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Target (MexB) and efflux based mechanisms decreasing the effectiveness of the efflux pump inhibitor D13-9001 in P. aeruginosa PAO1: uncovering a new role for MexMN-OprM in efflux of β-lactams and a novel regulatory circuit controlling MexMN expression

Ranjitkar, Srijan and Jones, Adriana and Mostafavi, Mina and Zwirko, Zachary and Iartchouk, Oleg and Barnes, Whitney and Walker, John and Willis, Thomas and Lee, Patrick and Dean, Charles (2019) Target (MexB) and efflux based mechanisms decreasing the effectiveness of the efflux pump inhibitor D13-9001 in P. aeruginosa PAO1: uncovering a new role for MexMN-OprM in efflux of β-lactams and a novel regulatory circuit controlling MexMN expression. Antimicrobial agents and chemotherapy, 63 (2). pp. 1-14. ISSN 1098-6596; 0066-4804

Abstract

Efflux pumps contribute to antibiotic resistance in Gram-negative pathogens.
Correspondingly, efflux pump inhibitors (EPIs) may reverse this resistance. D13-
9001 specifically inhibits MexAB-OprM in Pseudomonas aeruginosa. Mutants with decreased
susceptibility to MexAB-OprM inhibition by D13-9001 were identified, and these
fell into two categories: those with alterations in the target MexB (F628L and ΔV177)
and those with an alteration in a putative sensor kinase of unknown function, PA1438
(L172P). The alterations in MexB were consistent with reported structural studies of the
D13-9001 interaction with MexB. The PA1438L172P alteration mediated a �150-fold upregulation
of MexMN pump gene expression and a �50-fold upregulation of PA1438
and the neighboring response regulator gene, PA1437. We propose that these be renamed
mmnR and mmnS for MexMN regulator and MexMN sensor, respectively. MexMN
was shown to partner with the outer membrane channel protein OprM and to pump
several �-lactams, monobactams, and tazobactam. Upregulated MexMN functionally replaced
MexAB-OprM to efflux these compounds but was insusceptible to inhibition by
D13-9001. MmnSL172P also mediated a decrease in susceptibility to imipenem and biapenem
that was independent of MexMN-OprM. Expression of oprD, encoding the uptake
channel for these compounds, was downregulated, suggesting that this channel is also
part of the MmnSR regulon. Transcriptome sequencing (RNA-seq) of cells encoding
MmnSL172P revealed, among other things, an interrelationship between the regulation of
mexMN and genes involved in heavy metal resistance.

Item Type: Article
Date Deposited: 12 Feb 2019 00:45
Last Modified: 12 Feb 2019 00:45
URI: https://oak.novartis.com/id/eprint/36900

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