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Comparative evaluation of Mycobacterium tuberculosis drug susceptibility testing between Direct Nitrate Reductase assay and Direct Proportion Method

Neelu Jain, Nitin Jain, Vaishali Jain.


Background: Drug resistance – multi-drug resistant (MDR) and extensive drug resistant (XDR) in tuberculosis (TB) is a matter of great concern for TB control programs. There is concern and need for early diagnosis of these multi-drug-resistant strains for better treatment.

Objective: To compare the usefulness of Nitrate Reductase Assay (NRA) and direct proportion as a tool for rapid and accurate detection of resistance to first line anti-tubercular drugs.

Material and Methods: A total of 120 sputum-positive AFB smears of pulmonary tuberculosis (PTB) patients were selected for the study. The samples were processed by NRA and direct proportion for assessment of drug susceptibility testing to first line anti-tubercular drugs.

Results: The sensitivity of NRA was 100%, 92.30%, 81.81%, and 72.72 % for RIF, INH, EMB, and STR, respectively. The specificity of NRA was 100%, 100%, 96.33%, and 89.79% for RIF, INH, EMB, and STR, respectively. The performance of NRA susceptibility testing was rapid and the median time of obtaining results was shorter using NRA (10 days) as compared to PM (28 days).

Conclusion: Direct NRA is simple, easy to perform, rapid, relatively less expensive, without requirement of expensive reagents and sophisticated equipments. It is useful tool suitable for early determination, first line anti-tubercular drugs namely rifampicin, isoniazid, ethambutol, and streptomycin with excellent concordance for INH and RIF resistance and relatively low accuracy for streptomycin, with good sensitivity and specificity.

Key words: Tuberculosis, multidrug resistant, Nitrate Reductase Assay

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