Molecular characterisation of extensively drug-resistant Mycobacterium tuberculosis isolates in China

• Drug resistance mutations and genotypes of extensively drug-resistant tuberculosis (XDR-TB) isolates in China were analysed.
• DNA sequencing had a good sensitivity and specificity for diagnosing XDR-TB.
• The most prevalent genotype among XDR-TB in China was Beijing family.
• Beijing genotype showed no association with resistance-conferring mutations.
• Some mutations exhibited statistical associations with the Beijing family sublineage.

The emergence of extensively drug-resistant tuberculosis (XDR-TB) in China is a great threat to TB control. To determine the molecular characterisation of XDR-TB isolates from China and the correlations between specific drug resistance-associated mutations and different genotype strains, 58 XDR-TB isolates were sequenced in eight drug loci, including katG, inhA, oxyR–ahpC intergenic region, rpoB, eis, rrs, gyrA and gyrB, and were genotyped using spoligotyping and analysis of the noise transfer function region. Compared with the phenotypic data, the sensitivities and specificities for DNA sequencing were 87.9% and 100.0% for isoniazid (INH), 91.4% and 98.3% for rifampicin (RIF), 60.4% and 100.0% for kanamycin (KAN) and 81.0% and 100.0% for ofloxacin (OFX), respectively. A combination of eight drug loci predicted XDR-TB phenotypes with 53.4% sensitivity (31/58 isolates) and 100.0% specificity. The most frequent mutations among these XDR-TB isolates were katG315 and inhA-15 (for INH), 531, 526 and 516 in rpoB (for RIF), rrs1401 and eis–10 (for KAN) and 94, 90 and 91 in gyrA (for OFX). Also, among these XDR-TB isolates, 44 (75.9%) were identified as Beijing genotype strain, of which 31 (70.5%) belonged to the modern Beijing sublineage. inhA-8, rpoB526 and rpoB531 mutations demonstrated significant statistical associations with ancient and modern Beijing family sublineage (P < 0.05). However, Beijing and non-Beijing genotypes showed no association with specific resistance-conferring mutations. These results will be helpful in designing new molecular biology-based techniques to diagnose XDR-TB in China.