The purpose of this study is to evaluate four rapid colourimetric methods, including
the resazurin microtitre assay (REMA), malachite green decolourisation assay (MGDA),
microplate nitrate reductase assay (MNRA) and crystal violet decolourisation assay
(CVDA), for the rapid detection of multidrug-resistant (MDR) tuberculosis.
Fifty Mycobacterium tuberculosis isolates were used in this
study. Eighteen isolates were MDR, two isolates were only resistant to isoniazid
(INH) and the remaining isolates were susceptible to both INH and rifampicin (RIF).
INH and RIF were tested in 0.25 µg/mL and 0.5 µg/mL, respectively. The agar
proportion method was used as a reference method. MNRA and REMA were performed with
some modifications. MGDA and CVDA were performed as defined in the literature. The
agreements of the MNRA for INH and RIF were 96% and 94%, respectively, while the
agreement of the other assays for INH and RIF were 98%. In this study, while the
specificities of the REMA, MGDA and CVDA were 100%, the specificity of the MNRA was
lower than the others (93.3% for INH and 90.9% for RIF). In addition, while the
sensitivity of the MNRA was 100%, the sensitivities of the others were lower than
that of the MNRA (from 94.1-95%). The results were reported on the seventh-10th day
of the incubation. All methods are reliable, easy to perform, inexpensive and easy to
evaluate and do not require special equipment.