Bioactive chitosan dressings functionalized with indole alkaloids suppress biofilm development and virulence traits in bacterial species relevant to wound infections.

Abstract

Aims: Chronic wound infections are frequently associated with biofilm-forming pathogens that impair healing and reduce the effectiveness of antimicrobial therapies. This study evaluated the antimicrobial, antibiofilm, synergistic, and antivirulence activities of two indole alkaloids, 3-(1H-indol-3-yl)propanoic acid (C1) and 1H-indole-2-carboxylic acid (C2), and investigated their incorporation into chitosan-based biodressings for infected wound management.

Methods and results: Antimicrobial activity was evaluated by agar diffusion, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), biofilm inhibition, and checkerboard assays. Cytotoxicity was assessed using RAW 264.7 macrophages and HaCaT keratinocytes. Biodressings were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, porosity, and release kinetics, while antimicrobial activity and gene expression were evaluated by agar diffusion and reverse transcription quantitative PCR. Both compounds exhibited broad-spectrum antibacterial activity, particularly against Staphylococcus aureus and Staphylococcus epidermidis, inhibited biofilm formation at sub-MIC concentrations, and showed synergistic or additive interactions with conventional antibiotics. The alkaloids displayed low cytotoxicity and were successfully incorporated into chitosan matrices, showing a biphasic release profile over the evaluated period while preserving antimicrobial activity. Functionalized biodressings significantly downregulated genes involved in adhesion (fimH), biofilm formation (icaA, icaD, aap, and pslA), quorum sensing (lasR), and virulence regulation (sarA).

Conclusions: Indole alkaloid-loaded chitosan biodressings constitute a promising multifunctional platform that combines antibacterial, antibiofilm, antibiotic-potentiating, and antivirulence activities while maintaining favorable cytocompatibility. These findings support further investigation of indole alkaloid-loaded chitosan biodressings as a potential biomaterial-based strategy for managing wound-associated bacterial infections.