Characterization of multiple and extensively drug resistant Mycobacterium tuberculosis isolates with different ofloxacin-resistance levels.

The goal of the study was to determine different mutation types in gyrA and gyrB genes in Mycobacterium tuberculosis strains with low-level (2 μg/ml) and high-level (10 μg/ml) ofloxacin (OFL) resistance and to compare genetic diversity of ofloxacin-resistant and susceptible M. tuberculosis isolates. M. tuberculosis isolates were collected in Leningrad Region in 2011. DNA sequencing showed that 54.3% of isolates with low-level and 76.9% of isolates with high-level OFL-resistance had mutations in gyrA gene. Few isolates carried mutations in gyrB gene - five among isolates with low-level resistance and two among high-level resistant isolates. Altogether, detection of point mutations in both DNA gyrase genes allows to identify 66.9% of mycobacterial isolates with low-level and 84.5% of isolates with high-level of OFL-resistance. Novel mutations S91L in gyrA gene and S512L in gyrB gene described in this study were detected in OFL-resistant isolates and may play role in M. tuberculosis fluoroquinolone resistance. M. tuberculosis Beijing family spoligotypes were identified among 70.8% of isolates with low-level resistance, 84.6% of isolates with high-level resistance and 50% of strains susceptible to all tuberculosis drugs. Fisher's exact test revealed significant difference between Beijing prevalence in groups of drug-susceptible or high-level OFL-resistant M. tuberculosis strains (p-value = 0.032).