Evaluation of the accuracy of the microplate alamar blue assay and the proportion method for the prompt detection of Mycobacterium tuberculosis and susceptibility of multidrug-resistant Mycobacterium tuberculosis clinical isolates

Aims and objectives: Tuberculosis (TB) is estimated to have caused the deaths of 1 billion people in the last 200 years. Methods: In the first step, the microplate alamar blue assay (MABA) was used for the detection of seventy-eight clinical isolates from Golestan Regional Tuberculosis Reference Laboratory (GRTRL) and the results were compared with the proportion method. In second step, the MABA was used for the susceptibility testing of 35 clinical isolates and the results were compared with the proportion method. Results: For the MABA, the sensitivity was 100 (90.97-100), specificity was 74.36 (57.87-86.96), positive predictive value (PPV) was 79.59 (65.66-89.76), negative predictive value (NPV) was 100 (88.06-100). The concentrations of isoniazid (INH) and rifampicin (RMP) ranged from 1.0-0.01 μg.mL and 2.0-0.03 μg.mL, respectively. For the proportion method, the INH concentration was between 1.0-0.03 μg.mL and the RMP concentration was between 2.0-0.06 μg.mL. For the MABA to RMP, the sensitivity was 100 (89.11-100), specificity was 100 (29.24-100), PPV was 100 (89.11-100), NPV was 100 (29.24-100), and for the MABA to INH, the sensitivity was 84.38 (67.21-94.72), specificity was 66.67 (9.43-99.16), PPV was 96.43 (81.65-99.91), NPV was 28.57 (3.67-70.96). Conclusion: We found the high accuracy between the MABA-RMP and the proportion method. In fact, the rapid and low-cost MABA assay is inexpensive and alternative assays for the detection of RMP resistant tuberculosis in low-income countries.