Comparative in vitro activity of CI934, a new fluoroquinolone, alone and in combination with coumermycin, against gram-positive bacteria.

The in vitro activity of Cl934, a new quinolone antimicrobial agent, was studied against 314 strains of Gram-positive bacteria representing 6 genera: Staphylococcus aureus, Streptococcus faecalis, S. agalactiae, S. pyogenes, S. pneumoniae, S. milleri, viridans streptococci, Listeria monocytogenes, Corynebacterium JK, Mycobacterium fortuitum and Bacillus spp.; and compared with that of enoxacin, ciprofloxacin, penicillin G, ampicillin, coumermycin, oxacillin, vancomycin, teicoplanin, rifampin, rifapentine, LM 427, erythromycin, minocycline, tetracycline and clindamycin. The agar dilution method was used. Cl934 was very active in vitro, with MIC90 less than or equal to 0.5 mg/l against most species tested, except for S. faecalis and M. fortuitum. It was usually 2 to 8-fold more active than ciprofloxacin. Cl934 was also tested by the killing curve method, alone and in combination with coumermycin. It was rapidly bactericidal against most species tested, including S. faecalis. A synergistic interaction was observed with coumermycin against S. aureus, S. agalactiae, S. milleri and S. faecalis. The only antagonistic interaction occurred against L. monocytogenes exposed to 8 X MIC of Cl934 with 2 X MIC of coumermycin.