Discordant results for Mycobacterium tuberculosis isolates with disputed mutations between genotypic drug susceptibility testing (DST) (gDST) and phenotypic DST (pDST) impact RIF-resistant (RR) and multidrug-resistant (MDR) tuberculosis (TB) treatments due to a lack of practical clinical guidelines. To investigate the role of disputed rpoB mutations in M. tuberculosis and TB treatment outcomes, initial isolates of 837 clinical RR or MDR-TB cases confirmed during 2014-2018 were retested using agar-based RIF pDST and rpoB gene sequencing. Minimum inhibitory concentrations (MICs) were determined for isolates with disputed rpoB mutations. Disputed rpoB mutations were identified in 77 (9.2%) M. tuberculosis isolates, including 50 (64.9%) and 14 (18.2%) phenotypic RIF- and rifabutin (RFB)-resistant isolates, respectively. The predominant single mutations were L533P (44.2%) and L511P (20.8%). Most of the isolates harboring L511P (87.5%), H526N (100%), D516Y (70.0%) and L533P (63.6%) mutations had MICs ≤1 mg/L, whereas isolates harboring H526L (75%) had MICs > 1 mg/L. Of the 63 cases with treatment outcomes, 11 (17.5%) cases died, 1 (1.6%) case transferred out and 51 (81%) cases had favorable outcomes, including 8 and 20 cases treated with standard-dose RIF- and RFB-containing regimens, respectively. Excluding cases transferred out, received no or 1-day treatment, we observed statistically significant differences between active and inactive fluoroquinolones (FQs) [P =0.004, Odds ratio =0.05 (95% confidence intervals, 0.01-0.38)] in 57 cases. We concluded that disputed rpoB mutations are not rare. Depending on resources, sequencing and/or MIC testing is recommended for better management of RR and MDR-TB cases.

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis, is among the top 10 leading causes of death worldwide. The treatment course for TB is challenging; it requires antibiotic administration for at least 6 months, and bacterial drug resistance makes treatment even more difficult. Understanding the mechanisms of resistance is important for improving treatment. To investigate new mechanisms of isoniazid (INH) resistance, we obtained three INH-resistant (INH-R) M. tuberculosis clinical isolates collected by the Taiwan Centers for Disease Control (TCDC) and sequenced genes known to harbor INH resistance-conferring mutations. Then, the relationship between the mutations and INH resistance of these three INH-R isolates was investigated. Sequencing of the INH-R isolates identified three novel katG mutations resulting in R146P, W341R, and L398P KatG proteins, respectively. To investigate the correlation between the observed INH-R phenotypes of the clinical isolates and these katG mutations, wild-type katG from H37Rv was expressed on a plasmid (pMN437-katG) in the isolates, and their susceptibilities to INH were determined. The plasmid expressing H37Rv katG restored INH susceptibility in the two INH-R isolates encoding the W341R KatG and L398P KatG proteins. In contrast, no phenotypic change was observed in the KatG R146P isolate harboring pMN437-katG. H37Rv isogenic mutant with W341R KatG or L398P KatG was further generated. Both showed resistant to INH. In conclusion, W341R KatG and L398P KatG conferred resistance to INH in M. tuberculosis, whereas R146P KatG did not affect the INH susceptibility of M. tuberculosis.

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Tuberculosis (TB) is an infectious respiratory disease caused by Mycobacterium tuberculosis and one of the top 10 causes of death worldwide. Treating TB is challenging; successful treatment requires a long course of multiple antibiotics. Rifampicin (RIF) is a first-line drug for treating TB, and the development of RIF-resistant M. tuberculosis makes treatment even more difficult. To determine the mechanism of RIF resistance in these strains, we searched for novel mutations by sequencing. Four isolates, CDC-1, CDC-2, CDC-3, and CDC-4, had high-level RIF resistance and unique mutations encoding RpoB G 158 R, RpoB V 168 A, RpoB S 188 P, and RpoB Q 432 insQ, respectively. To evaluate their correlation with RIF resistance, plasmids carrying rpoB genes encoding these mutant proteins were transfected into the H 37 Rv reference strain. The plasmid complementation of RpoB indicated that G 158 R, V 168 A, and S 188 P did not affect the MIC of RIF. However, the MIC of RIF was increased in H 37 Rv carrying RpoB Q 432 insQ. To confirm the correlation between RIF resistance and Q 432 insQ, we cloned an rpoB fragment carrying the insertion (encoding RpoB Q 432 insQ) into H 37 Rv by homologous recombination using a suicide vector. All replacement mutants expressing RpoB Q 432 insQ were resistant to RIF (MIC > 1 mg/L). These results indicate that RpoB Q 432 insQ causes RIF resistance in M. tuberculosis.