Phloxine B-chitosan films as light-activated antibacterial coatings

Green light-activation of the PhB-CS film in contact with S. aureus or P. aeruginosa kills the bacteria, while the film can be recovered and reused. • Photodynamic chitosan film for antibacterial wound dressings. • Phloxine B can be covalently coupled to chitosan thin films. • Phloxine B-chitosan films generate singlet oxygen upon irradiation with green light. • Films locally eradicate Staphylococcus aureus and Pseudomonas aeruginosa. • Repeated irradiation of films shows no loss of efficacy. • Irradiation of films reduces Staphylococcus aureus in biofilms by 99% Open wounds are prone to bacterial colonization and infection, often necessitating antimicrobial intervention. The escalating threat of antimicrobial resistance highlights the urgent need for development of alternative therapeutic strategies. Antimicrobial photodynamic therapy (aPDT), has demonstrated broad-spectrum efficacy, including activity against multidrug-resistant bacteria. However, topical application of free photosensitizers in wound treatment is limited by their diffusion away from the site of infection prior to light activation. To overcome this limitation, this work reports the covalent immobilization of the photosensitizer Phloxine B (PhB), an FDA-approved food coloring, onto a chitosan (CS) hydrogel via EDC/NHS chemistry to create a stable, reusable, contact-killing aPDT material. Irradiation of the PhB-CS platform reduced the bacterial burden of the two most prevalent wound pathogens, Staphylococcus aureus (5 log 10 reduction) and Pseudomonas aeruginosa (2 log 10 reduction), while also significantly reducing the bacterial load in Staphylococcus aureus biofilms (2 log 10 reduction). This approach presents a promising strategy for localized, antibiotic-free treatment of infected wounds.