bedaquiline and resazurin

To describe the distributions of bedaquiline and linezolid MIC values for the Mycobacterium tuberculosis WT population and to define the corresponding epidemiological cut-offs (ECOFFs) in three Latin American countries.. MICs of bedaquiline and linezolid were determined by the resazurin microtitre assay (REMA). In phase 1, interlaboratory reproducibility was assessed using a panel of 10 fully susceptible M. tuberculosis strains. Phase 2 involved MIC determination for 248 clinical isolates from Argentina (n = 58), Brazil (n = 100) and Peru (n = 90) from patients who were treatment-naive for bedaquiline and linezolid. We then determined the ECOFFs for bedaquiline and linezolid by the eyeball method and the ECOFFinder statistical calculator.. Phase 1: REMA MIC values in the three sites were either identical to each other or differed by one 2-fold dilution from the consensus value with the exception of a single value. Phase 2: the bedaquiline MIC range was 0.0039-0.25 mg/L for pan-susceptible and drug-resistant isolates combined. The linezolid MIC range was 0.062-0.5 mg/L for pan-susceptible isolates and 0.031-4 mg/L for drug-resistant isolates. ECOFFs were 0.125 mg/L for bedaquiline and 0.50 mg/L for linezolid.. REMA is reproducible and robust for the determination of bedaquiline and linezolid MIC distributions and ECOFF values when applied in laboratories of medium/low-resource countries. We suggest that WT MIC distributions for both drugs should be used as a monitoring tool to control the possible rapid emergence of resistance.

Topics: Antitubercular Agents; Argentina; Brazil; Diarylquinolines; Drug Resistance, Multiple, Bacterial; Humans; Linezolid; Microbial Sensitivity Tests; Mycobacterium tuberculosis; Oxazines; Peru; Reference Values; Reproducibility of Results; Tuberculosis, Multidrug-Resistant; Xanthenes

The emergence of drug-resistant tuberculosis (TB) poses a serious challenge to existing anti-TB therapies. Hence, there is a direct need for identification of new drugs and effective combination regimens.. In this study, minimum inhibitory concentrations (MICs) of the anti-TB drugs bedaquiline (BDQ), delamanid (DEL) and moxifloxacin (MFX) were evaluated using a resazurin microtiter assay (REMA) against five drug-resistant clinicalMycobacterium tuberculosis (MTB) isolates as well as the drug-susceptible reference strain H37Rv. In addition, their fractional inhibitory concentration indices (FICIs) were evaluated using a REMA-based calorimetric chequerboard assay to assess their interaction profiles against the MTB isolates.. The FICI indicated that BDQ acted synergistically with DEL against isoniazid (INH)-monoresistant, rifampicin (RIF)-monoresistant and extensively drug-resistant (XDR) clinical MTB isolates. In addition, the combination of DEL acted synergistically with MFX against INH-monoresistant, RIF-monoresistant and XDR clinical MTB isolates. Moreover, the combination of BDQ and MFX showed a synergistic effect against RIF-monoresistant and pre-XDR clinical MTB isolates. DEL at 0.125×MIC (i.e. 0.015μg/mL) used in combination with BDQ at 0.25×MIC (i.e. 0.015μg/mL) had a stronger bactericidal effect against the XDR-TB clinical isolate than DEL alone at 1×MIC (i.e. 0.125μg/mL).. Synergistic and additive effects between these two-drug combinations offer an attractive chemotherapeutic regimen against drug-resistant clinical MTB isolates.

Topics: Antitubercular Agents; Diarylquinolines; Drug Resistance, Multiple, Bacterial; Drug Synergism; Extensively Drug-Resistant Tuberculosis; Humans; Microbial Sensitivity Tests; Moxifloxacin; Mycobacterium tuberculosis; Nitroimidazoles; Oxazines; Oxazoles; Tuberculosis, Multidrug-Resistant; Xanthenes

Targeting dormant Mycobacterium tuberculosis represents a challenge to antituberculosis drug discovery programs. We previously reported and validated the use of the streptomycin (STR)-dependent M. tuberculosis 18b strain as a tool for assessing drug potency against nonreplicating bacteria both in vitro and in vivo. In this study, we generated a luminescent 18b strain, named 18b-Lux, by transforming the bacteria with a vector expressing the luxCDABE operon from Photorhabdus luminescens. Luciferase expression was demonstrated under replicating conditions, and, more importantly, luminescence levels significantly above background were detected following STR removal. The sensitivity of STR-starved 18b-Lux to approved and candidate antituberculosis therapeutic agents was evaluated by means of a luciferase assay in a 96-well format. Results mirrored the data obtained with the standard resazurin reduction microplate assay, and the luminescence readout allowed time course assessments of drug efficacy in vitro. Specifically, we proved that bedaquiline, the rifamycins, and sutezolid displayed time-dependent activity against dormant bacteria, while pyrazinamide and SQ109 showed bactericidal effects at the highest concentrations tested. Overall, we established the optimal conditions for an inexpensive, simple, and very sensitive assay with great potential for future applications.

