MIC andgyrA/Bgenetic analyses of fluoroquinolones againstmycobacterium tuberculosisisolated in Japan

Abstract

Background: The certain alteration of DNA gyrase causes fluoroquinolone resistances to Mycobacterium tuberculosis (Mtb). The aim of this study was to evaluate the interrelations of minimum inhibitory concentrations (MICs) of Sitafloxacin (STFX), Moxifloxacin (MFLX), Levofloxacin (LVFX) and Ciprofloxacin (CPFX), and the mutations in the gyrA/B genes in Mtb. Methods: A total of 109 clinical Mtb isolates including 73 multi-drug resistant (MDR) strains were subjected to measure the MICsusing OADC contained Middlebrook 7H9. Direct DNA sequencing of quinolone resistance-determining regions (QRDRs) were performed. Results: MIC 50 and MIC 90 of STFX, MFLX, LVFX and CPFX were 0.06µg/ml, 0.25µg/ml, 0.5µg/ml, 0.5µg/ml, and 1µg/ml, 4µg/ml, 8µg/ml, 8µg/ml, respectively. Eight (7%) and 37 (34%) strains had mutations in gyrB and gyrA The mutant patterns were D94G, D94A, A90V, D94H, D94N and G88A in gyrA , and A543V, A543T, E540D, R485C, D500A, I552S and D577A in gyrB . The MICs were significantly higher in the gyrA mutants compared to wild types (p gyrA mutants were 2µg/ml (1.0–4.0 µg/ml) and 0.5 µg/ml (0.25–1.0 µg/ml). The proposed epidemiological cut-off (ECOFF) value of STFX was 0.125µg/ml. With this ECOFF, 3% strains were susceptible to STFX among LVFX resistant strains defined as MIC≥2 µg/ml. Four isolates of gyrB mutants showed relatively low MICs. Discussion: and Conclusion: STFX showed the lowest MIC 50 , MIC 90, and a relatively low ECOFF, indicated that STFX might be more effective in MDR or in gyrA mutant stains. Mutation of gyrA had an obvious relevance to FQ resistance, whereas the relevance of gyrB remained obscure in our study.