Bedaquiline- and clofazimine- selected Mycobacterium tuberculosis mutants: further insights on resistance driven largely by Rv0678.

Drug-resistant tuberculosis is a serious global health threat. Bedaquiline (BDQ) is a relatively new core drug, targeting the respiratory chain in Mycobacterium tuberculosis (Mtb). While mutations in the BDQ target gene, atpE, are rare in clinical isolates, mutations in the Rv0678 gene, a transcriptional repressor regulating the efflux pump MmpS5-MmpL5, are increasingly observed, and have been linked to worse treatment outcomes.

Unexpected high prevalence of resistance-associated Rv0678 variants in MDR-TB patients without documented prior use of clofazimine or bedaquiline.

Objectives: Resistance-associated variants (RAVs) in Rv0678 , a regulator of the MmpS5-MmpL5 efflux pump, have been shown to lead to increased MICs of bedaquiline (2- to 8- fold) and clofazimine (2- to 4-fold). The prevalence of these Rv0678 RAVs in clinical isolates and their impact on treatment outcomes are important factors to take into account in bedaquiline treatment guidelines.

Methods: Baseline isolates from two bedaquiline MDR-TB clinical trials were sequenced for Rv0678 RAVs and corresponding bedaquiline MICs were determined on 7H11 agar.

Mycobacterium tuberculosis whole genome sequencing and protein structure modelling provides insights into anti-tuberculosis drug resistance.

Background: Combating the spread of drug resistant tuberculosis is a global health priority. Whole genome association studies are being applied to identify genetic determinants of resistance to anti-tuberculosis drugs. Protein structure and interaction modelling are used to understand the functional effects of putative mutations and provide insight into the molecular mechanisms leading to resistance.

Correlation of different phenotypic drug susceptibility testing methods for four fluoroquinolones in Mycobacterium tuberculosis.

Background: Molecular resistance testing fails to explain all fluoroquinolone resistance, with a continued need for a suitable rapid phenotypic drug susceptibility testing method.

Objective: To evaluate the optimal method for phenotypic fluoroquinolone susceptibility testing.

Methods: Using Löwenstein-Jensen medium, Middlebrook 7H11 agar, BACTEC-MGIT 960 and the resazurin microtitre plate assay, we determined susceptibility to fluoroquinolones in Mycobacterium tuberculosis and investigated cross-resistance between ofloxacin, levofloxacin, moxifloxacin and gatifloxacin.

Specific gyrA gene mutations predict poor treatment outcome in MDR-TB.

Objectives: Mutations in the gyrase genes cause fluoroquinolone resistance in Mycobacterium tuberculosis. However, the predictive value of these markers for clinical outcomes in patients with MDR-TB is unknown to date. The objective of this study was to determine molecular markers and breakpoints predicting second-line treatment outcomes in M.

Bedaquiline susceptibility testing of Mycobacterium tuberculosis in an automated liquid culture system.

Objectives: The objective of this study was to evaluate the performance of the BACTEC MGIT960 system to test the susceptibility to bedaquiline for Mycobacterium tuberculosis complex.

Methods: We determined the quality control (QC) range of bedaquiline using the M. tuberculosis H37Rv reference strain and the epidemiological cut-off (ECOFF) in MGIT960 and on Middlebrook 7H11 agar (M7H11) using 47 strains from bedaquiline treatment-naive patients.

Acquired resistance of Mycobacterium tuberculosis to bedaquiline.

Bedaquiline (BDQ), an ATP synthase inhibitor, is the first drug to be approved for treatment of multi-drug resistant tuberculosis in decades. In vitro resistance to BDQ was previously shown to be due to target-based mutations. Here we report that non-target based resistance to BDQ, and cross-resistance to clofazimine (CFZ), is due to mutations in Rv0678, a transcriptional repressor of the genes encoding the MmpS5-MmpL5 efflux pump.