Rutin-luteolin flavonoid-encapsulated chitosan nanoparticles: a novel strategy to combat multidrug-resistant Pseudomonas aeruginosa.

Pseudomonas aeruginosa (P. aeruginosa) is a major opportunistic pathogen with strong biofilm-forming ability and high resistance to antibiotics. Natural flavonoids such as rutin and luteolin possess antimicrobial potential, but their poor solubility and bioavailability limit therapeutic applications. This study evaluated the antibacterial and anti-biofilm efficacy of rutin–luteolin encapsulated chitosan nanoparticles (RUT-LUT-CS) against clinical and reference strains of P. aeruginosa. RUT-LUT-CS nanoparticles were spherical with an average size of 285 nm (FESEM), hydrodynamic diameter of 470 nm (DLS), and a positive zeta potential of + 31.8 mV. Antimicrobial susceptibility assays showed that RUT-LUT-CS reduced MIC and MBC values four-fold (0.78 and 1.56 mg/mL) compared to free RUT-LUT (3.125 and 6.25 mg/mL). Agar-well diffusion demonstrated inhibition zones of 22–29 mm for RUT-LUT-CS versus 15–23 mm for free compounds. Biofilm assays revealed that RUT-LUT-CS inhibited biofilm formation by > 70%, reducing activity from strong to poor categories in all isolates, while free RUT-LUT achieved only ~ 40–50% inhibition. Gene expression analysis further confirmed significant downregulation, with pelA reduced by 70–80% and rhlR by 55–65% relative to untreated controls. RUT-LUT-CS nanoparticles exhibit superior antimicrobial and anti-biofilm activities compared with free flavonoids, suggesting strong potential as an effective therapeutic strategy against multidrug-resistant P. aeruginosa.