Decreased susceptibility to azithromycin and erythromycin mediated by a novel mtr(R) promoter mutation in Neisseria gonorrhoeae

During a screen of Neisseria gonorrhoeae clinical isolates obtained in Uruguay for susceptibility to azithromycin, we noticed that approximately 10% of the strains examined displayed decreased susceptibility to azithromycin and erythromycin due to the mtr(CDE)-encoded afflux pump system, but remained susceptible to Triton X-100, We now report that the mtr(R) promoter region of one of these isolates contains a dinucleotide insertion (TT) that mediates this resistance phenotype.