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 Urug uay for susceptibility to azithromycin, we noticed that approximately 10% o f the strains examined displayed decreased susceptibility to azithromycin a nd erythromycin due to the mtr(CDE)-encoded afflux pump system, but remaine d susceptible to Triton X-100, We now report that the mtr(R) promoter regio n of one of these isolates contains a dinucleotide insertion (TT) that medi ates this resistance phenotype.