Evaluation of rapid low-cost colorimetric methods for diagnosis of multidrug-resistant tuberculosis in limited-resource settings

One third of the world\u27s population is currently infected with tuberculosis (TB), a consuming airborne disease whose main causative agent is Mycobacterium tuberculosis. The majority of these patients are found in the world\u27s poorest areas. Treatment of TB is a lengthy and demanding process utilizing a cocktail of powerful drugs; however, multidrug resistant TB (MDR-TB) strains, defined by resistance to both isoniazid (INH) and rifampicin (RIF), are now emerging worldwide and threatening disease control efforts. The major problem facing efforts to combat MDR-TB spread is its early detection. Conventional fairly affordable methods for drug resistance detection are based on solid culture and are highly time consuming (3-6 weeks in addition to initial pathogen culturing). On the other hand, the more rapid liquid culture-based automated systems are costly to set up and maintain while the very rapid molecular assays (hours to few days) are simply too complex and unaffordable and non-sustainable in limited resource settings. The objective of this work was to evaluate the performance of two liquid culture-based colorimetric assays for detection of drug resistance; nitrate reducate assay (NRA) and colorimetric redox indicator (CRI) methods for detection of MDR-TB. The assays were tested on mycobacterial isolates from Egyptian patients and their performance was compared with microscopic observation drug susceptibility assay (MODS) and the commercial automated culture system MGIT 960. Concordance was 96.7% for CRI and 93.3%, at almost one-tenth of the MGIT cost, and close to that of MODS without the need for an inverted microscope. The NRA format used in this study is more convenient and higher in throughput than the initially developed format. Additionally, DNA was extracted from the mycobacterial isolates and16S rDNA was amplified and sequenced to gain insight on the molecular diversity of Egyptian strains. Moreover, the molecular basis of strain resistance was investigated by DNA sequencing of the genes most commonly containing resistance conferring mutations. Analysis of the 16S rDNA sequencing results confirmed the identity of the samples as mycobacterium tuberculosis and suggested possible presence of two different strains. On the other hand, the analysis of the resistance related genes found common resistance conferring mutations in the MDR samples