摘要
China is one of the countries with the highest prevalence of fluoroquinolone-resistant (FQr) Mycobacterium tuberculosis. Nevertheless, knowledge on the molecular characterization of the FQr M. tuberculosis strains of this region remains very limited. This study was performed to investigate the frequencies and types of mutations present in FQr M. tuberculosis clinical isolates collected in Shanghai, China. A total of 206 FQr M. tuberculosis strains and 21 ofloxacin-sensitive (FQs) M. tuberculosis strains were isolated from patients with pulmonary tuberculosis in Shanghai. The phenotypic drug susceptibilities were determined by the proportion method, and the mutations inside quinolone resistance-determining region (QRDR) of gyrA and gyrB genes were identified by DNA sequence analyses. Among 206 FQr M. tuberculosis strains, 44%(90/206) were multidrug-resistant isolates and 39%(81/206) were extensively drug-resistant isolates. Only 9%(19/206) were monoresistant to ofloxacin. In total, 79.1%(163/206) of FQr isolates harboured mutations in either gyrA or gyrB QRDR. Mutations in gyrA QRDR were found in 75.7%(156/206) of FQr clinical isolates. Among those gyrA mutants, a majority (75.6%) harboured mutations at amino acid position 94, with D94G being the most frequent amino acid substitution. Mutations in gyrA QRDR showed 100%positive predictive value for FQr M. tuberculosis in China. Mutations in gyrB were observed in 15.5%(32/206) of FQr clinical isolates. Ten novel mutations were identified in gyrB. However, most of them also harboured mutations in gyrA, limiting their contribution to FQr resistance in M. tuberculosis. Our findings indicated that, similar to other geographic regions, mutations in gyrA were shown to be the major mechanism of FQr resistance in M. tuberculosis isolates. The mutations in gyrA QRDR can be a good molecular surrogate marker for detecting FQr M. tuberculosis in China.