title: Mycobacterium tuberculosis embB codon 306 mutations confer moderately increased resistance to ethambutol in vitro and in vivo.
abstract: Ethambutol (EMB) is a major component of the first-line therapy of tuberculosis. Mutations in codon 306 of embB (embB306) were suggested as a major resistance mechanism in clinical isolates. To directly analyze the impact of individual embB306 mutations on EMB resistance, we used allelic exchange experiments to generate embB306 mutants of M. tuberculosis H37Rv. The level of EMB resistance conferred by particular mutations was measured in vitro and in vivo after EMB therapy by daily gavage in a mouse model of aerogenic tuberculosis. The wild-type embB306 ATG codon was replaced by embB306 ATC, ATA, or GTG, respectively. All of the obtained embB306 mutants exhibited a 2- to 4-fold increase in EMB MIC compared to the wild-type H37Rv. In vivo, the one selected embB306 GTG mutant required a higher dose of ethambutol to restrict its growth in the lung compared to wild-type H37Rv. These experiments demonstrate that embB306 point mutations enhance the EMB MIC in vitro to a moderate, but significant extent, and reduce the efficacy of EMB treatment in the animal model. We propose that conventional EMB susceptibility testing, in combination with embB306 genotyping, may guide dose adjustment to avoid clinical treatment failure in these low-level resistant strains.
authors: Molecular Mycobacteriology Group, National Reference Center for Mycobacteria, Forschungszentrum Borstel, Parkallee 1-40, 23845 Borstel, Germany.
authors: Claudia
authors: C
authors: Plinke
authors: Kerstin
authors: K
authors: Walter
authors: Sahar
authors: S
authors: Aly
authors: Stefan
authors: S
authors: Ehlers
authors: Stefan
authors: S
authors: Niemann
mesh_terms: D000818:Animals; D000995:Antitubercular Agents / Q000494:pharmacology*; D003062:Codon; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D004977:Ethambutol / Q000494:pharmacology*; D005260:Female; D006867:Hydrolases / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics; D010430:Pentosyltransferases / Q000235:genetics*
chemical_list: D000995:Antitubercular Agents; D003062:Codon; D004977:Ethambutol; C540269:EmbB protein, Mycobacterium tuberculosis; D010430:Pentosyltransferases; D006867:Hydrolases; C527647:HsaD protein, Mycobacterium tuberculosis