Characteristics of drug susceptibility testing for bedaquline and clofazimine of 178 drug-resistant Mycobacterium tuberculosis isolates in Japan

Background: Bedaquline (BDQ) plays a key role in the treatment for multidrug- and extensively drug-resistant tuberculosis (M/XDR-TB). The presence of drug resistance-associated variants (RAVs) as wild mutant strains are widely known. To obtain the resistant rate of BDQ for the patients without prior drug use in Japan, drug susceptibility testing using phenotypic and molecular methods (pDST/gDST) of clinical isolates were examined. Methods: A total of 178 M. tuberculosis isolates was collected from M/XDR-TB patients in Osaka Habikino Medical Center from 1998 to 2016. MGIT AST for BDQ and clofazimine (CFZ), the minimum inhibitory concentrations (MICs) for BDQ, and proportion method or MGIT AST for the diagnosis of M/XDR-TB were conducted from cloning strains. For the gDST, the whole genome sequencing was conducted using MiSeq (illumine), and RAVs in RV0678, atpE and pepQ were examined using TGS-TB (https://gph.niid.go.jp/tgs-tb/). As a control group, the RAVs of the drug susceptible isolates from TB survey of resistance in Japan, 2007 [RYOKEN. Int J Tuberc Lung Dis 2015:19(2):157-62] were determined. Results: 178 isolates included 135 M/XDR-TB. 16/178 (9.0%) RAVs in RV0678, atpE and pepQ were detected, and 7 of 10 mutated isolates in RV0678 showed high BDQ MIC (0.25-1.0 µg/ml) and BDQ resistance. 5 of 7 BDQ resistant isolates showed CFZ resistance. 1 of 106 nonmutated strains in RV0678 showed high BDQ MIC, but it was susceptible of MGIT AST. 106 control susceptible strains have only 1 (0.9%) RAVs in RV0678. Conclusion: Our data suggested that DST for BDQ and CFZ might be necessary for MDR/XDR-TB before the treatment.