Propolis Affects Pseudomonas aeruginosa Growth, Biofilm Formation, eDNA Release and Phenazine Production: Potential Involvement of Polyphenols.

Aida Meto,Agron Meto,Stefania Benvenuti,Giorgia Boaretto,Federica Pellati,Diego Pinetti,Bruna Colombari,Elisabetta Blasi,Lucia Marchetti

doi:10.3390/microorganisms8020243

Abstract

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic pathogen responsible for a wide range of clinical conditions, from mild infections to life-threatening nosocomial biofilm-associated diseases, which are particularly severe in susceptible individuals. The aim of this in vitro study was to assess the effects of an Albanian propolis on several virulence-related factors of P. aeruginosa, such as growth ability, biofilm formation, extracellular DNA (eDNA) release and phenazine production. To this end, propolis was processed using three different solvents and the extracted polyphenolic compounds were identified by means of high performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS) analysis. As assessed by a bioluminescence-based assay, among the three propolis extracts, the ethanol (EtOH) extract was the most effective in inhibiting both microbial growth and biofilm formation, followed by propylene glycol (PG) and polyethylene glycol 400 (PEG 400) propolis extracts. Furthermore, Pseudomonas exposure to propolis EtOH extract caused a decrease in eDNA release and phenazine production. Finally, caffeic acid phenethyl ester (CAPE) and quercetin decreased upon propolis EtOH extract exposure to bacteria. Overall, our data add new insights on the anti-microbial properties of a natural compound, such as propolis against P. aeruginosa. The potential implications of these findings will be discussed.

Highlights

In nature, many microbial species use a cell-to-cell signaling system, named quorum sensing (QS), to form biofilms on both biotic and abiotic surfaces
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Our study focused on Pseudomonas, as a prototype of a hardly attackable pathogen, capable to express numerous virulence factors; its susceptibly to propolis has been evaluated in terms of variation in growth ability, biofilm formation, production of phenazines and extracellular DNA (eDNA) release

Summary

Introduction

Many microbial species use a cell-to-cell signaling system, named quorum sensing (QS), to form biofilms on both biotic and abiotic surfaces. Microorganisms embedded in a biofilm acquire resistance to drugs and detergents and make host defenses less efficient [1,2,3]. Microbial biofilms consist of sessile cells, embedded in a self-produced matrix of polysaccharides, proteins, lipids and extracellular DNA (eDNA) [4,5]. P. aeruginosa is responsible for oral infections in patients with clinical conditions, such as apical periodontitis, pulp necrosis, pulpitis or mandibular/maxillary alveolitis [7]. The onset and development of infections are mostly related to the well-established ability of P. aeruginosa to produce biofilm, either onto biotic or abiotic surfaces

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