Topics: Adamantane; Antitubercular Agents; Colony Count, Microbial; Diarylquinolines; Drug Discovery; Ethylenediamines; Genes, Bacterial; Luminescence; Microbial Sensitivity Tests; Mycobacterium tuberculosis; Oxazines; Oxazolidinones; Photorhabdus; Pyrazinamide; Rifamycins; Xanthenes

The search for drugs that can kill replicating and nonreplicating Mycobacterium tuberculosis faces practical bottlenecks. Measurement of CFU and discrimination of bacteriostatic from bactericidal activity are costly in compounds, supplies, labor, and time. Testing compounds against M. tuberculosis under conditions that prevent the replication of M. tuberculosis often involves a second phase of the test in which conditions are altered to permit the replication of bacteria that survived the first phase. False-positive determinations of activity against nonreplicating M. tuberculosis may arise from carryover of compounds from the nonreplicating stage of the assay that act in the replicating stage. We mitigate these problems by carrying out a 96-well microplate liquid MIC assay and then transferring an aliquot of each well to a second set of plates in which each well contains agar supplemented with activated charcoal. After 7 to 10 days-about 2 weeks sooner than required to count CFU-fluorometry reveals whether M. tuberculosis bacilli in each well have replicated extensively enough to reduce a resazurin dye added for the final hour. This charcoal agar resazurin assay (CARA) distinguishes between bacterial biomasses in any two wells that differ by 2 to 3 log10 CFU. The CARA thus serves as a pretest and semiquantitative surrogate for longer, more laborious, and expensive CFU-based assays, helps distinguish bactericidal from bacteriostatic activity, and identifies compounds that are active under replicating conditions, nonreplicating conditions, or both. Results for 14 antimycobacterial compounds, including tuberculosis (TB) drugs, revealed that PA-824 (pretomanid) and TMC207 (bedaquiline) are largely bacteriostatic.

Topics: Agar; Antitubercular Agents; Biological Assay; Charcoal; Colony Count, Microbial; Coloring Agents; Diarylquinolines; Fluorometry; Microbial Sensitivity Tests; Mycobacterium tuberculosis; Nitroimidazoles; Oxazines; Xanthenes

Mycobacterium tuberculosis 18b, a streptomycin (STR)-dependent mutant that enters a viable but nonreplicating state in the absence of STR, has been developed as a simple model for drug testing against dormant bacilli. Here, we further evaluated the STR-starved 18b (SS18b) model both in vitro and in vivo by comparing the behavior of 22 approved and experimental tuberculosis drugs. Using the resazurin reduction microplate assay (REMA), rifampin (RIF), rifapentine (RPT), TMC207, clofazimine (CFM), and linezolid (LIN) were found to be active against SS18b in vitro, and their bactericidal activity was confirmed by determining the number of CFU. A latent 18b infection was established in mice, and some of the above-mentioned drugs were used for treatment, either alone or in combination with RIF. RIF, RPT, TMC207, CFM, and pyrazinamide (PZA) were all active in vivo, while cell wall inhibitors were not. A comparative kinetic study of rifamycin efficacy was then undertaken, and the results indicated that RPT clears latent 18b infection in mice faster than RIF. Intrigued by the opposing responses of live and dormant 18b cells to cell wall inhibitors, we conducted a systematic analysis of 14 such inhibitors using REMA. This uncovered an SS18b signature (CWPRED) that accurately predicted the activities of cell wall inhibitors and performed well in a blind study. CWPRED will be useful for establishing the mode of action of compounds with unknown targets, while the SS18b system should facilitate the discovery of drugs for treating latent tuberculosis.

Topics: Acetamides; Amino Acid Sequence; Animals; Antitubercular Agents; Clofazimine; Diarylquinolines; Disease Models, Animal; Drug Discovery; Drugs, Investigational; Female; Genetic Engineering; Latent Tuberculosis; Linezolid; Mice; Mice, Inbred BALB C; Microbial Sensitivity Tests; Molecular Sequence Data; Mycobacterium tuberculosis; Oxazines; Oxazolidinones; Quinolines; Rifampin; Streptomycin; Structure-Activity Relationship; Xanthenes