Effects of mutations in multiple Ethionamide-resistance-associated genes among Mycobacterium tuberculosis clinical isolates from China.

OBJECTIVES

The growing burden of drug-resistant tuberculosis (TB) constitutes a major public health challenge. Ethionamide (ETH), a second-line anti-TB drug, plays an important role in the treatment of multidrug-resistant tuberculosis (MDR-TB). However, the molecular mechanisms underlying ETH resistance remain incompletely elucidated. Thus, this study aimed to evaluate the effects of mutations in ETH resistance-associated genes (inhA, ethA, ethR, and mshA) on ETH resistance levels among Mycobacterium tuberculosis (MTB) isolates from China.

METHODS

A total of 137 MTB isolates from China were tested for ETH minimum inhibitory concentrations (MICs) pusing Sensititre® plates, and the sequences of four ETH resistance-associated genes were analyzed based on genomic and PCR sequencing data.

RESULTS

Our results showed that 95.1% (39/41 isolates) of ETH-resistant isolates harbored at least one mutation in these four ETH resistance-associated genes. Most mutations were found in the inhA and ethA (including 5' untranslated region). Mutations in inhA region were mainly concentrated at the -777C>T site, whereas those in the ethA region were relatively scattered. Notably, multiple mutations were common in high-level ETH-resistant strains and were significantly associated with high-level resistance (P = 0.012). Furthermore, several novel single mutations in ETH-resistant strains, including inhA -100C>A, ethA -31G>A, and mshA Tyr155Ser, were detected.

CONCLUSION

Different individual mutations and multiple concurrent mutations in ETH resistance-associated genes are associated with varying levels of ETH resistance. These results broaden our understanding of the molecular characteristics of ETH resistance in China.