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

Abstract

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 efflux 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.

The Role of the Transcription Factors MtrR and MtrA in the Fitness of the Pathogen Neisseria gonorrhoeae

“…Structural mutations include truncations of the mtrR gene (85) or amino acid substitutions within the theoretical DNA binding domain of the MtrR protein (38,69,107,113,118,174,182,184). Two key promoter mutations have also been described; one is the insertion of a Correia element in the MtrR binding site (85,118), and the other an insertion or deletion of one or two thymidines within the pseudo-inverted repeat of the MtrR binding site (34,38,104,130,184,210,211). The +/-T promoter mutations in particular are frequently isolated and known to cause a greater derepression state of the mtrCDE operon than structural mtrR mutants (65,174).…”

“…This region was further described as the transcriptional start for both the mtrR gene and the mtrCDE operon, and the single base pair change both stopped transcription of the mtrR gene and increased transcription of the mtrCDE operon. This single base pair change is the most commonly described mutation that yields the mtr phenotype (65,113,115,118,194,210,211).…”

“…This deletion is frequently found in clinical isolates and confers greater resistance to hydrophobic agents and higher levels of mtrCDE transcription than that conferred by mutations in the mtrR-coding sequence (64,103,211 mtrA Mutants are Attenuated in vivo: We also compared the relative fitness of wild type gonococci and the mtrA mutant JF3, which is incapable of inducing expression of mtrCDE through the action of the MtrA activator protein (162). JF3 bacteria showed no fitness difference compared to wild type FA19Sm R gonococci in vitro (Fig.…”

“…The most common mutation is a single base pair deletion located in the inverted repeat that acts as the shared but divergent promoter regions of mtrR and mtrCDE (34,38,104,130,184,210,211). Other commonly described mutations are located in the structural gene of mtrR, and include a G45D mutation (38,174,184,198,210) and an A39T mutation (38), which are found in the Here we compared five different mtrR mutations that were isolated clinically or from experimentally infected mice to determine if they confer differential levels of mtrCDE operon derepression as measured by levels of RNA transcript, protein production, antibiotic resistance, and in vivo fitness.…”

“…Phenotypically, these strains exhibit increased levels of resistance to MtrCMtrD-MtrE efflux pump substrates Triton X-lOO (TX-lOO), erythromycin (Em), and azithromycin (Az) (140). A series of publications that detailed the presence of naturally occurring mtr mutants in clinical isolates suggested a fitness benefit or selective factor present in nature that allows for natural mtr mutants to flourish (34,113,118,126,130,184,198,205,210,211). Consistent with these findings, previous work from this lab showed that the mtr phenotype conveys a fitness increase in the murine model of lower genital tract infection (Warner et al, 2007).…”