Polimorfismos genéticos como determinantes de resistência à etionamida em Mycobacterium tuberculosis

Abstract

In Mycobacterium tuberculosis, ethA encodes the enzyme EthA, responsible for the activation of the antimycobacterial drug ethionamide (ETA). Adjacent to ethA, ethR encodes a transcriptional repressor, whose overexpression inhibits transcription of ethA, resulting in high levels of resistance to ETA. Mutations in ethA are associated with resistance to ETA; however, clinical isolates of M. tuberculosis that are resistant to ETA but do not bear mutations in ethA have been described. The role of EthR in the transcriptional control of ethA and the identification of an isolate resistant to ETA but without mutations in this gene (but with a mutation in ethR) suggest that mutations in ethR could be associated with resistance to ETA. Therefore, the goal of this work was to investigate if mutations in ethR could be determinants of resistance to ETA, and to evaluate if the detection of mutations in regions associated with resistance to ETA could complement the results of phenotypical drug susceptibility tests. To do this, 69 M. tuberculosis clinical isolates, from 45 patients that received ETA as part of their treatment, were reactivated from our strain collection at the National Reference Laboratory for Tuberculosis, at the Oswaldo Cruz Foundation. ETA, as well as isoniazid, resistance profiles were determined, and genomic DNA was obtained from all strains. Three genomic regions previously implicated in resistance to ETA (ethA-ethR, the promoter of inhA, and mshA) were then sequenced, to identify mutations that could be associated with the resistance profiles of the isolates studied. It was possible to identify seventeen mutations in these locis, among which twelve could possibly be related to resistance to ETA, three of them already described in the literature. The rapid detection of antimicrobial resistance is a critical factor in the treatment of tuberculosis patients, and is crucial for the control of the transmission of this disease. The results of this study may lead to the identification of molecular markers associated with resistance to ETA. In the future, such markers may be used to determine resistance profiles more quickly than by using phenotypical methods, thereby aiding in the control of tuberculosis.