Characterization of variables that may influence ozenoxacin in susceptibility testing, including MIC and MBC values

Ozenoxacin is a new des-fluoro-(6)-quinolone active against pathogens involved in skin and skin structure infections, including Gram-positives resistant to fluoroquinolones. The in vitro bacteriostatic and bactericidal activity of ozenoxacin, ciprofloxacin, and levofloxacin was studied against 40 clinical isolates and 16 ATCC quality control strains under different test conditions, including cation supplementation, pH, inoculum size, inoculum preparation, incubation time, human serum, and CO2 incubation. The activity of ozenoxacin was unaffected by cation test medium supplementation, inoculum preparation, incubation time, and the increasing CO2 environment. On the contrary, ozenoxacin activity decreased by high inoculum (107 CFU/mL), increased presence of human serum in the medium, and increased pH. The last effect was different for ciprofloxacin and levofloxacin, which decreased activity when pH decreased. The bactericidal mode of action of ozenoxacin and control drugs was consistently maintained (MBC/MIC ratios ≤4) in spite of variations of their activity under different test conditions.