Synergistic Antibacterial Activity of Quercetin-Functionalized Magnetic Nanoparticles Combined with Ciprofloxacin on Pathogenic Pseudomonas Aeruginosa Via Targeting Virulence, Efflux Pump, and Adhesion-Associated Genes and Molecular Docking Analysis.

Biofilm formation and the activity of efflux pumps are major contributors to antibiotic resistance in clinical strains of Pseudomonas aeruginosa and significantly enhance the pathogenicity of this bacterium. Functionalization of metal nanoparticles with plant-derived flavonoids, particularly when combined with conventional antibiotics, represents a promising strategy for overcoming antimicrobial resistance. In the present study, we investigated the synergistic inhibitory effects of quercetin-functionalized magnetic nanoparticles (Fe3O4@SiPr@Quercetin NPs) in combination with ciprofloxacin against ciprofloxacin-resistant clinical isolates of P. aeruginosa. Ciprofloxacin-resistant isolates were collected from hospitals and diagnostic laboratories in Tehran Province, Iran. The synthesized nanoparticles exhibited a spherical morphology with an average diameter of 165 nm. Synergistic antibacterial activity of the functionalized nanoparticles combined with ciprofloxacin was evaluated using the checkerboard assay. The most pronounced reduction in biofilm formation, was observed in strains treated with the nanoparticle-ciprofloxacin combination, with inhibition rates ranging from 18.9 ± 1.13% to 90.05 ± 5.72%. Time-kill curve analysis further demonstrated that Fe3O4@SiPr@Quercetin in combination with ciprofloxacin produced a more rapid bactericidal effect, reducing bacterial counts to 5.87-4.72 log CFU/mL after 8 h of treatment. Moreover, quantitative real-time PCR (qPCR) analysis revealed significant downregulation of genes associated with efflux pumps (mexA, mexB, oprM, mexX, and mexY) and virulence factors (pelA, algD, pslA, and exoS) in the clinical isolate treated with ½ minimum inhibitory concentration (MIC) of Fe3O4@SiPr@Quercetin in combination with ½ MIC of ciprofloxacin, compared with treatment with ciprofloxacin alone. Collectively, these findings indicate that quercetin-functionalized magnetic nanoparticles may serve as a promising adjunctive therapeutic strategy for combating ciprofloxacin-resistant P. aeruginosa infections.