Acquisition of Cross-Resistance to Bedaquiline and Clofazimine following Treatment for Tuberculosis in Pakistan

Aims and objectives: In the present study, we report on the first seven cases of acquired bedaquiline and clofazimine resistance identified in Pakistan. The study was conducted within the framework of a retrospective surveillance project to monitor the acquisition of resistance to bedaquiline implemented by the National TB Reference Laboratory in Pakistan and TB Supranational Reference Laboratory. Methods: Seventy three sequential isolates from 31 drug-resistant-tuberculosis patients on bedaquiline-containing regimens were retrospectively tested for bedaquiline resistance by MIC testing in 7H11 medium, and for all isolates showing an increased MIC compared to the baseline isolate, further MIC testing for bedaquiline and clofazimine was conducted using the Bactec MGIT960 (BD, Franklin Lakes, NJ, USA). The H37Rv (ATCC 27294) strain was used as a susceptible control in MIC testing. Bedaquiline dry powder was supplied by Janssen-Pharmaceutica (Beerse, Belgium). WGS was carried out with the Illumina Nextera-XT DNA sample preparation kit to prepare paired-end libraries of 150-bp read length to sequence on an Illumina NextSeq platform. Data analysis and single nucleotide polymorphism (SNP) calling were performed using the MTBseq-Pipeline on low-frequency detection mode. Genes associated with resistance to bedaquiline and/or clofazimine (atpE, Rv0678, pepQ, and Rv1979c) were screened for mutations. Results: We studied 73 isolates from patients (n=31; 8 MDR, 16 pre-XDR, and 7 XDR) enrolled in bedaquiline-containing regimens. The sequential isolates tested included two strains from 22 patients, three from 7 patients, and four from 2 patients. All baseline strains included in the study were sensitive to bedaquiline. Seven patients developed an increase in bedaquiline MICs in 7H11 medium (range, 0.125 to >0.5mg·liter−1) during therapy, and six of them became resistant to bedaquiline according to the current critical concentration proposed for the drug. In all seven patients we detected genetic variants in Rv0678 that were not present at baseline isolates. Moreover in five out of seven patients the treatment was ultimately failed. Conclusions: We documented cases failing therapy that developed specific mutations in Rv0678 and had increased MICs associated with cross-resistance to clofazimine during treatment. This study underlines the relevance of surveillance programs following the introduction of new drugs.