[Comparative study and sensitivity tests of Mycobacterium tuberculosis strains using nitrate reductase and absolute concentrations methods]. / Studiu comparativ al testarii sensibilitatii tulpinilor de Mycobacterium tuberculosis prin metoda nitrat reductazei si metoda concentratiilor absolute.

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.

The concordance between phenotypic and genotypic M. tuberculosis drug susceptibility tests results: observational study.

UNLABELLED: Multi-drug resistant tuberculosis (MDR-TB) represents a major threat for TB control at the global level. Identification of mutations responsible for drug resistance by molecular methods can be used for rapid and specific detection of drug resistance. The aim of our study was to assess the concordance between phenotypic and genotypic tests results (GenoTypeMTBDRplus kit) for isoniazid and rifampicin resistance in M. tuberculosis isolated strains. MATERIAL AND METHODS: The specific zone mutations in rpoB, katG and inhA gene for rifampicin and isoniazid were investigated with molecular methods in 198 recently isolated unique strains from patients diagnosed with pulmonary tuberculosis. These results were compared with the absolute concentration drug susceptibility test results. RESULTS: Sensitivity, specificity, predictive positive value, predictive negative value, efficiency of genotypic method, calculated by comparing with conventional method for INH and RMP were 93.85%, 100.00%, 100.00%, 63.33%, 94.44%, and 99.26%, 82.25%, 92.46%, 98.07% and 93.93%, respectively). Cohen coefficient showed Kappa values = 0.746 (good strength of agreement) for INH, and Kappa value = 0.853 (very good strength of agreement) for RMP. CONCLUSION: The obtained results are consistent with those reported from other regions of the world. The use of rapid molecular assays reduces the time for drug resistance diagnostic to just a few days, and may help the control of the ongoing TB transmission.