DISCREPANCY ACROSS PHENOTYPIC AND GENOTYPIC RESULTS OF DRUG SUSCEPTIBILITY TESTING OF MYCOBACTERIUM TUBERCULOSIS

Abstract

Introduction: With increasing incidence of MDRTB accurate drug susceptibility testing (DST) of M.tuberculosis has become crucial for proper patient management. Aim: to evaluate the concordance across phenotypic and genotypic results of DST of M.tuberculosis for rapid diagnostic of MDRTB. Methods: Results across phenotypic (MGIT 960 system) and molecular methods (GenoType MTBDRplus&GeneXpert MTB/RIF) were evaluated to find the discrepancies in the DST results. Results: Among 1119 TB patients investigated by Xpert, 414 were susceptible and 630 were resistant to Rifampicin (R). Discordance across susceptible phenotypic and genotypic results was found in the 8.0% (n=36) of cases, discordance across resistant phenotypic and genotypic results was find in the 5.8% (n=39) of cases. Among 1259 patients investigated by MTBDRplus, 695 were susceptible and 509 were resistant to R. Discordance across susceptible phenotypic results and genotypic was find in the 4.1% (n=30) of cases, and in the 4.7% (n=25) of cases across resistant results. Discrepancies of results for Isoniazid was found in 2.6% (n=18) in susceptible cases and in 5.4% (n=31) among resistant cases. Conclusions: New diagnostic methods provide a promising solution for rapid detection of drug resistant TB. For reliable DST results, phenotypic and genotypic methods should be used in parallel, to be phased in without loss of existing culture and DST capacity. Our results have implications for the clinical interpretation of molecular diagnostics as efficient individualised therapy for patients with TB. Correlation of genotypic and phenotypic DST results can be crucial forward a personalized approach in MDRTB patient treatment.