Rapid Colorimetric Resazurin Microtiter Assay (REMA) and MTT Assay for Testing Susceptibility of Mycobacterium Tuberculosis to Isoniazid and Rifampici

Abstract

Background: According to World Health Statistics, an incidence rate of 15 per 100,000 population of tuberculosis in Egypt was reported. Percentage of Multidrug Resistance (MDR) among new TB cases was 3.4%, while among previously treated TB cases was 15%. Several methods have been developed for the rapid detection of drug resistance tuberculosis compared with conventional time consuming drug susceptibility testing (DST). These methods include phenotypic assays which are easier to perform and shorten the turnout time for the diagnosis of MDR-TB . Objective: The aim of this study was to evaluate performance of two phenotypic methods for testing Mycobacterium tuberculosis susceptibility to Isoniazid (INH) and Rifampicin (RMP), with reference to the conventional proportion method (PM). Methodology: 30 Mycobacterium tuberculosis isolates were tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (MTT) and resazurin microtiter assay (REMA), and compared with the results obtained with the gold standard methods: the proportion method on Lowenstein–Jensen medium. Results: Accuracy of 89.3% for INH and of 94.1% for RMP was observed using REMA assay, while accuracy of 96.9% for INH and of 93.2% for RMP was detected using MTT assay. Conclusion: MTT assay was noted to be more accurate than REMA assay. However, both assays are simple to perform for the rapid detection of Isoniazid and Rifampicin resistance and economically inexpensive. It is potentially useful for low-resource countries.