A Novel Mechanism of High-Level, Broad-Spectrum Antibiotic Resistance Caused by a Single Base Pair Change in Neisseria gonorrhoeae

Abstract

The MtrC-MtrD-MtrE multidrug efflux pump of Neisseria gonorrhoeae confers resistance to a diverse array of antimicrobial agents by transporting these toxic compounds out of the gonococcus. Frequently in gonococcal strains, the expression of the mtrCDE operon is differentially regulated by both a repressor, MtrR, and an activator, MtrA. The mtrR gene lies 250 bp upstream of and is transcribed divergently from the mtrCDE operon. Previous research has shown that mutations in the mtrR coding region and in the mtrR-mtrCDE intergenic region increase levels of gonococcal antibiotic resistance and in vivo fitness. Recently, a C-to-T transition mutation 120 bp upstream of the mtrC start codon, termed mtr120, was identified in strain MS11 and shown to be sufficient to confer high levels of antimicrobial resistance when introduced into strain FA19. Here we report that this mutation results in a consensus −10 element and that its presence generates a novel promoter for mtrCDE transcription. This newly generated promoter was found to be stronger than the wild-type promoter and does not appear to be subject to MtrR repression or MtrA activation. Although rare, the mtr120 mutation was identified in an additional clinical isolate during sequence analysis of antibiotic-resistant strains cultured from patients with gonococcal infections. We propose that cis-acting mutations can develop in gonococci that significantly alter the regulation of the mtrCDE operon and result in increased resistance to antimicrobials.

High-Level Cefixime- and Ceftriaxone-Resistant Neisseria gonorrhoeae in France: Novel penA Mosaic Allele in a Successful International Clone Causes Treatment Failure

“…2). Thus, WHO L may harbor factor X, i.e., the nontransformable determinant that remains to be identified (12,21,27,34,43,58), and it cannot be excluded that the cefixime and ceftriaxone MICs are also enhanced by the mtr 120 mutation in WHO L (26).…”

The Challenge of Efflux-Mediated Antibiotic Resistance in Gram-Negative Bacteria

“…This induction is also dependent on an envelope protein, MtrF, whose expression is negatively controlled by MtrR and MpeR (16,869). A single-base-pair change located 120 bp upstream of the mtrC start codon generates a second promoter for mtrCDE expression and is sufficient not only to increase mtrCDE expression but also to render such expression independent of the control by MtrR or MtrA (870).…”

Antimicrobial Resistance in Neisseria gonorrhoeae in the 21st Century: Past, Evolution, and Future

“…In addition to these target modifications, as for penicillin (see above), an increased efflux and decreased influx of tetracycline, due to the mtrR resistance determinant (197)(198)(199) and penB resistance determinants (199)(200)(201), respectively, result in an enhanced resistance to tetracycline.…”

“…Furthermore, penicillin MICs can be increased further by specific mutations resulting in increased efflux by overexpression of the MtrCDE efflux pump system, which exports the penicillin out of the cell (mtrR resistance determinant) (3)(4)(5)(197)(198)(199), and by mutations resulting in a decreased influx (intake) of penicillin, through a decreased permeability of the outer membrane channel porin PorB1b (penB resistance determinants) (3)(4)(5)(199)(200)(201). In laboratory isolates, specific mutations in pilQ (encoding loss-offunction alterations, e.g., E666K, in the pore-forming secretin PilQ of type IV pili) are also found in strains with high-level resistance to penicillin that contain alterations of penA, mtrR, and penB (5,187,199,202).…”