RAPID COLORIMETRIC MTT AND RESAZURIN ASSAYS FOR TESTING SUSCEPTIBILITY OF MYCOBACTERIUM TUBERCULOSIS TO CERTAIN FIRST-LINE ANTITUBERCULOSIS DRUGS

Abstract

SUMMARY T he emergence of drug-resistant M. tuberculosis is a global concern. Rapid, simple drug susceptibility tests that are applicable in developing countries would allow earlier treatment of patients with MDR infections. The aim of this study was to evaluate the Colorimetric MTT and REMA techniques, as phenotypic methods, for detecting drug resistance among M. tuberculosis strains. Thirty M. tuberculosis clinical strains were tested by colorimetric MTT and REMA methods. The results of both methods were compared to the gold standard proportional method. REMA assay results of drug susceptibility testing to INH showed that 19 isolates were resistant (MIC> 0.25μg/ml) and 11 isolates were sensitive (MIC ≤ 0.03μg/ml), and as for RMP 15 isolates were resistant (MIC> 0. 5μg/ml) and 15 were sensitive (MIC ≤ 0.25μg/ml). By comparing REMA assay results with those obtained by the PM, we found that when testing INH using REMA assay the sensitivity was 100.0%, and specificity was 78.6%, with 84.2% positive predictive value, 100% negative predictive value and 90% accuracy, and we found that when testing RMP using REMA assay the sensitivity was 88.2%, the specificity was 100%, with 100% positive predictive value, 86.7% negative predictive value and 93% accuracy. For MTT assay, results of drug susceptibility testing to INH showed that 15 isolates were resistant (MIC> 0.25μg/ml) and 15 isolates were sensitive (MIC ≤ 0.03μg/ml), while 17 isolates were resistant (MIC> 0. 5μg/ml) and 13 were sensitive (MIC ≤ 0.25μg/ml) to RMP. By comparing the results of the present study with those obtained by the PM, we found that when testing INH using MTT assay the sensitivity was 93.8%, the specificity was 100%, with 100.0% (PPV), 93.3% (NPV) and 96.6% accuracy, and we found that when testing RMP using MTT the sensitivity was 94.1%, the specificity was 92.3%, with 94.1% (PPV), 92.3% (NPV) and 93.3% accuracy.