Comparative study and sensitivity tests of Mycobacterium tuberculosis strains using nitrate reductase and absolute concentrations methods

INTRODUCTION: The alarming increase of cases of tuberculosis with resistant germs renders compulsory the orientation towards rapid and cheap methods that would allow large-scale testing of mycobacterial strains. AIM: Evaluation of the performances of two phenotypic methods for mycobacteria sensitivity testing. nitrate reductase and absolute concentrations. MATERIAL AND METHOD: In two different laboratories we tested the same set of 20 mycobacterial strains from the 2008/2009 international panel and an additional 10 strains isolated in the second laboratory, using the absolute concentration method as standard and the nitrate reductase method, both using Lowenstein Jensen medium with rifampicine and isoniaside incorporated The results obtained in both laboratories are concordant for both methods and show sensitivity and specificity of 100% for nitrate reductase method compared to absolute concentration method The results obtained using the two methods in the two laboratories also showed a 100% reproducibility. CONCLUSIONS: Nitrate reductase method is easy to perform and to acknowledge. It does not require special equipment, besides what is usually found in the laboratory. It showed a 100% sensitivity and specificity. The 100% reproducibility and repetability of results can represent arguments for a possible use of the methods in all the laboratories belonging to the national network of mycobacteriology laboratories, in order to screen for multiresistant strains.