Combined Effects of Quercetagetin and D-Amino Acids against Pseudomonas aeruginosa: Anti-Quorum Sensing, Antibacterial, and Antibiofilm activities

Pseudomonas aeruginosa , a significant opportunistic pathogen, poses a serious threat to food safety due to its antibiotic resistance and strong biofilm-forming ability. In this study, quercetagetin (Que) was identified as a novel quorum sensing (QS) inhibitor. Reporter strain assays, molecular docking, and dynamic simulation indicated that Que acts as an antagonist of the QS receptors. Que attenuated QS-regulated virulence phenotypes in a dose-dependent manner but showed insufficient antibiofilm activity ( p >0.05) at sub-minimum inhibitory concentration (sub-MIC) levels. In contrast, the combination of 0.5 mmol/L Que with 20 mmol/L D-leucine or D-tryptophan exhibited additive effects on planktonic cells, reducing its survival by 2.19–3.97 log compared to the control. For biofilm cells, the combined treatment potentiated the reduction in cell density by 0.48–1.42 log. Notably, these effects were strain-dependent but were equal to or outperformed those of the ε-polylysine (ε-PL) control. Mechanistically, this enhancement was driven by the disruption of biofilm matrix and cell membrane integrity. This was evidenced by the greater suppression of Acyl-homoserine lactones (AHLs) synthesis and virulence phenotypes, alongside substantial reductions in biofilm biomass and roughness and increased in membrane permeability compared to Que. Furthermore, the combination resulted in repression of key enzymes activities (Na + -K + -ATPase and succinate dehydrogenase) by 29%–38%. These changes indicated a promising strategy to control P. aeruginosa and enhance food safety.