Modulation of Pseudomonas aeruginosa Quorum Sensing and Biofilm Formation by Quercetin Extracted from Pleurotus ostreatus

Background: Pseudomonas aeruginosa relies on quorum sensing (QS) to regulate virulence, biofilm formation, and antimicrobial tolerance, making QS inhibition (QSI) an attractive antivirulence strategy. Quercetin is a known QSI-active flavonoid, but its potential as a mushroom-derived therapeutic agent remains underexplored. Methods: Quercetin was extracted from P. ostreatus and evaluated alongside purified quercetin using GFP-based QS reporter assays (lasB-gfp and pqsA-gfp), biofilm assays, protease activity assays, and molecular docking against LasR, PqsR, and PqsE. Results: Both treatments significantly reduced lasB- and pqsA-driven GFP reporter activity at sub-inhibitory concentrations (10– 100 μM) that did not affect bacterial growth or viability. Inhibition was dose-dependent and more pronounced for the PQS system, accompanied by substantial reductions in extracellular protease activity and strong suppression of biofilm formation and partial dispersal of established biofilms. Molecular docking revealed favourable binding of quercetin to the QS regulators LasR and PqsR, with high-affinity interaction in the PqsR co-inducer pocket, while binding to PqsE was weak and non-specific. Conclusion: These mechanistic insights align with the observed preferential PQS inhibition. The P. ostreatus quercetin-extract closely matched the potency of pure quercetin across all assays, confirming effective extraction and stability. This positions mushroom-derived quercetin as a sustainable, natural QSI capable of attenuating key virulence pathways in P. aeruginosa . This work supports the development of quercetin-rich P. ostreatus extracts as promising adjunctive therapies for managing chronic, biofilm-associated infections..