Abstract
Emergence of multidrug-resistant tuberculosis (MDR-TB) urgently demands for simple, rapid and inexpensive methods of its detection for the effective treatment of drug resistant tuberculosis, particularly in low-income countries. A total of 113 clinical isolates of M. tuberculosis were tested for four first line antitubercular drugs by nitrate reductase assay (NRA) and were compared with standard proportion method to evaluate NRA efficacy. Results were available in 7 - 14 days by NRA as compared to proportion method which generally takes 4 - 6 weeks. The sensitivity and specificity of NRA were 98.1% 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. Agreement between NRA and proportion method were 99.1%, 97.3%, 93.8%, 95.6% for isoniazid, rifampicin, streptomycin and ethambutol, respectively. NRA is easier, inexpensive and reliable method for susceptibility testing of Mycobacterum tuberculosis for isoniazid and rifampicin, the two most im- portant drugs for the treatment of tuberculosis. The reduction in susceptibility testing time, and higher sensitivity and specificity of NRA method is of fundamental importance in detecting MDR-TB.
Highlights
Emergence of multidrug resistant tuberculosis (MDR-TB) during the past ten years in higher rate represents a major public health problem, especially in low-resource countries where the burden of the disease is higher
A total of 113 clinical isolates of M. tuberculosis were tested for four first line antitubercular drugs by nitrate reductase assay (NRA) and were compared with standard proportion method to evaluate NRA efficacy
Eighty three isolates were from cases reported for pulmonary TB at National Tuberculosis Center (NTC), Thimi, Bhaktapur, Nepal, between November 2009 and May 2010; and thirty isolates were of proficiency testing strain from Supranational Reference Laboratory, Germany
Summary
Emergence of multidrug resistant tuberculosis (MDR-TB) during the past ten years in higher rate represents a major public health problem, especially in low-resource countries where the burden of the disease is higher. Conventional methods like proportion method (PM), the resistance ratio method and the absolute concentration method to detect drug resistance in Mycobacterium tuberculosis have traditionally relied on slow and cumbersome procedures requiring a minimum of 3 4 weeks to produce results [2] Other methods, such as the BACTEC 460 TB System [3], and oxidation-reduction dyes, e.g. tetrazolium [4], and Microplate Alamar Blue assay (MABA) [5], are faster but have the drawback of requiring either radioactive or expensive substrates, and are not feasible in most resource-poor settings. The use of specific reagents produces a change of color in the presence of nitrites indicating a positive result [6] Since it is described around the globe as simpler, cheaper and rapid, evaluation of NRA as an alternative method for determining M. tuberculosis susceptibility to rifampicin (RIF), isoniazid (INH), streptomycin (STR) and ethambutol (EMB) in our laboratory setting which is technically insufficient is necessary
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