Disk-based method for rapid determination of primary antituberculosis drug susceptibility in Mycobacterium tuberculosis.

Rapid and accurate determination of Mycobacterium tuberculosis susceptibility to primary drugs is critical for the timely initiation of effective therapy and the control of resistant tuberculosis (TB). This study aims to evaluate disk-based method for determining primary anti-TB drug susceptibility of M. tuberculosis isolates. A total of 67 M. tuberculosis isolates were used, of which 5 reference (M. tuberculosis H37Rv, ATCC-35822, ATCC-35838, ATCC-35820, ATCC-35837). Isolates were tested simultaneously with the nitrate reductase assay (NRA) and resazurin tube assay (RTA) versions in the newly developed disk-based method. Drug susceptibility test (DST) results were compared separately with the propotion method and BACTEC MGIT 960. When comparing DST results determined by disk-based NRA with MGIT 960, the agreement was 93.33 % for INH, 91.67 % for RIF, 78.33 % for STR, and 88.33 % for EMB; and when comparing with the proportion method, the agreement was 93.33 % for INH, 96.67 % for RIF, 91.67 % for STR, and 88.33 % for EMB. When comparing DST results determined by disk-based RTA with MGIT 960, the agreement was 95.16 % for INH, 91.94 % for RIF, 75.81 % for STR, and 91.94 % for EMB; and when comparing with the proportion method, the agreement was 95.16 % for INH, 96.77 % for RIF, 87.10 % for STR, and 88.71 % for EMB. The newly developed disk-based drug susceptibility method gives faster results than existing methods since it is applied together with colorimetric tests. It is more advantageous than other methods because it is disk-based in maintaining antibiotic stability. More studies are needed to evaluate its performance.