Inhibition of Pseudomonas aeruginosa quorum sensing-regulated behaviors by mushroom extracts

Microbial biofilm formation, a quorum sensing (QS) phenomenon based on cell-to-cell communication through ligand-receptor interactions, is one of the major causes of nosocomial and chronic infections, foodborne diseases and associated deaths. Its inhibition is therefore considered a promising approach to fight infections. In this context, Cantharellus cibarius, Trametes versicolor, Lentinula edodes and Pleurotus ostreatus, ethno-medicinal and culinary mushrooms, have been investigated as an antibiofilm and anti-QS agents against Pseudomonas aeruginosa.

The aim of this study was to identify the most effective solvent system for the extraction of bioactive compounds from medicinal mushrooms with antivirulence activity against P. aeruginosa and to elucidate the potential molecular mechanism. In addition, this work aims to address the urgent need for novel, non-antibiotic strategies to combat multidrug-resistant (MDR) pathogens.

Fluorescence microscopy (FM), scanning electron microscopy (SEM) and quantitative real-time PCR were employed to explore the antibiofilm and anti-QS potential of mushroom extracts. Chemical characterization of the extracts was performed using Uv-Vis, FTIR and UHPLC Q-ToF MS, while their toxicity was evaluated in an in vivo model using Caenorhabditis elegans.

Hot alkali polysaccharide extracts (APE) were the most effective, as they significantly decreased the mRNA levels of all tested QS, especially genes encoding autoinducer synthases (lasI, rhlI and pqsA), by 2- to 17-fold, as well as virulence factor genes of P. aeruginosa. Furthermore, micrographs (FM and SEM) confirmed that all APEs significantly inhibited adhesion and biofilm formation. FTIR and UV-Vis analyses showed that the extracts consisted mainly of polysaccharides, while UHPLC Q-ToF MS analysis revealed the presence of azelaic acid and vanillylacetone in all extracts. The in silico studies showed that vanillylacetone strongly interferes with various QS receptors (LasR, PqsR and RhlR) and could serve as a competitive inhibitor for the autoinducer molecules and possibly induce conformational changes in proteins. APE has also been found to increase the antibacterial efficacy of antibiotics. In vivo toxicity assays with C. elegans demonstrated their safety (with a survival rate of ≥90 %).

The tested mushrooms are promising sources of safe, natural antibiofilm and antivirulence agents, justifying their traditional use in infection control and offering potential for novel anti-infective therapies.