC of 0.008 micrograms/ml and an MIC for 90% of the strains of 1 micrograms/ml. No cross-resistance to CI-960 and WIN 57273 among ciprofloxacin-resistant strains was detected. Mupirocin was four- to eightfold more active than ramoplanin, vancomycin, and teicoplanin. With regard to coagulase-negative staphylococci, CI-960 and WIN 57273 were the most active of the test compounds, inhibiting all strains at 0.5 and 1 micrograms/ml, respectively. Against the same strains, mupirocin was fourfold more active than ramoplanin and eightfold more active than vancomycin. Five strains of S. haemolyticus were found to be resistant to ciprofloxacin, while resistance to teicoplanin was found among strains of S. epidermidis, S. haemolyticus, S. hominis, S. saprophyticus, S. simulans, S. warneri, and S. xylosus.