Phloxine B-chitosan films as light-activated antibacterial coatings

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 log₁₀ reduction) and Pseudomonas aeruginosa (2 log₁₀ reduction), while also significantly reducing the bacterial load in Staphylococcus aureus biofilms (2 log₁₀ reduction). This approach presents a promising strategy for localized, antibiotic-free treatment of infected wounds.