Molecular characterization of isoniazid-resistant Mycobacterium tuberculosis isolates from Xi'an, China.

The increased prevalence of isoniazid (INH)-resistant tuberculosis (TB) has become a significant challenge for TB control in the last 10 years. It has been reported that INH resistance is most frequently associated with katG 315 and inhA-15 mutations. The relative significance of these mutations in INH-resistant Mycobacterium tuberculosis and their association with the different genotypes of M. tuberculosis in Xi'an, China, was investigated. Eighty-nine INH-resistant isolates were subjected to molecular characterization of hotspot mutations within katG 315 and inhA-15 by Multiplex allele-specific PCR, and results from 10 isolates were confirmed by direct sequencing. Mutations in katG 315 and inhA-15 were detected in 58 and 7 isolates, respectively. These isolates were genotyped by mycobacterial interspersed repetitive unit-variable number of tandem repeats and Spoligotyping. Spoligotyping showed that 79 isolates (89%) belonged to Beijing family. Mycobacterial interspersed repetitive unit-variable number of tandem repeats typing revealed significant differences in clustering level between Beijing and non-Beijing family (56% vs. 9%, p = 0.002), which indicated the active transmission of Beijing family in INH-resistant isolates. Our results suggested that the katG 315 mutants were predominant in INH-resistant isolates in Xi'an and the hotspot mutations within katG 315 and inhA-15 can be used as genetic markers for detection of INH resistance.