RESUMO
Purpose: The presence of embB306 mutation in ethambutol (EMB)‑susceptible (EMBs) clinical isolates questions the significance of these mutations in conferring resistance to EMB. The present study was carried out to determine the occurrence of embB306 mutation in EMB‑resistant (EMBr) and EMBs strains of M. tuberculosis. One hundred and four multidrug‑resistant tuberculosis (MDR‑TB) strains were also included to establish the relevance of excessive use of rifampicin (RIF) and isoniazid (INH) in occurrence of embB306 mutations in EMBs M. tuberculosis isolates. Materials and Methods: Deoxyribonucleic acid (DNA) from M. tuberculosis clinical strains was isolated by cetyltrimethylammonium bromide (CTAB) method. Phenotypic and genotypic drug susceptibility testing (DST) was performed on 354 M. tuberculosis isolates by using standard proportion method and multiplex‑allele‑specific polymerase chain reaction assay, respectively. Results: The overall frequency of embB306 mutations in EMBr isolates was found to be five times higher than its occurrence in EMB‑susceptible isolates (50% vs 10%). Further, the association between embB306 mutation and EMB‑resistance was observed to be statistically significant (P = 0.000). Conclusion: The embB306 is not only the main causative mutation of EMB resistance, but is a sensitive applicant marker for EMB‑resistance study.