Molecular detection of isoniazid and rifampin-resistant Mycobacterium tuberculosis strains from southwest of Iran

Abstract

Introduction and aim. The study of molecular mechanisms of resistance to first-line antibiotics for the treatment of tuberculosis is of great importance. Investigating these mechanisms provides valuable information to treatment policy makers. Therefore, this study aimed to identify mutations associated with resistance to rifampin (RIF) and isoniazid (INH) among drug-resistant Mycobacterium tuberculosis (MTB) isolates from a TB reference center in southwest Iran. Material and methods. In this cross-sectional study (September 2014-February 2018), a total of 772 MTB isolates were confirmed by culture on Löwenstein-Jensen (LJ) medium and standard biochemical tests. Drug susceptibility testing of RIF and INH was determined by the proportion method on LJ medium. Mutations conferring resistance to INH and RIF were determined by polymerase chain reaction analysis and sequencing. Results. In this study, 772 (22.68%) MTB strains were isolated from 3,404 TB-suspected patients, of whom 26.6% were women and 73.8% male. Of the 772 clinical strains, 8 (1.03%) were MDR (resistant to INH and RIF), 15 (1.94%) were resistant to RIF and 4 (0.5%) were resistant to INH. Of the 12 identified isolates identified (including both 4 isolates resistant to INH and 8 isolates resistant to MDR), 2 (16.6%) had a mutation at codon 315 of katG, 1 (8.33%) had a mutation at (-15) of inhA, and 9 (75%) did not show a detectable mutation. Regarding rifampin, the frequency of mutations in the rpoB gene was the following: codons 531 (n=7, 30.4%), 533 (n=5, 21.7%), 526 (n = 2, 8.69%) and 511 (n=1, 4.3%). Furthermore, no mutations were detected in 8 (34.7%) isolates. Conclusion. The most prevalent mutation in INH resistant isolates was at codon 315 of katG. In RIF-resiatant isolates, the most prevalent mutation was at codon 531 of the rpoB gene. In a considerable number of isolates, no mutations in katG, inhA, and rpoB were found compared with deposited sequences available from NCBI GenBank.