From Bacterial Extract to Breakthrough Therapy: Pseudomonas fluorescens-Enabled Green Synthesis of pH-Responsive Chitosan–Silver Hybrid Nanoparticles for Next-Generation Pulmonary Drug Delivery Anti-MDR Treatment

Background: Multidrug-resistant (MDR) pulmonary infections represent a critical global health challenge, necessitating innovative therapeutic approaches. Green synthesis methodologies offer sustainable alternatives for nanoparticle fabrication while addressing antimicrobial resistance. Methods: Stimuli-responsive chitosan–silver hybrid nanoparticles (CS–Ag HNPs) were biosynthesized using Pseudomonas fluorescens bacterial extracts and loaded with ciprofloxacin for targeted pulmonary delivery. Comprehensive characterization included dynamic light scattering, transmission electron microscopy, UV–visible spectroscopy, and aerodynamic assessment via next-generation impactor. Antimicrobial efficacy was evaluated against MDR Pseudomonas aeruginosa and Klebsiella pneumoniae, including biofilm disruption studies, and biocompatibility was assessed. Molecular docking analysis elucidated binding mechanisms. Cytotoxicity and epithelial barrier integrity were evaluated using Calu-3 cell models. Results: The biosynthesized NPs exhibited optimal physicochemical properties (180 ± 20 nm, PDI 0.21 ± 0.04, ζ-potential + 32.4 ± 3.1 mV) with high encapsulation efficiency (68.2 ± 4.0%). Aerodynamic analysis revealed excellent inhalation characteristics (MMAD 2.6 μm, FPF 65 ± 5%). The hybrid system demonstrated 4-fold enhanced antimicrobial activity against MDR pathogens and significant biofilm disruption (70% for P. aeruginosa, 65% for K. pneumoniae) compared to free ciprofloxacin. Cell viability remained ≥85% at therapeutic concentrations. Molecular docking revealed enhanced drug-target binding affinity (−11.2 vs. −9.3 kcal/mol) and multi-residue interactions. Conclusions: Green-synthesized CS–Ag HNPs represent a promising sustainable platform for combating pulmonary MDR infections through enhanced antimicrobial efficacy and optimal aerodynamic properties.