Determination of MIC Distribution and Epidemiological Cutoff Values for Bedaquiline and Delamanid in Mycobacterium tuberculosis Using the MGIT 960 System Equipped with TB eXiST

Abstract

Because of the new mechanism of action of bedaquiline-the compound acts via inhibition of mycobacterial ATP synthase (AtpE)-it has been postulated that antimicrobial susceptibility testing (AST) is not needed in patients who have never received bedaquiline (4). However, cross-resistance between bedaquiline and the antimycobacterial drug clofazimine through overproduction of the MmpL5 efflux pump has recently been described (5, 6). Thus, resistance may develop independently of treatment with bedaquiline (2, 7). Delamanid (Deltyba [previously known as OPC-67683]; marketed by Otsuka Novel Products GmbH, Munich, Germany) was approved by the European Medicines Agency (EMA) in April 2014. The mechanism of action of delamanid is incompletely understood; delamanid is suggested to inhibit production of methoxymycolic acid and ketomycolic acid (8). Similarly to the related drug PA-824, delamanid is a prodrug requiring activation by the mycobacterial F420 system, including the nitroreductase Ddn (Rv3547) (8-10). Delamanid resistance is thought to arise from mutations in the mycobacterial F420 genes (ddn, fgd1, fbiA, fbiB, and fbiC) associated with the prodrug's activation (8, 11). The spontaneous rate of delamanid resistance has been reported to be as high as 6.44 ϫ 10 Ϫ6 to 4.19 ϫ 10 Ϫ5 , emphasizing the need to protect delamanid with other active anti-TB drugs during therapy (9).Initially, AST of bedaquiline was reported using radiometric Bactec 460TB (BD, Franklin Lakes, NJ, USA), production of which has since been discontinued (2). Reported MIC 90 s for delamanid range from 0.006 mg/liter to 0.05 mg/liter (depending on the test system) across Mycobacterium tuberculosis isolates (8,9,12). Ten years after the drugs' discoveries, established protocols for automated in vitro AST of bedaquiline and delamanid are still not available. To establish procedures for bedaquiline and delamanid AST, we used well-characterized, fully drug-susceptible clinical M. tuberculosis strains of bedaquiline and delamanid treatment-naive patients, MDR-TB strains, and subsequent isolates of a well-characterized extensively drug-resistant (XDR) strain (6). It has been speculated that the phylogenetic lineage of the M. tuberculosis complex may affect innate drug susceptibility (13). To assess the phylogenetic diversity of the set of strains studied, all M. tuberculosis strains included underwent genotypic characterization by mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) analysis using a GenoScreen MIRU-VNTR typing kit (GenoScreen, Paris, France) according to the manufacturer's description. In order to determine the quality control (QC) MIC value, the pan-susceptible M. tuberculosis H37Rv reference strain was used. Details about the resistance patterns of the strains and genotypes are shown in Table S1 and S2 in the supplemental material. With the view to facilitating implementation in the routine laboratories, we used a semiautomated MGIT 960 system and EpiCenter software equipped with a TB eXiST module for q...

Bedaquiline susceptibility test for totally drug-resistant tuberculosis Mycobacterium tuberculosis

“…The reported MICs for bedaquiline-sensitive strains were 0.03-0.12 mg/L, considerably lower than those found in our study (Andries et al, 2005). However, Keller et al (2015) and Torrea et al (2015) reported that the MGIT 960 system equipped with EpiCenter/TB eXiST showed significantly higher MIC values than did the DAC system. The system reported bedaquiline MIC arithmetic means and medians of 0.54 mg/L and 0.4 mg/L, respectively, for the H37Rv strain.…”

A Multilaboratory, Multicountry Study To Determine Bedaquiline MIC Quality Control Ranges for Phenotypic Drug Susceptibility Testing

“…In addition, the bedaquiline MIC QC range using the broth microdilution method is not applicable to the widely used mycobacterial growth indicator tube (MGIT; Becton Dickinson) system (28), a commercial rapid liquid culture system for diagnosis and DST. Studies have been done to determine the mean bedaquiline MIC values (0.65 g/ml) (29) or ranges (Յ0.03 to 1.00 g/ml) (30) and epidemiological cutoffs (1.6 g/ml [29] and 1.0 g/ml [30]) for M. tuberculosis using the MGIT 960 system. However, these studies were not tier-2, multilaboratory, reproducibility studies, and in one of the studies (30), crushed tablets were used instead of pure powder.…”

Individualizing management of extensively drug-resistant tuberculosis: diagnostics, treatment, and biomarkers

“…Nowadays, the MGIT960 is the gold standard. However, treatment of MDR/XDR-TB should be individualized and based on a combination of true minimum inhibitory concentration (MIC) of drugs when testing the MTB isolate in vitro and the plasma levels that can be achieved in the respective patient [17,51,52]. This may become in reach of more laboratories when cheaper MIC methods will be standardized, like the 96-well Sensititre approach [53].…”

“…In high-burden settings, where resources are often limited, molecular resistance assays are used instead as they have a high throughput and superior performance characteristics to conventional culture and drug-susceptibility testing [108]. However, individualized treatment is based on true minimum inhibitory concentration (MIC) of drugs when testing the MTB isolate [17,51,52]. In addition to easy-to-implement MIC testing [109], a central reference laboratory is crucial for optimal treatment outcome in XDR-TB.…”