The objective of the study was to evaluate the performance of nitrate
reductase assay (NRA) as a rapid, reliable and inexpensive method for
drug-susceptibility testing (DST) of Mycobacterium tuberculosis against
firstline antitubercular drugs, such as rifampicin (RIF), isoniazid
(INH), streptomycin (STR), and ethambutol (EMB). In total, 286 isolates
were subjected to test by proportion method (PM) and NRA. By comparing
the results of NRA with those of the gold standard PM, sensitivities
and specificities were 98.4%, 97%, 88.5%, and 94.2% and 100%, 100%,
94%, and 99% for RIF, INH, STR, and EMB respectively. The positive
predictive values were 100%, 100%, 95%, and 98% for RIF, INH, STR, and
EMB respectively. The negative values were 99%, 98%, 87%, and 96% for
RIF, INH, STR, and EMB respectively. The median time of obtaining
results was shorter using NRA (10 days) compared to PM (28 days). An
excellent agreement was observed between the two phenotypic tests with
the \u3ba values of 0.98, 0.97, 0.81, and 0.93 for RIF, INH, STR, and
EMB respectively. The results demonstrated that NRA is suitable for the
early determination of INH and RIF resistance and has the potential to
be a useful tool for rapid drug-sensitivity test of M. tuberculosis in
resource-constrained settings