title: Evaluation of Direct Colorimetric MTT Assay for Rapid Detection of Rifampicin and Isoniazid Resistance in Mycobacterium tuberculosis.
abstract: With the spread of multidrug-resistant tuberculosis (MDR-TB) strains there is an increasing need for new accurate and cost-effective methods for a rapid diagnostic and drug susceptibility testing (DST), particularly in low-income countries where tuberculosis is hyperendemic. A colorimetric assay using 3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyltetrazolium bromide (MTT) has been suggested as a promising method for DST, especially to rifampicin. In this study, we standardized and evaluated the MTT assay for a rapid direct detection of rifampicin and isoniazid resistant Mycobacterium tuberculosis strains from sputum specimens using Lowenstein-Jensen (LJ) culture medium as a gold standard. The MTT assay sensitivity, specificity, positive and negative predictive values for rifampicin were 100%, 86%, 100%, 99%, respectively. For isoniazid, the MTT assay had a 100% sensitivity, specificity, positive and negative predictive values. Interestingly, the MTT assay gave interpretable results within two weeks for 94% of the samples compared to 7-14 weeks for LJ media. Overall, an excellent agreement was observed between MTT assay and LJ proportion method (Kappa, 0.91 for rifampicin and 1.00 for isoniazid). In conclusion, the direct colorimetric MTT assay simultaneously detects susceptible and resistant strains of M. tuberculosis within three weeks. It significantly shortens the time required to obtain a DST result and could be a reliable alternative method for rapid detection of drug-resistant TB strains in high-TB-burden resource-limited settings.
authors.affiliation: Department of Microbial, Cellular and Molecular Biology, College of Natural Sciences, Addis Ababa University, Addis Ababa, Ethiopia.
authors.forename: Gadissa Bedada
authors.identifier: http://orcid.org/0000-0002-5627-9675
authors.initials: GB
authors.lastname: Hundie
authors.affiliation: Biotechnology Institute, College of Natural Sciences, Addis Ababa University, Addis Ababa, Ethiopia.
authors.forename: Dawit
authors.initials: D
authors.lastname: Woldemeskel
authors.affiliation: Biotechnology Institute, College of Natural Sciences, Addis Ababa University, Addis Ababa, Ethiopia.
authors.forename: Amare
authors.initials: A
authors.lastname: Gessesse
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000995:Antitubercular Agents / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects*; D002648:Child; D003124:Colorimetry / Q000379:methods; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology*; D008297:Male; D008826:Microbial Sensitivity Tests / Q000379:methods*; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000302:isolation & purification*; D012293:Rifampin / Q000494:pharmacology*; D013183:Sputum / Q000382:microbiology; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D055815:Young Adult
chemical_list: D000995:Antitubercular Agents; D007538:Isoniazid; D012293:Rifampin