Abstract：Objective To examine the association between the cross-resistance to ethionamide (Eto) and isoniazid (INH) and mutations of drug resistant genes in Mycobacterium tuberculosis (MTB), so as to provide the evidence for clinical diagnosis and treatment for multidrug-resistant (MDR) tuberculosis. Methods Totally 126 MTB clinical isolates were selected, including 88 MDR-MTB clinical isolates and 38 INH- and rifampicin (RFP)-sensitive isolates. The resistance to INH and Eto was tested in MTB clinical isolates using the drug susceptibility test, and the mutations in the spacer region of INH and Eto resistance-related katG, inhA, ethA, mshA, ndh, spacer region of oxyR-ahpC and inhA promoter were detected using PCR assay. The phenotypic resistance served as a gold standard, and the sensitivity, specificity and accuracy of gene mutation tests were calculated for detection of MTB clinical isolates cross-resistant to INH and Eto. Results Of the 126 MTB clinical isolates, there were 37 isolates cross-resistant to INH and Eto (29.37%), 51 isolates with resistance to INH and susceptibility to Eto (40.48%), 4 isolates with susceptibility to INH and resistance to Eto (3.17%) and 34 isolates with susceptibility to INH and Eto (26.98%). Among the 41 Eto-resistant MTB clinical isolates, there were 37 isolates with resistance to INH (90.24%). There were 64 MTB clinical isolates detected with katG mutations (50.79%), 4 isolates with mutation in the spacer region of oxyR-ahpC (3.17%), 2 isolates with inhA mutations (1.59%), and these isolates were all resistant to INH. There were 11 MTB clinical isolates detected with mutation in the inhA promoter (8.73%) and one isolate with ndh mutation, and all these isolates were cross-resistant to INH and Eto. There were 23 MTB clinical isolates detected with ethA mutations (18.25%) and 40 isolates with mshA mutations (31.75%), in which Eto-susceptible and -resistant isolates were detected. The diagnostic sensitivity, specificity and accuracy of inhA promoter tests for detection of cross-resistance to INH and Eto were 29.73% (95%CI: 16.44%-47.17%), 100.00% (95%CI: 87.36%-100.00%) and 63.38% (95%CI: 51.76%-73.63%) in MTB clinical isolates. Conclusions The prevalence of INH resistance is high in Eto-resistant MTB clinical isolates. Mutation in the inhA promoter region correlates with the cross-resistance to INH and Eto in MTB clinical isolates, and detection of mutation in the inhA promoter may be feasible to detect the cross-resistance to INH and Eto in MTB clinical isolates.
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