Selected Mutations by Nemonoxacin and Fluoroquinolone Exposure Among Relevant Gram-Positive Bacterial Strains in Taiwan.

Nemonoxacin is a nonfluorinated quinolone with good bactericidal effects against quinolone-resistant Gram-positive microorganisms. The in vitro inducible resistance of nemonoxacin against clinically relevant Gram-positive pathogens was compared with ciprofloxacin, levofloxacin, and moxifloxacin. Three strains of each bacterial species, including Streptococcus pneumoniae, Staphylococcus aureus, Enterococcus faecium, and Enterococcus faecalis, were cultured. All clinical isolates had wild-type gyrA, gyrB and parC, parE before further in vitro test. DNA sequencing for the quinolone resistance determination region (QRDR) of gyrase and topoisomerase genes was performed. Nemonoxacin had the lowest minimum inhibitory concentrations (MICs) among all quinolones. During exposure to nemonoxacin, the MIC values did not increase for S. aureus, E. faecium, and E. faecalis, and revealed fourfold increase of S. pneumoniae over three cycles of a stepwise resistance selection. DNA sequencing did not show inducible QRDR resistance of nemonoxacin group. Compared to other fluoroquinolones, nemonoxacin has a low potential for inducing resistant pathogens.