Primary Clofazimine and Bedaquiline Resistance among Isolates from Patients with Multidrug-Resistant Tuberculosis

Abstract

Clofazimine has been repurposed for the treatment of tuberculosis, especially for multidrug-resistant tuberculosis (MDR-TB). To test the susceptibility to clofazimine of Mycobacterium tuberculosis clinical isolates, MICs of clofazimine were determined using the microplate alamarBlue assay (MABA) method for 80 drugresistant isolates and 10 drug-susceptible isolates for comparison. For five clofazimineresistant strains isolated from previously treated pre-extensively drug-resistant TB (pre-XDR-TB) and XDR-TB patients without prior exposure to clofazimine or bedaquiline, clofazimine MICs were Ն1.2 g/ml. Four isolates with cross-resistance to bedaquiline had Rv0678 mutations. The other isolate with no resistance to bedaquiline had an Rv1979c mutation. This study adds to a recent study showing that 6.3% of MDR-TB patients without prior clofazimine or bedaquiline exposure harbored isolates with Rv0678 mutations, which raises concern that preexisting resistance to these drugs may be associated with prior TB treatment. Furthermore, we propose a tentative breakpoint of 1.2 g/ml for clofazimine resistance using the MABA method. Morewidespread surveillance and individualized testing for clofazimine and bedaquiline resistance, together with assessment of their clinical usage, especially among previously treated and MDR-TB patients, are warranted.

Drug resistance mechanisms and drug susceptibility testing for tuberculosis

“…However, it is hypothesized that the outer membrane could be a possible target and the mycobacterial integration host factor (mHIF) was recently proposed as a possible target of CFZ . Mutations in the transcriptional repressor Rv0678 ( mmpL5 ) cause upregulation of efflux protein Mmpl5, and are associated with CFZ resistance and cross‐resistance to BDQ . In addition, mutations in rv1979c encoding a putative permease and rv2535c encoding a peptidase PepQ are also associated with CFZ resistance in in vitro resistant mutants and also in MDR‐TB strains …”

“…For this reason, cross‐resistance of CFZ and BDQ might occur. Mutations such as V1A, S63R and nonsense mutation in codon 134 have been reported in BDQ resistance . In addition, mutation at the target gene, atpE (A63P and I66M), have been shown to confer resistance to BDQ …”

“…92 Mutations in the transcriptional repressor Rv0678 (mmpL5) cause upregulation of efflux protein Mmpl5, and are associated with CFZ resistance and cross-resistance to BDQ. 28,29,93 In addition, mutations in rv1979c encoding a putative permease and rv2535c encoding a peptidase PepQ are also associated with CFZ resistance in in vitro resistant mutants 29 and also in MDR-TB strains. 93 Add-on agents (groups D2 and D3) BDQ and DLM are among the group D2 of add-on agents.…”

“…28,29,93 In addition, mutations in rv1979c encoding a putative permease and rv2535c encoding a peptidase PepQ are also associated with CFZ resistance in in vitro resistant mutants 29 and also in MDR-TB strains. 93 Add-on agents (groups D2 and D3) BDQ and DLM are among the group D2 of add-on agents. BDQ (previously known as TMC-207) belongs to the class of diarylquinolines and shows activity towards both replicating and a population of nonreplicating tubercle bacilli.…”

“…Mutations such as V1A, S63R and nonsense mutation in codon 134 have been reported in BDQ resistance. 28,30,93 In addition, mutation at the target gene, atpE (A63P and I66M), have been shown to confer resistance to BDQ. 95 DLM (previously known as OPC-67683) is a derivative of nitroimidazole and inhibits mycolic acid synthesis.…”