Characterization of rpoB Gene Mutations in Clinical Isolates of Mycobacterium TB

Abstract

SESSION TITLE: Tuberculosis SESSION TYPE: Original Investigation Poster PRESENTED ON: Wednesday, October 26, 2016 at 01:30 PM - 02:30 PM PURPOSE: 1) to evaluate the phenotypic characteristics of the specific mutation site, 2) to compare the performance of phenotypic and genotypic (molecular) susceptibility test for rifampin (RIF), 3) to define mutation sites which are correlated with RIF resistance levels and rifabutin (RBU) resistance. METHODS: Conventional phenotypic drug susceptibility testing (DST) in Middlebrook 7H10 medium, rpoB gene sequencing for 1kb around RIF resistance determining region (RRDR), and molecular DST (GenoType® MTBDRplus assay, MTBDRplus) were performed for 674 clinical isolates of M. tuberculosis which were obtained from the patients who had failed with first-line therapy. RESULTS: Based on conventional phenotypic DST 502 (74.5%) isolates were resistant to RIF. The rpoB gene sequencing showed 491 isolates possessed 517 mutation sites in the RRDR. The most frequent mutated site was codon 531 (185/517, 35.7%). Among the RIF-resistant isolates having the mutations at codon 533, most of the isolates (89%) showed minimal inhibitory concentration (MIC) lower than 16 ug/ml, suggesting that the mutation at codon 533 may not be associated with a high level of RIF resistance. Moreover, mutations at codon 533 (44/64, 68.8%) were frequently found in RIF-resistant and RBU-susceptible isolates. Sensitivity and specificity of the the rpoB gene sequencing and MTBDRplus were 93.4%, 91.4% and 91.4%, 95.1% respectively. CONCLUSIONS: Mutations at codon 533 were frequently found in clinical isolates of M. tuberculosis which were RIF-susceptible, low level resistant or RBU-susceptible. CLINICAL IMPLICATIONS: Physicians can expect phenotypic RIF- susceptible or RBU-susceptible despite of rpoB gene mutation if the mutation site is codon 533. DISCLOSURE: The following authors have nothing to disclose: Yangjin Jegal, Jihee Jung, Nackmoon Sung No Product/Research Disclosure Information