Molecular characteristics and in vitro susceptibility to bedaquiline of Mycobacterium tuberculosis isolates circulating in Shaanxi, China.

Objective: The aim of this study was to investigate the molecular characteristics and in vitro susceptibility to bedaquiline of Mycobacterium tuberculosis (MTB) isolates from Shaanxi, China.

Methods: The minimum inhibitory concentration (MIC) of bedaquiline was determined using the microplate alamarBlue assay for 518 MTB isolates from Shaanxi. Isolates with MIC values of bedaquiline ≥0.12 μg/mL were sequenced for the atpE, Rv0678, and pepQ genes. Drug susceptibility testing and spoligotyping were also conducted for all strains.

Results: Ten (1.93%) bedaquiline-resistant strains were isolated from 518 tuberculosis patients. The resistance rate of bedaquiline was not correlated to sex, age, treatment history, region, or genotype. Five bedaquiline-resistant isolates and one bedaquiline-susceptible isolate were found to carry Rv0678 mutations; six mutation types were identified, including G5T, A263G, C185T, G19deletion, C265T, and T323C. No mutations within the atpE and pepQ genes were observed.

Conclusions: Bedaquiline showed strong in vitro antibacterial activity against MTB isolates, and the Rv0678 gene serves as the major mechanism contributing to bedaquiline resistance among MTB isolates from Shaanxi, China. Three novel mutation types (G19deletion, C265T, and T323C) of the Rv0678 gene were associated with resistance to bedaquiline. Furthermore, in addition to the current three resistance-associated genes (atpE, Rv0678, and pepQ), other mechanisms of resistance to bedaquiline may exist that need further study.