Multicenter study in Taiwan of the in vitro activities of nemonoxacin, tigecycline, doripenem, and other antimicrobial agents against clinical isolates of various Nocardia species.

Abstract

The aim of this study was to assess the in vitro activities of nemonoxacin (a novel nonfluorinated quinolone), doripenem, tigecycline, and 16 other antimicrobial agents against Nocardia species. The MICs of the 19 agents against 151 clinical isolates of Nocardia species were determined by the broth microdilution method. The isolates were identified to the species level using 16S rRNA gene sequencing analysis. The results showed that N. brasiliensis (n=60; 40%) was the most common species, followed by N. cyriacigeorgica (n=24; 16%), N. farcinica (n=12; 8%), N. beijingensis (n=9), N. otitidiscaviarum (n=8), N. nova (n=8), N. asiatica (n=7), N. puris (n=6), N. flavorosea (n=5), N. abscessus (n=3), N. carnea (2), and one each of N. alba, N. asteroides complex, N. rhamnosiphila, N. elegans, N. jinanensis, N. takedensis, and N. transvalensis. The MIC90s of the tested quinolones against the N. brasiliensis isolates were in the order nemonoxacin=gemifloxacin<moxifloxacin<levofloxacin=ciprofloxacin, and the MIC90s of the tested carbapenems were in the order doripenem=meropenem<ertapenem<imipenem. Tigecycline had a lower MIC90 (1 μg/ml) than linezolid (8 μg/ml). The MIC90s of the tested quinolones against N. cyriacigeorgica isolates were in the order nemonoxacin<gemifloxacin<moxifloxacin<levofloxacin<ciprofloxacin, and the MIC90s of the tested carbapenems were in the order imipenem<doripenem=meropenem<ertapenem. Nemonoxacin had the lowest MIC90 values among the tested quinolones against the other 17 Nocardia isolates. Among the four tested carbapenems, imipenem had the lowest MIC90s. All of the clinical isolates of N. beijingensis, N. otitidiscaviarum, N. nova, and N. puris and more than half of the N. brasiliensis and N. cyriacigeorgica isolates were resistant to at least one antimicrobial agent. The results of this in vitro study suggest that nemonoxacin, linezolid, and tigecycline are promising treatment options for nocardiosis. Further investigation of their clinical role is warranted.