Evaluation of nitrate reductase assay for direct detection of drug resistance in Mycobacterium tuberculosis: rapid and inexpensive method for low-resource settings.

The aim of this study was to evaluate a nitrate reductase assay (NRA) for the direct detection of multidrug resistance (MDR) in Mycobacterium tuberculosis from 100 smear-positive sputum samples. The NRA results were compared with the reference proportion method for 100 sputum specimens for which comparable results were available. NRA results were obtained at day 7 for 61 specimens, results for 26 specimens were obtained at day 10, and the results for 13 specimens were obtained at day 14. Thus, 87% of NRA results were obtained in 10 days. NRA is a rapid, accurate, and cost-effective method for the detection of MDR in M. tuberculosis isolates as compared to the proportion method, which is time consuming. Therefore, NRA constitutes a useful tool for detection of tuberculosis drug resistance in low-resource countries with limited laboratory facilities due to its low-cost, ease of performance and lack of requirement of sophisticated equipment.