Evaluation of Direct Nitrate Reductase Assay for Drug Susceptibility Testing of Mycobacterium tuberculosis in Resource - Poor Settings

Direct Nitrate Reductase Assay (DNRA) was used for susceptibility testing of Mycobacterium tuberculosis to two front line anti-tuberculosis drugs (Rifampicin and Isoniacid) from 100 Acid fast bacilli smear-positive sputum samples. The DNRA results were compared with the gold standard conventional proportion method (PM). Ninety eight (98) sputum specimens result were comparable with the gold standard. DNRA results were obtained at day 10 for 72 specimens, results for 17 specimens were obtained at day 14, and the results for 9 specimens were obtained at day 18. Thus, 74 % of DNRA results were obtained in 10 days. The sensitivities and specificities of DNRA were 100 %, 97 % and 100 %, 99 % for Rifampicin and Isoniacid respectively. Positive predictive values were 100 % and 93 % for Rifampicin and INH respectively while negative predictive values were 97 % and 100 % for Rifampicin and Isoniacid respectively. NRA has been demonstrated as rapid, accurate, and cost-effective method for drug susceptibility testing of Mycobacterium tuberculosis. Therefore, NRA constitutes a useful tool for detection of tuberculosis drug resistance in low-resource countries.