Rapid Molecular Assays for the Diagnosis of Drug-Resistant Tuberculosis

Abstract

The recognition that drug-resistant tuberculosis (DR-TB) poses a major threat to global tuberculosis (TB) control efforts has catalysed the development of new and urgently needed TB diagnostics. The full beneficial impact of the subsequent flood of new TB diagnostic tests into the market can only be realised if these diagnostic tests are readily accessible to TB programs and contribute to improved patient outcomes. Although phenotypic drug-susceptibility testing remains the gold standard, an improved understanding of the relationship between mutations and different levels of drug resistance coupled with the advantages of molecular diagnostics could result in rapid molecular diagnostic tests replacing phenotypic drug-susceptibility testing. Successful diagnostics need to diagnose all forms of drugresistant TB prevalent in each geographic region. Given the finite number and often limited availability of effective drugs for DR-TB, the diagnostic test must be able to detect all clinically important types of resistance to available anti-TB drugs. However, less comprehensive resistance profiling may be sufficient in settings where extensively drug-resistant TB (XDR-TB) and pre-XDR are absent. Rapid molecular diagnostic tests for DR-TB detection suitable for DR-TB endemic settings should be accurate, inexpensive, suitable to be performed on an easily accessible sample, detect prevalent circulating drug-resistant strains, and provide results within a short turnaround time to enable timely treatment initiation. In this review, we appraise the wide range of molecular diagnostics for DR-TB endorsed by the World Health Organisation, discuss the challenges in the development and rollout of rapid molecular DR-TB tests in low-and middle-income countries, and highlight user perspectives and cost-effectiveness factors that influence their utility.

Microfluidic systems for infectious disease diagnostics

“…194,195 Commercial microfluidic PCR assays include Xpert® MTB/ RIF (GeneXpert®, Cepheid, USA), a landmark development in TB diagnostics that detects MTBC bacteria and rifampicin (RIF) resistance within 2 h. 196 Xpert® MTB/RIF Ultra has improved sensitivity (LOD 15.6 CFU mL −1 for MTBC) and Xpert® MTB/XDR was designed for detection of mutations resistant to 6 anti-TB drugs within 90 min. 195 The VereMTB™ assay (VerePLEX™ Biosystem, Veredus Laboratories, Singapore) detects MTBC, several nontuberculous mycobacteria, as well as RIF and isoniazid (INH) resistance. Other WHO-endorsed on-chip RT-PCR assays are the Truenat® MTB, MTB Plus and MTB-RIF Dx assays (Molbio Diagnostics, India).…”

“…193 WHO-endorsed TB diagnostics has been reviewed recently by Nandlal et al and Hong et al , respectively. 194,195…”

Line Probe Assay for Rapid Diagnosis of Multidrug Resistant Pulmonary Tuberculosis

“…Also, isoniazid resistance is caused by mutations in the inhA promoter region, katG, ahpC, ndh, and furA genes. The majority of katG mutations are found at codon 315, which is responsible for increasing isoniazid resistance by 50% up to 90% 16 .…”

Whole blood vs serum-derived exosomes for host and pathogen-specific tuberculosis biomarker identification: RNA-seq based machine learning approach

“…The existing TB diagnostic tests are focused on detecting Mtb or speci c host immune responses using relatively faster, simpler and cost-effective methods, such as tuberculin skin test (TST), interferon-gamma release assays (IGRAs) (Loureiro et al 2019; Barker et al 2023) or nucleic acid ampli cation tests (NAATs), most commonly the polymerase chain reaction (PCR)-based tests (Chin et al 2018;Nandlal et al 2022). However, these routine diagnostic tests are not speci c for predicting disease progression (Pai and Sotgiu 2016) or distinguishing active disease from the latent infection (Carranza et al 2020).…”