CHARACTERIZATION OF EMBCAB GENE MUTATIONS ASSOCIATED WITH ETHAMBUTOL RESISTANCE IN MYCOBACTERIUM TUBERCULOSIS ISOLATES FROM IRAN

Background and Aim:Ethambutol (EMB) is one of the first line drugs in the standard combination therapy for tuberculosis (TB). As the embCAB operon is considered to be involved in resistance to EMB, this study was aimed to analyze the mutations within embCAB operon among MTB isolates from Iran, to find out a possible association between these mutations and EMB resistance.Methods:A 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 by using sets of primers for various gene loci of embC, embA and emb, followed by sequencing for the detection of most common alterations.Results:In total 10 isolates showed resistance to EMB by phenotypic susceptibility testing (3.25 %). The mutation rate in 10 EMB-resistant MTB strains was 20.0% (n=2), comprises one mutation in embB (10.0%), at codon 306 Met to Val, and one in embC (10.0%), at codon 270 Thr to Ile. A non-synonymous mutation in embA gene in one of the randomly selected EMB susceptible isolates located in codon 330 Lue to Lue were also noticed. The majority of our EMB-resistant isolates (n=8/ 80%) could not be explained by the mutations within embCAB.Conclusion:So, these mutations alone, are not sufficient for the development of full resistance to EMB in MTB isolates. Additional mechanisms of resistance other than mutations within embCAB operon should also be considered.