Abstract:
Criteria defining bedaquiline resistance for tuberculosis have been proposed addressing an emerging concern. We evaluated bedaquiline phenotypic drug susceptibility testing (pDST) criteria using drug-resistant tuberculosis clinical isolates tested at five reference laboratories. Isolates were tested at the proposed bedaquiline MGIT960 and 7H11 Agar Proportion (AP) critical concentrations, and dilutions higher. The epidemiological cut-off value for the broth microdilution (BMD) plates (frozen and dry) was investigated. Any isolate testing resistant had Sanger sequencing performed (atpE and Rv0678 genes). The composite reference standard (CRS) defined susceptibility or resistance as is, if all pDST methods agreed. If pDST was discordant sequencing results was used for final classification. Geographically-diverse and bedaquiline unexposed isolates were tested (N=495). The epidemiological cutoff value for BMD was confirmed to be 0.12 mug/mL. The majority of isolates were susceptible by all methods (467/495; 94.3%) and 28 were resistant by at least one method; of which 4 were resistant by all methods. 12/28 harboured Rv0678 mutations exclusively. Isolates with insertions/deletions were more likely to be resistant by more than one method (5/7) compared with isolates having a single nucleotide polymorphism (1/5). Applying the CRS to 24 discordant pDST, BMD dry correctly detected most (15/24; 63%), followed by MGIT960 and BMD frozen (13/24; 61%) and lastly AP (12/24; 50%). Applying the CRS, the prevalence of bedaquiline resistance was 2.2% and ranged from 1.4% to 3.4%, dependent on the method used. All methods performed well for bedaquiline susceptibility determination, however resistance detected should be investigated by a second alternative method.
