Pseudomonas aeruginosamexR and mexEF Antibiotic Efflux Pump Variants Exhibit Increased Virulence.

Mylene Vaillancourt,Peter Jorth,Catherine Bresee,Rahgavi Poopalarajah,Sam P Limsuwannarot

doi:10.3390/antibiotics10101164

Mylene Vaillancourt, Peter Jorth + Show 3 more

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https://doi.org/10.3390/antibiotics10101164

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Abstract

Antibiotic-resistant Pseudomonas aeruginosa infections are the primary cause of mortality in people with cystic fibrosis (CF). Yet, it has only recently become appreciated that resistance mutations can also increase P. aeruginosa virulence, even in the absence of antibiotics. Moreover, the mechanisms by which resistance mutations increase virulence are poorly understood. In this study we tested the hypothesis that mutations affecting efflux pumps can directly increase P. aeruginosa virulence. Using genetics, physiological assays, and model infections, we show that efflux pump mutations can increase virulence. Mutations of the mexEF efflux pump system increased swarming, rhamnolipid production, and lethality in a mouse infection model, while mutations in mexR that increased expression of the mexAB-oprM efflux system increased virulence during an acute murine lung infection without affecting swarming or rhamnolipid gene expression. Finally, we show that an efflux pump inhibitor, which represents a proposed novel treatment approach for P. aeruginosa, increased rhamnolipid gene expression in a dose-dependent manner. This finding is important because rhamnolipids are key virulence factors involved in dissemination through epithelial barriers and cause neutrophil necrosis. Together, these data show how current and proposed future anti-Pseudomonal treatments may unintentionally make infections worse by increasing virulence. Therefore, treatments that target efflux should be pursued with caution.

Highlights

Deletions in both WT PAO1 and in PAO1-AzEvB8, and the PAO1-AzEvB8 ∆mexAB strain was susceptible to aztreonam by a gradient diffusion assay as the PAO1 ∆mexAB
Strain (Figure 1A); the mode minimum inhibitory concentrations (MIC) for ∆mexAB strains was 0.19 μg/mL, compared to 16 μg/mL for PAO1-AzEvB8 and 1.0 μg/mL for WT PAO1. This showed that mexAB was required for aztreonam resistance of the of the PAO1-AzEvB8 mutant
We showed that two different mutations affecting efflux pumps that evolved in response to aztreonam selective pressure can increase P. aeruginosa virulence in the ab

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium that colonizes a wide range of environments [1]. This environmental flexibility is due to its high adaptability to changing conditions and is driven by substantial metabolic versatility, expression of a large array of virulence factors, and extensive adaptive transport and efflux systems [2]. P. aeruginosa is infamous for causing serious nosocomial infections, such as burn wound infections and ventilator-associated pneumonia [3], and it is the predominant pathogen causing chronic infections in cystic fibrosis (CF) [4]

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