Objective To investigate the expression of sigma factor-sigG regulated genes of clpB, dnak, fadE5, lexA, and trxB in Mycobacterium tuberculosis with different drug resistance phenotypes, and evaluate their roles in the drug resistance mechanism and their relationship with drug resistance gene katG and rpoB.

Methods A retrospective analysis was conducted by using the rifampicin and isoniazid mono-resistant, multi-drug resistant, and fully sensitive M. tuberculosis strains collected from the outpatients in Tianjin Tuberculosis Control Center from 2018 to 2023. Melting curve drug resistance gene detection was performed for the collected strains. The strains with katG and rpoB mutations, combined mutations, and without mutations were included in the experimental study. RNA was extracted from the logarithmic phase of the included strains, and the expression levels of clpB, dnak, fadE5, lexA, and trxB genes were detected by quantitative real-time PCR (RT-PCR). The relative expression levels of the genes were detected by 2^−ΔΔCt analysis. Mann-Whitney U test was used to analyze the differences in gene expression between the drug-resistant group and the fully sensitive group, χ² test was used to analyze the differences in the high expression level of the genes between the drug-resistant groups and the fully sensitive group and two-way ANOVA was used to analyze the differences in expression levels between two groups.

Results Through melting curve drug resistance gene detection, 18 fully sensitive strains, 18 isoniazid mono-resistant strains, all with mutations in katG, 18 rifampicin mono-resistant strains, all with mutations in rpoB, and 18 multi-drug resistant strains, all with mutations in katG and rpoB were analyzed. In the isoniazid-resistant group, the relative expression level of the lexA gene was significantly higher than that in the sensitive group (P<0.05). In the rifampicin-resistant group, the expression level of the fadE5 gene was significantly higher than that in the sensitive group (P<0.05). In the multi-drug resistant group, the relative expression levels of the lexA and fadE5 genes were significantly higher than those in the sensitive group (all P<0.05). The expression rates of the fadE5 gene were all 100.00% in the four groups of included strains. The high expression rates of the clpB and lexA genes in the multi-drug resistant group were significantly higher than those in the sensitive group, the differences were significant (all P<0.05). Using sigA as the reference gene, the relative expression levels of lexA and fadE5 genes were significantly higher than those in the sensitive group indicated by two way ANOVO analysis (P<0.001).

Conclusion According to the three detection methods, lexA and fadE5 genes showed highly differential expressions in multidrug-resistant M. tuberculosis strains, which might play a role in the resistance mechanism of drug-resistant M. tuberculosis. Further studies are needed to investigate whether this specific mechanism is related to katG and rpoB mutations.