Prevalence and molecular characterization of fluoroquinolone-resistant Mycobacterium tuberculosis isolates in China.

China is one of the countries with the highest burdens of multidrug-resistant (MDR) and fluoroquinolone (FQ)-resistant tuberculosis (TB) globally. Nevertheless, knowledge about the prevalence and molecular characterization of FQ-resistant Mycobacterium tuberculosis isolates from this region remains scant. In this study, 138 M. tuberculosis isolates determined by the agar proportion susceptibility method to be resistant to ofloxacin (OFX) were enrolled from a national drug resistance survey of China. All these strains were tested for susceptibility to ofloxacin, levofloxacin, moxifloxacin, gatifloxacin, and sparfloxacin using liquid Middlebrook 7H9 medium. The entire gyrA and gyrB genes conferring FQ resistance were sequenced, and spoligotyping was performed to distinguish different genotypes. Overall, the prevalence of resistance in China was highest for ofloxacin (3.76%), intermediate for levofloxacin (3.18%) and moxifloxacin (3.12%), and lowest for sparfloxacin (1.91%) and gatifloxacin (1.33%). Mutations in the gyrA gene were observed in 89 (64.5%) out of the 138 OFX-resistant M. tuberculosis strains. Positions 94 and 90 were the most frequent sites of mutation conferring FQ resistance on these strains, accounting for high-level FQ resistance. Furthermore, the Beijing genotype showed no association with high-level FQ resistance or distribution in hot spots in the quinolone resistance-determining region (QRDR) of gyrA. Our findings provide essential implications for the feasibility of genotypic tests relying on detection of mutations in the QRDR of gyrA and the shorter first-line treatment regimens based on FQs in China.