Non-commercial phenotypic assays for the detection of Mycobacterium tuberculosis drug resistance: a systematic review.

Several rapid non-commercial culture-based methods and assays for drug susceptibility testing (DST) of Mycobacterium tuberculosis have emerged over the last decades. The aim of the current review was to summarise evidence on the performance of microscopic observation of drug susceptibility (MODS), thin-layer agar (TLA) and colorimetric redox-indicator (CRI) assays for detection of resistance to first- and second-line anti-tuberculosis (TB) drugs. Forty-three publications satisfying selection criteria were selected for data extraction. MODS and CRI assays demonstrated pooled sensitivity and specificity of > 93% for the detection of resistance to rifampicin and isoniazid and confirmed their utility for an accurate detection of multidrug-resistant TB (MDR-TB) in various settings. Sensitivity and specificity values for indirect DST for ethambutol (EMB) using CRI assays were 94.0% and 82.0%, respectively, suggesting that CRIs could be used to rule out resistance to EMB. Performance for other drugs varied more substantially across the reports. There was no sufficient evidence on the performance of the TLA assay for making any conclusion on its utility for DST. Our data suggests that non-commercial assays could be used for a rapid and accurate DST in settings where the use of commercial World Health Organization-endorsed assays could be limited due to a variety of reasons including limited resources, laboratory facilities or trained personnel. While inexpensive and easy-to-perform MODS and TLA assays can be used in low-income settings, using CRI assays for determination of minimal inhibitory concentrations may be implemented in middle- and high-income countries with high MDR-TB burden to guide clinical management of TB patients.

Role of Alanine Racemase Mutations in Mycobacterium tuberculosis d-Cycloserine Resistance.

A screening of more than 1,500 drug-resistant strains of Mycobacterium tuberculosis revealed evolutionary patterns characteristic of positive selection for three alanine racemase (Alr) mutations. We investigated these mutations using molecular modeling, in vitro MIC testing, as well as direct measurements of enzymatic activity, which demonstrated that these mutations likely confer resistance to d-cycloserine.

Transcontinental spread and evolution of Mycobacterium tuberculosis W148 European/Russian clade toward extensively drug resistant tuberculosis.

Transmission-driven multi-/extensively drug resistant (M/XDR) tuberculosis (TB) is the largest single contributor to human mortality due to antimicrobial resistance. A few major clades of the Mycobacterium tuberculosis complex belonging to lineage 2, responsible for high prevalence of MDR-TB in Eurasia, show outstanding transnational distributions. Here, we determined factors underlying the emergence and epidemic spread of the W148 clade by genome sequencing and Bayesian demogenetic analyses of 720 isolates from 23 countries. We dated a common ancestor around 1963 and identified two successive epidemic expansions in the late 1980s and late 1990s, coinciding with major socio-economic changes in the post-Soviet Era. These population expansions favored accumulation of resistance mutations to up to 11 anti-TB drugs, with MDR evolving toward additional resistances to fluoroquinolones and second-line injectable drugs within 20 years on average. Timescaled haplotypic density analysis revealed that widespread acquisition of compensatory mutations was associated with transmission success of XDR strains. Virtually all W148 strains harbored a hypervirulence-associated ppe38 gene locus, and incipient recurrent emergence of prpR mutation-mediated drug tolerance was detected. The outstanding genetic arsenal of this geographically widespread M/XDR strain clade represents a "perfect storm" that jeopardizes the successful introduction of new anti-M/XDR-TB antibiotic regimens.

A successful introduction to a non-expert setting of the thin-layer agar Colour Test as an indirect phenotypic drug susceptibility test for Mycobacterium tuberculosis.

OBJECTIVES: We evaluated the performance of the MDR/XDR-TB Colour Test (CT) as an in-house thin-layer agar-based indirect drug susceptibility test (DST) for Mycobacterium tuberculosis (MTB) in a non-expert setting in Estonia. METHODS: After 2 days of hands-on training for laboratory technicians, 6 panels of 150 MTB isolates were cultured onto CT plates prepared in-house in 2 laboratories. Triplicate readings of 900 CT plates resulted in 18 DST patterns for each initial isolate. Time intervals to the results and for media preparation were estimated, and intra- and interobserver agreement, test sensitivities and specificities were calculated. BACTEC MGIT 960 DST was used as a reference. RESULTS: The median time to produce DST results for isoniazid, rifampicin and levofloxacin was 13 days. CT sensitivity was 94.7% for levofloxacin, 95.8% for isoniazid and 97.3% for rifampicin. Test specificities were >97% for all 3 drugs. Interobserver agreement was 100% in Lab A and in Lab B >97% for levofloxacin and 99% for isoniazid and rifampicin. CONCLUSIONS: The implementation of the CT into a new laboratory was straightforward with only minimal guidance required. This study proves that the CT is highly reproducible and easily interpreted by previously inexperienced personnel.