Abstract: ObjectiveTo investigating the cross resistance of moxifloxacin and levofloxacin in M. tuberculosis, gene mutations of quinolone-resistant isolates to provide a theoretical basis for clinical treatment. MethodsM. tuberculosis strain H₃₇Rv and 78 multidrug-resistant M. tuberculosis clinical isolates (73 LVF-resistant and 5 LVF-sensitive) were studied. The MICs of these isolates to moxifloxacin and levofloxacin were determined by the tube doubling dilution method on 7H9 media. The quinolone resistance-determining region (QRDR) mutations of gyrA genes from M. tuberculosis isolates were detected with DNA sequencing. ResultsThe MICs of MXF were lower 4 to 8 fold than that of LVF. The strain H₃₇Rv wasn’t found any gyrA gene mutation. 78 MDR-TB isolates have Ser95Thr gyrA mutations. Of 73 MDR-TB isolates with LVF resistance, 35（47.94%）were low-resistant to LVF （MICs 1 to 8μg/ml）, 31 （42.46%）were high-resistant to LVF. Four isolates have only gyrA Ser95Thr mutation, the other isolates had combinative gene mutations as follow: Ala90Val, Asp94His, Asp94Asn, Asp94Gly, Asp94Ala, and Asp94Tyr. ConclusionsThe MXF and LVF presented a incomplete cross-resistance. The mutation of gyrA gene correlates with the LVF and MXF resistances in M. tuberculosis.

Key words: Mycobacterium tuberculosis, Drug resistance,multiple,bacterial, moxifloxacin, Ofloxacin