Evaluation of Accuracy of Microplate Alamar Blue Assay and Proportion Method for Prompt Detection of Mycobacterium tuberculosis and Clinical Isolates of Multidrug-resistant M. tuberculosis

Abstract

Background: Tuberculosis is appraised to cause the deaths of more than a billion people in the last decades. Objectives: The current study compares the performance of microplate Alamar blue assay for clinical isolates of Mycobacterium tuberculosis and multidrug-resistant tuberculosis. Microplate Alamar blue assay was performed in a central tuberculosis laboratory at Golestan University of Medical Sciences in Gorgan, Iran. Methods: In the first step, the microplate Alamar blue assay was used for the detection of 78 clinical isolates in the Golestan regional tuberculosis reference laboratory, and the results were compared with those of the proportion assay. In the second step, the microplate Alamar blue assay and the proportion assay were used for the drug-susceptibility of 35 isolates. Results: In the microplate Alamar blue assay, the sensitivity was 100 (90.97 - 100), with a specificity of 74.36 (57.87 - 86.96), positive predictive value of 79.59 (65.66 - 89.76), and negative predictive value of 100 (88.06 - 100). For the microplate Alamar blue assay with rifampin, the sensitivity was 100 (89.11 - 100), specificity was 100 (29.24 - 100), positive predictive value was 100 (89.11 - 100), and negative predictive value was 100 (29.24 - 100). For the microplate Alamar blue assay with isoniazid, the sensitivity was 84.38 (67.21 - 94.72), specificity was 66.67 (9.43 - 99.16), positive predictive value was 96.43 (81.65 - 99.91), and negative predictive value was 28.57 (3.67 - 70.96). Conclusions: We found high accuracy between the microplate Alamar blue assay with rifampin and the proportion assay. The rapid and low-cost microplate Alamar blue assay is an inexpensive and appropriate assay for the detection of rifampin-resistant tuberculosis in low-income countries.