This study evaluated head-to-head rapid tests for drug susceptibility testing (DST) of Mycobacterium tuberculosis against rifampicin (RMP) and isoniazid (INH) in a resource-limited setting. Thirty-one well-characterized strains of M. tuberculosis were tested with the nitrate reductase assay (NRA), microscopic observation drug susceptibility (MODS), MGIT 960 (Mycobacterium Growth Indicator Tube 960), Genotype MTBDRplus, Alamar blue, MTT, and resazurin assays at the National TB Reference Laboratory and Department of Medical Microbiology, College of Health Sciences, Makerere University, Kampala, Uganda. The proportion method on Löwenstein-Jensen medium was used as the reference test. NRA correctly identified the resistant strains, with 100% sensitivity and specificity. MGIT 960 detected all multidrug-resistant strains but missed one RMP-monoresistant strain. Genotype MTBDRplus detected all RMP-resistant strains, but the sensitivity for detection of INH resistance was lower (88%). Sensitivity and specificity ranged from 86% to 100% for MODS and from 57% to 100% for the Alamar blue, MTT, and resazurin assays. Test results were obtained within 2-14 days. In the study setting, NRA, MGIT 960, and Genotype MTBDRplus gave excellent detection of multidrug-resistant TB, with significantly shorter time to results compared to conventional testing.
The International Journal of Tuberculosis and Lung Disease. 2010 Jul; Volume 14, Number 7: 890-5.
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