<p>Characterization of the most common <em>embCAB</em> gene mutations associated with ethambutol resistance in <em>Mycobacterium tuberculosis</em> isolates from Iran</p>

Abstract

IntroductionEthambutol (Emb) is one of the first-line drugs in the standard combination therapy for tuberculosis; however, due to the rapid increase in Emb resistance among clinical isolates of Mycobacterium tuberculosis (MTB), early detection of Emb resistance is desirable. As the embCAB operon is considered involved in resistance to Emb, this study aimed to analyze the most common mutations within the embCAB operon among MTB isolates from Iran to find any correlations of these mutations with Emb resistance.MethodsA total of 307 clinical isolates of MTB were screened for Emb resistance by phenotypic drug-susceptibility testing. PCR amplification was performed on extracted DNA from all Emb-resistant and randomly selected Emb-susceptible isolates using sets of primers for various gene loci of embC, embA, and embB, followed by sequencing for the detection of most common alterations.ResultsIn total, ten isolates showed resistance to Emb by phenotypic susceptibility testing (3.25%). The mutation rate in ten Emb-resistant MTB strains was 20% (n=2), comprising one mutation in embB (10%), at codon 306 Met–Val and one in embC (10%) at codon 270 Thr–Ile. A nonsynonymous mutation in the embA gene in one of the randomly selected Emb-susceptible isolates located in codon 330 Leu–Leu was also noticed.ConclusionThe majority of our Emb-resistant isolates (n=8, 80%) did not demonstrate the sequences investigated within the embCAB operon. As such, these mutations solely are insufficient for the development of complete resistance to Emb in MTB isolates. Additional mechanisms of resistance other than mutations in these sequences studied within the embCAB operon should also be considered.

Whole Genome Sequencing Results Associated with Minimum Inhibitory Concentrations of 14 Anti-Tuberculosis Drugs among Rifampicin-Resistant Isolates of Mycobacterium Tuberculosis from Iran

“…Ethambutol resistance was mostly linked to the mutations within the embB gene (codon 306 as the dominant position), but not embA. Khosravi et al reported embA mutation from EMB-susceptible strains [47]. Additionally, Sun et al revealed that 82.6% of EMB-resistant isolates from China had at least a mutation in the embABC locus, but contrary to this study, they were located mostly in the embA and embB upstream region [48].…”

Evaluation of Whole-Genome Sequence Method to Diagnose Resistance of 13 Anti-tuberculosis Drugs and Characterize Resistance Genes in Clinical Multi-Drug Resistance Mycobacterium tuberculosis Isolates From China

“…In order to find new possible resistance-related mutations, we further analyzed all mutations in genes above and another 15 resistance-related genes for INH ( nat, ndh, iniA, iniB , and iniC ), PZA ( rpsA and panD ), EMB ( embC, embR , and ubiA ), SM ( gidB ), and CLO resistance ( rv1979c, rv2535c, mmpL3 , and mmpL5 ) (Table S1) (Wong et al, 2011; Zhang et al, 2013, 2015a; Hartkoorn et al, 2014; Shi et al, 2014; Vilchèze and Jacobs, 2014; Almeida et al, 2016; Li et al, 2017; Ismail et al, 2018; Sun et al, 2018; Khosravi et al, 2019; Tulyaprawat et al, 2019).…”

Frequency of Codon 306 Mutations in embB Gene of Mycobacterium tuberculosis Resistant to Ethambutol: A Systematic Review and Meta-Analysis

“…PCR showed that the mutation rate in 10 EMB-resistant TB strains was 20% (10% mutation in embB codon 306 Met–Val and 10% in embC codon 270 Thr–Ile). [ 59 ] According to other research studies in Iran that were performed in 2015, the prevalence of TB was 66.4%, among which 7% had extrapulmonary TB. [ 60 ] Efficiency of the Bacillus Calmette-Guerin (BCG) vaccine has been proved, but the type, dose, and strength of the vaccine strain, age, and inoculation technique are different and cause Mendelian susceptibility to mycobacterial disease (MSMD) primary immunodeficiency (PID).…”