Repurposing bacterial lysates: Engineering inhalable locust bean gum microparticles for respiratory infection prevention

This study explores the development of inhalable microparticles containing bacterial lysates (BL) from multiple relevant bacterial species that include Staphylococcus aureus, Streptococcus pyogenes and Klebsiella pneumoniae, and locust bean gum (LBG) for pulmonary immunization against respiratory infections. LBG, a galactomannan, was chosen for its mucoadhesive properties and affinity for antigen-presenting cells. Microparticles were prepared by spray-drying, testing different LBG:BL ratios. The morphological analysis revealed convoluted microparticles, and BL association efficiency up to 81 % was determined. Antigenic assays confirmed that bacterial antigens of S. pyogenes, used as reference, remained preserved on the microparticles despite the applied processing conditions. The aerodynamic analysis showed that lower BL content (LBG:BL = 10:0.2, w/w) produced more suitable particles for pulmonary delivery, with 4.6 μm mass median aerodynamic diameter (MMAD) and 29 % fine particle fraction (FPF). Fluorescence microscopy confirmed uniform distribution of BL within the LBG matrix and LBG microparticles demonstrated superior adhesive properties compared to controls. Sustained release of BL from microparticles was observed in vitro, reaching around 80 % after 6 h, which increased to around 85 % after 24 h. Cytotoxicity studies showed appropriate cell viability at physiologically relevant concentrations (around 70 % or more). These findings suggest that LBG-based microparticles loaded with BL have potential to be explored as inhalable formulation for prevention of respiratory infections, offering targeted delivery and prolonged antigen presentation to enhance immune responses.