Synergistic antimicrobial strategies: Quorum sensing inhibitors combined with conventional antibiotics for combating Pseudomonas aeruginosa infections.

Pseudomonas aeruginosa is a widely prevalent multidrug-resistant pathogen in clinical environments, capable of forming biofilms and evading antibiotic clearance, which poses a significant threat to public health. Targeting the multidrug resistance and biofilm formation mechanisms of P. aeruginosa, this study designed and synthesized a series of novel N-acyl homoserine lactone (AHL)-based quorum sensing inhibitors (QSIs). Through structure-activity relationship optimization and activity screening, compound 5-6 was identified as a lead molecule. By competitively binding to the LasR protein receptor (binding free energy: 8.9 kcal/mol), it significantly inhibited biofilm formation (inhibition rate: 44.6 ± 2.5%) and the secretion of virulence factors (e.g., inhibition rate of the representative virulence factor pyocyanin: 97.8 ± 2.5%). Using a synergistic antimicrobial assay model, co-administration of compound 5-6 with fluoroquinolones or tetracyclines reduced their minimum inhibitory concentrations (MICs) by 75% and 50%, respectively. Additionally, the spatiotemporal bactericidal model validated that compound 5-6 assisted in shortening the bacterial clearance time by 1-2 h when combined with high-concentration antibiotics. Mechanistically, compound 5-6 induces RNA leakage via dynamic membrane disruption, further inhibits extracellular polymeric substance (EPS) assembly, and continuously suppresses biofilm regenerative capacity, thereby achieving a dual synergistic strategy of "Defense Weakening-Antibiotic Potentiation." This research provides a novel adjuvant treatment regimen for clinical refractory Gram-negative bacterial infections.