The aim of this study was to characterize the most frequent mutations associated with rifampicin (RIF) and isoniazid (INH) resistance of Mycobacterium tuberculosis isolates from Ecuador. Sequence analysis of 40 strains, resistant for the tuberculosis drugs INH, RIF, or for both showed that of the 31 strains with resistance to INH, 20 strains (64.5%) carried a mutation in the katG gene (codon 315). Eight INH-resistant strains carried a mutation in the katG gene at codon 463. This katG463 mutation, considered a phylogenetic marker, was exclusively found in INH-resistant strains and not in 121 INH-susceptible strains. Of the 35 strains resistant to RIF, 33 (93.9%) had mutations in the hot spot region of the rpoB gene, predominantly in codons 531, 516, and 526. Our results show that sequence-based detection for drug resistance of the katG will identify, respectively, 64.5% or, considering katG463 as a marker, 90.3% of the INH-resistant strains. Sequencing of the hot spot region of the rpoB gene will detect 94.3% of the RIF drug-resistant isolates in Ecuador. This is appropriate for fast screening for drug resistance with the GeneXpert MTB/RIF assay or by direct sequencing of a part of the genes katG and rpoB of PCR products obtained from DNA isolation from primary cultures.
Keywords: Ecuador; isoniazid; rifampicin.