Frequency of mutational changes in the embB among the ethambutol-resistant strains of Mycobacterium tuberculosis in Iran

Abstract

Introduction: Early detection of drug resistant tuberculosis is one of the main priorities of TB control program. Ethambutol (EMB) is a firstline anti-TB drug that is effective for preventing treatment failures caused by Mycobacterium tuberculosis strains that are resistant to other drugs. The aim of this study was to sequence the embB gene to characterize the mutations causing resistance to EMB and to analyze the relationship between bacterial genotype and EMB resistance among M. tuberculosis isolates in Iran. Methodology: A total of 20 M. tuberculosis isolates comprising 10 multidrug-resistant (MDR) and 10 non-MDR isolates, recovered from TB patients in four regions: Tehran, Isfahan, Zahedan, Khorasan, were analyzed. Mutational profiling was performed by amplifying and sequencing the embB gene. Spoligotyping was carried out to characterize the bacterial genotype. Results: Phenotypic EMB resistance was found in 13 strains. Mutations affecting ethambutol resistance-determining region (ERDR) of the embB were identified in 6 of 13 EMB-resistant isolates. The majority of these mutations resulted in amino acid substitution at position 306 (M306V). A novel mutation at codon 366 was identified (S366L) in one isolate. Ural was the most predominant genotype in the studied population. Beijing genotype was associated with both MDR and EMB resistance in which all mutations occurred at codon 306 of the embB gene. Conclusion: A significant association between Beijing genotype and EMB resistance was found, mainly due to mutations at embB306. Results of this study can be used as a basis to develop or improve rapid molecular tests to monitor drug-resistant strains in this country.

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

“…The discordance between phenotypic AST of Emb and mutations in the embCAB operon has also been reported by investigators from other countries and Iran 31–33. In the study from Iran, embB mutations were investigated in a few Iranian cities, and based on their results from four Emb-resistant isolates recovered from Tehran, only one 306 mutation was detected, and in some cities no 306 mutation was demonstrated among the phenotypic Emb-resistant isolates 33. In the current study, we investigated the most common mutation sites within the three genes embA, embB , and embC .…”

“…Among the Emb phenotypic resistant isolates, only two were detected by mutations within the embCAB operon. The discordance between phenotypic AST of Emb and mutations in the embCAB operon has also been reported by investigators from other countries and Iran 31–33. In the study from Iran, embB mutations were investigated in a few Iranian cities, and based on their results from four Emb-resistant isolates recovered from Tehran, only one 306 mutation was detected, and in some cities no 306 mutation was demonstrated among the phenotypic Emb-resistant isolates 33.…”

Identification of mutations in rpoB, pncA, embB, and ubiA genes among drug-resistant Mycobacterium tuberculosis clinical isolates from Iran

“…Nevertheless, other studies also found discord between phenotypic resistance assays and genotypic changes in the embCAB operon [50]. EmbB mutations were also detected in 5% of phenotypically EMB s isolates which varied from 14.3 [54] to 45% [8] in previous studies. Earlier studies did not report the A346P substitution in EMB s isolates.…”