Objective: This study aims to analyze the correlation between gene inhA  mutations by melting curve technology and phenotypic drug susceptibility (DST) results of ethionamide (ETH), and evaluate whether gene inhA  mutations detection can serve as a molecular marker in predicting ETH resistance.
Methods: A retrospective analysis was conducted on 382 strains of Mycobacterium tuberculosis  (MTB) with the anti-tuberculosis drugs isoniazid (INH), rifampicin (RIF), ETH, and others. Phenotypic drug susceptibility and the results of inhA  and katG genotypes (mutation and no mutation) were obtained using the melting curve technology MeltPro TB assay.
Results: Of the 382 clinical strains of MTB tested, 118 (30.9%) were resistant to INH, and 28 (7.3%) were resistant to ETH. Among the 28 phenotypically ETH-resistant strains, inhA  mutations accounted for 42.9% (12/28). These ETH-resistant strains comprise 35.3% (12/34) of the 34 inhA  mutant strains. Of 8 single inhA  mutation strains (without katG  or rpoB  mutation), 4(50%) were resistant to INH; however, all of these 8 strains were sensitive to ETH.
Conclusion: The inhA  mutation test may not be a reliable predictor of ETH resistance. Mutant inhA  strains are not necessarily resistant to ETH. The strains with single inhA mutation (without katG  or rpoB  mutation) may be effective for ETH treatment. The use of ETH in clinical medicine should be guided by gene (other than inhA  alone) detection and phenotypic drug susceptibility testing.
Keywords: melting curve technique, Mycobacterium tuberculosis , drug resistance, inhA , gene mutation, prothionamide, ethionamide