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Original papers

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

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.
Keywords: Multi-drug resistant tuberculosis (MDR TB), drug susceptibility tests, genetic testing, isoniazid, rifampicin