Evaluation of Nitrate Reductase Assay For Rapiddetection of drugresistanttuberculosis

Abstract

Due to the emergence of multidrug-resistant tuberculosis (MDR-TB), there is an urgentdemand for simple, rapid and inexpensive methods of detecting drug resistanttuberculosisfor effectivetreatment, particularly in low-income countries.This study hasthe objective to evaluate nitrate reductase assay (NRA) efficacy for streptomycin,isoniazid, rifampicin and ethambutol susceptibility testing of Mycobacteriumtuberculosis strains.This prospective study was carried out at National TBReferenceLaboratory and SAARC TB and HIV/AIDS Centre, Thimi, Bhaktapur, Nepal fromNovember 2009 to May 2010.A total of113 clinical isolates ofM. tuberculosisweretested for four first line antitubercular drugs by nitrate reductase assay and werecompared with standard proportion method. The sensitivity and specificity of NRAwere98.1% and 100% for isoniazid, 95.1% and 98.6% for rifampicin,91.4% and 94.9%for streptomycin, and 78.6% and 97.9% for ethambutol respectively. AgreementbetweenNRA and proportion method were99.1%, 97.3%, 93.8%, 95.6%for isoniazid,rifampicin, streptomycin and ethambutol respectively.Results were available in 7-14days by NRAas compared to proportion method which takes 4-6 wk.NRA is reliablefor susceptibility testing of isoniazid and rifampicin, the two most important drugs forthe treatment of tuberculosis and is also easy to perform and inexpensive. In addition,the reduction in the timenecessary to obtain susceptibility results is of fundamentalimportance. Key words:Drug susceptibility,Mycobacterium tuberculosis,nitrate reductase assay,Proportion method