Antimicrobial photodynamic inactivation of Pseudomonas aeruginosa biofilms: a synergistic approach with berberine, gentamicin, and colistin
DOI:
https://doi.org/10.48797/sl.2025.336Keywords:
PosterAbstract
Background: Chronic wound infections caused by Pseudomonas aeruginosa biofilms are highly resistant to conventional treatments, necessitating innovative therapeutic strategies [1]. Antimicrobial photodynamic inactivation (aPDI) has proven to be a promising alternative [2]. However, its efficacy against Gram-negative bacteria remains suboptimal due to the restricted penetration of light and photosensitizers through the biofilm matrix, which hinders its full antimicrobial potential [3]. Objective: This study explores the potential of colistin (Col) at subinhibitory concentrations to enhance the photodynamic activity of a berberine-gentamicin (Ber-Gen) combination against P. aeruginosa biofilms. Methods: P. aeruginosa ATCC 10145 strain from the American Type Culture Collection was used. Col-induced membrane permeability changes were assessed by flow cytometry, and synergistic interactions within the Ber-Gen-Col combination were determined by checkerboard assay. Biofilms were exposed to blue light (420 nm, 30 mW/cm2, 10 min) after one or three aPDI cycles (administered at 24 h intervals). Treatment efficacy was evaluated by quantifying biomass (crystal violet), metabolic activity (resazurin), and culturability (CFU/cm2). The mechanism of action was examined by ROS production (fluorometry), membrane damage (microscopy), and biofilm structural changes (optical coherence tomography). Results: Colistin (4 µg/mL) increased membrane permeability by 30 %, significantly enhancing the photodynamic action of Ber-Gen-Col. The triple combination led to a nearly complete eradication of biofilm cells, achieving a 7-log CFU/cm2 reduction and over 90 % decreases in biomass and metabolic activity. However, sustained suppression of biofilm regrowth was observed only after multiple irradiation cycles, while single-cycle treatments allowed biofilm recovery within 24 h. Regarding the mechanism of action of photoactivated Ber-Gen-Col, a significant disruption of the biofilm structure, increased reactive oxygen species (ROS) generation, and extensive membrane damage were observed. Conclusion: These findings demonstrate that integrating subinhibitory Col concentrations with repeated aPDI cycles represents a promising strategy for effectively eliminating P. aeruginosa biofilms in chronic wound infections.
References
1. Serra, R. et al. Chronic wound infections: the role of Pseudomonas aeruginosa and Staphylococcus aureus. Expert review of anti-infective therapy 2015, 13(5), 605-613 doi: 10.1586/14787210.2015.1023291
2. Gonçalves, A.S.C. et al. New Insights on Antibacterial Mode of Action of Blue-Light Photoactivated Berberine and Curcumin-Antibiotic Combinations Against Staphylococcus aureus. Photodiagnosis and Photodynamic Therapy 2025, 52, 104514, doi: 10.1016/j.pdpdt.2025.104514
3. Branco, T.M. et al. Single and combined effects of photodynamic therapy and antibiotics to inactivate Staphylococcus aureus on skin, Photodiagnosis and Photodynamic Therapy 2018, 21, 285-293, doi: 10.1016/j.pdpdt.2018.01.001
Downloads
Published
How to Cite
Issue
Section
License
Copyright (c) 2025 Ariana S. C. Gonçalves, Manuel Simões, Anabela Borges

This work is licensed under a Creative Commons Attribution 4.0 International License.
In Scientific Letters, articles are published under a CC-BY license (Creative Commons Attribution 4.0 International License), the most open license available. The users can share (copy and redistribute the material in any medium or format) and adapt (remix, transform, and build upon the material for any purpose, even commercially), as long as they give appropriate credit, provide a link to the license, and indicate if changes were made (read the full text of the license terms and conditions of use).
The author is the owner of the copyright.