Effects of cinnamon essential oil on quorum-sensing-associated virulence and biofilm formation in <i>Pseudomonas tolaasii</i>

Cinnamon essential oil (CEO), one of volatile plant compounds, exhibits potent inhibitory effects on bacterial growth. Pseudomonas tolaasii (P. tolaasii) is the primary spoilage bacterium that causes the decay of Agaricus bisporus. This study investigated the effects of cinnamon essential oil (CEO) on quorum sensing (QS) and biofilm formation in Pseudomonas tolaasii. Whole-genome analysis revealed 102 QS-related genes and their association with 10 virulence protein clusters. AHL signaling molecules (C4-HSL, C6-HSL, C8-HSL, and 3-Oxo-C10-HSL) were identified using biosensor methods and LC-MS/MS. CEO significantly inhibited virulence factor secretion, including protease, elastase, and rhamnolipid. It also reduced swarming and swimming motility by 77.21% and 71.38%, respectively, and effectively suppressed biofilm formation by lowering bacterial viscosity and surface hydrophobicity. At a concentration of 0.4 μL/mL, CEO reduced biofilm formation by 40.89% within 24 h, as measured by the crystal violet method. Microscopic and FTIR analysis confirmed CEO's effect on biofilm and extracellular polymer secretion. Thus, it may serve as a novel type of anti-biofilm agent.