Interspecies Outer Membrane Vesicles (OMVs) Modulate the Sensitivity of Pathogenic Bacteria and Pathogenic Yeasts to Cationic Peptides and Serum Complement.

Justyna Roszkowiak,Daria Augustyniak,Zuzanna Drulis-Kawa,Andrzej Żak,Grzegorz Guła,Jerzy Gubernator,Paweł Jajor

doi:10.3390/ijms20225577

Abstract

The virulence of bacterial outer membrane vesicles (OMVs) contributes to innate microbial defense. Limited data report their role in interspecies reactions. There are no data about the relevance of OMVs in bacterial-yeast communication. We hypothesized that model Moraxella catarrhalis OMVs may orchestrate the susceptibility of pathogenic bacteria and yeasts to cationic peptides (polymyxin B) and serum complement. Using growth kinetic curve and time-kill assay we found that OMVs protect Candida albicans against polymyxin B-dependent fungicidal action in combination with fluconazole. We showed that OMVs preserve the virulent filamentous phenotype of yeasts in the presence of both antifungal drugs. We demonstrated that bacteria including Haemophilus influenza, Acinetobacter baumannii, and Pseudomonas aeruginosa coincubated with OMVs are protected against membrane targeting agents. The high susceptibility of OMV-associated bacteria to polymyxin B excluded the direct way of protection, suggesting rather the fusion mechanisms. High-performance liquid chromatography-ultraviolet spectroscopy (HPLC-UV) and zeta-potential measurement revealed a high sequestration capacity (up to 95%) of OMVs against model cationic peptide accompanied by an increase in surface electrical charge. We presented the first experimental evidence that bacterial OMVs by sequestering of cationic peptides may protect pathogenic yeast against combined action of antifungal drugs. Our findings identify OMVs as important inter-kingdom players.

Highlights

In the environment, different microbial populations, including bacteria and fungi, co-exist
Bacteria can release outer membrane vesicles (OMVs) that act as extracellular decoys for some antimicrobials
We report that OMVs may serve as a model of passive interspecies protection of prominent pathogenic bacteria and pathogenic yeasts

Summary

Introduction

Different microbial populations, including bacteria and fungi, co-exist. Understanding which factors may be potentially important players in interspecies dynamics of growth and to what degree these dynamics are mediated by the host is very important Among these factors are outer membrane vesicles (OMVs) of Gram-negative bacteria classified recently as secretion system type zero [1]. These proteoliposomal nanoparticles released from the cell play an important role in bacterial physiology and pathogenesis. We used our well-characterized OMVs from Moraxella catarrhalis Mc6 [4,21] as model vesicles and characterized their protective potential against model membrane-active agents in various interspecies combinations. We investigated whether OMVs-dependent protection is a signature of only free vesicles or those associated with the cell

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