Abstract: Objective To analyze the mutations of gyrase (gyr) gene in multidrug-resistant (MDR) M.tuberculosis clinical isolates, and to investigate the correlation between the gyr mutations and fluoroquinolone (FQ) resistance.  Methods Seventeen MDR M.tuberculosis isolates were analyzed the FQ resistance using minimum inhi-bitory concentration (MIC) method, and detected gyr mutations by DNA sequencing.  Results No mutation was observed in gyrA and gyrB genes of M.tuberculosis H37Rv, while 17 clinical MDR isolates all carried the substitution AGC→ACC at codon 95. Among 12 FQ-resistant isolates, 10 (83.3%) harbored missense mutation in gyrA gene, including codon 89, 90, 91 and 94. In addition, 1 isolate had mutation at codon 500 of gyrB gene. Among 9 moxifloxacin-resistant isolates, 8 (88.9%) showed the mutations in gyrA gene.  Conclusion The mutation in gyrA is one of the most important mechanism for FQ resistance in M. tuberculosis. The most frequent mutations located at codon 89, 90, 91 and 94.  

Key words: Drug resistance, multiple, bacterial, Mycobacterium tuberculosis, DNA gyrase, Fluoroquinolones, Mutation