Ultrasound-assisted nanoemulsions from Foeniculum vulgare: antimicrobial activity, anti-biofilm, and anti-virulence in Pseudomonas aeruginosa

This study investigated ultrasound-assisted nanoemulsions of Foeniculum vulgare essential oil (FEO-NEs) and their antimicrobial and anti-virulence activity against two Pseudomonas aeruginosa strains, with validation in a food model. Ultrasonication reduced droplet size from 1332.43 nm to 231.37 and 219.48 nm after 5 and 10 min, respectively, generating homogeneous nanoemulsions with low polydispersity (PDI 0.29) and zeta potential values from -25.51 to -33.58 mV. Nanoemulsification enhanced antibacterial efficacy, reducing the MIC of free oil (50 mg/mL) to strain-dependent values of 1.56 and 12.5 mg/mL. Time-kill assays showed concentration-dependent reductions of up to 4 log CFU/mL within 8 h at 2× MIC, consistent with membrane damage and leakage of intracellular constituents. FEO-NEs significantly reduced swimming motility, decreased preformed biofilm biomass by up to 99.83%, and lowered pyocyanin production from 9.59 to 10.41 to 5.72-6.85 μg/mL, indicating attenuation of virulence-associated phenotypes. Antimicrobial activity was maintained up to 100 °C during thermal treatment. In carrots stored at 4 °C, FEO-NEs reduced P. aeruginosa populations from approximately 5.5-6.8 to 1.0-1.7 log CFU over 15 days. These findings demonstrate that nanoemulsification improved both antimicrobial efficacy and virulence attenuation of fennel essential oil, supporting its potential for controlling Pseudomonas in minimally processed foods.