title: Evaluation of direct method of drug susceptibility testing of Mycobacterium tuberculosis to rifampicin and isoniazid by nitrate reductase assay in a national reference laboratory.
abstract: The aim of this study was to evaluate a simple, rapid, and inexpensive colorimetric nitrate reductase assay (NRA) for direct drug susceptibility testing (DST) of Mycobacterium tuberculosis against rifampicin (RIF) and isoniazid (INH). A total of 118 smear-positive specimens were processed from patients on antituberculosis treatment. A comparison was made between the direct NRA of DST with the direct proportion method and with the internationally accepted indirect 1% proportion method as the "gold standard". The sensitivity and specificity of the direct NRA and indirect proportion method were 94% and 98%, and 100% and 98% for RIF and INH, respectively. Excellent agreement was found between the 2 tests with kappa values of 0.92 and 0.98, and P value was less than 0.001 for RIF and INH. The results in most cases were available in 14 days (turnaround time). The direct NRA is a rapid, accurate, simple, and inexpensive method to determine multidrug resistance from sputum. Direct NRA may become an appropriate alternative method, especially for the resource poor settings.
authors.affiliation: Department of Microbiology, LRS Institute of TB and Respiratory Diseases, New Delhi, India. pvishala@yahoo.com
authors.forename: Potharaju
authors.initials: P
authors.lastname: Visalakshi
authors.forename: Sandeep Kumar
authors.initials: SK
authors.lastname: Meharwal
authors.forename: Vittal Prasad
authors.initials: VP
authors.lastname: Myneedu
authors.forename: Degember
authors.initials: D
authors.lastname: Behera
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D003124:Colorimetry / Q000379:methods; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology*; D050901:Nitrate Reductase / Q000378:metabolism*; D012293:Rifampin / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D013997:Time Factors; D014376:Tuberculosis / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D050901:Nitrate Reductase; D007538:Isoniazid; D012293:Rifampin