Comparative in vitro activities of nemonoxacin, doripenem, tigecycline and 16 other antimicrobials against Nocardia brasiliensis, Nocardia asteroides and unusual Nocardia species

Objectives: The aim of this study was to assess the in vitro activities of nemonoxacin (a novel non-fluorinated quinolone), doripenem, tigecycline and 16 other antimicrobial agents against the Nocardia species. Methods: MICs of 19 antimicrobial agents for 125 clinical isolates of the Nocardia species were determined by the broth microdilution method. Results: Nocardia brasiliensis (n=61), Nocardia asteroides (n=45), Nocardia flavorosea (n=5), Nocardia otitidiscaviarum (n=4), Nocardia farcinica (n=3), Nocardia beijingensis (n=2), Nocardia puris (n=2) and one each of Nocardia nova, Nocardia jinanensis and Nocardia takedensis were identified based on a 16S rRNA gene sequencing analysis. For N. brasiliensis isolates, the MIC(90)s of the tested quinolones were in the order nemonoxacin<gemifloxacin=moxifloxacin<levofloxacin=ciprofloxacin, and the MIC(90)s of the tested carbapenems were in the order doripenem=meropenem<ertapenem<imipenem. Tigecycline had a lower MIC90 (1 mg/L) than linezolid (8 mg/L). For N. asteroides isolates, the MIC(90)s of the tested quinolones were in the order nemonoxacin<gemifloxacin=moxifloxacin<levofloxacin<ciprofloxacin, and the MIC(90)s of the tested carbapenems were in the order doripenem=meropenem=imipenem<ertapenem. For the other 19 Nocardia species isolates, nemonoxacin showed good activity with the lowest MIC90 of the tested quinolones. Among the four tested carbapenems, doripenem and meropenem had comparatively lower MIC(90)s. Conclusions: The results of this in vitro study suggest that nemonoxacin, linezolid and tigecycline show promise as treatment options for nocardiosis. Further investigation of their clinical role is warranted.