RESUMEN
Treatment of multidrug-resistance tuberculosis [MDR-TB] remains a challenge and its success depends on how quickly a case of TB is identified as drug resistant and whether an effective drug therapy is available. As a drug susceptibility test [DST], nitrate reductase assay [NRA] might help in management of MDR-TB patients. This study was conducted to evaluate NRA as a drug susceptibility test [DST] for the four primary anti-tuberculosis drugs [Isoniazide [INH], Rifampicin [RIF], Streptomycin [SM] and Ethambutol [EMB]]. A total of 30 isolates of M. tuberculosis were subcultured for 28 day to be fresh isolates and subjected to NRA. The results were recorded after 10 days of incubation and compared to that of the proportion method [PM] as a gold standard. Susceptibility testing for INH and RIF revealed relatively higher efficiencies when compared to that of the PM. For INH and RIF, the efficiencies were 93.3% and 90%, respectively. The sensitivity of the NRA as a DST for INH was 89.4%, while that for RIF was 93.3%. The specificities of NRA for INH and RIF were 100% and 86.6%, respectively. The predictive value of sensitivity for INH was 84.6% and that of RIF was 92.8%. The predictive value of resistance for INH was a high as 100%, while that of RIF was 87.5%. Susceptibility testing for SM and EMB showed relatively lower efficiency compared to PM. The efficiencies of NRA for SM and EMB were 86.6% and 76.6%, respectively. The sensitivity of the NRA as a DST for SM was 78.9%, while that for EMB was 40%. The specificity of the NRA for SM was 100% and that of EMB was 95%. The predictive values of sensitivity for SM and EMB were 73.3% and 76%, respectively. The predictive value of resistance for SM was 100% and that of EMB was 80%. NRA is a simple, rapid and inexpensive technique of high performance when used as susceptibility testing for both INH and RIF, but was not good for SM and EMB