Targeting planktonic uropathogens and Escherichia coli biofilm with photodynamic therapy mediated by methylene blue and potassium iodide.

Authors

Daniela Silva, Inês Mendonça, Cátia Vieira, M Graça P M S Neves, M Amparo Faustino, Maria Bartolomeu, Adelaide Almeida

Published in

Journal of photochemistry and photobiology. B, Biology. Volume 283. Pages 113551. Aug 27, 2026. Epub Aug 27, 2026.

Abstract

Urinary tract infections (UTIs) are among the most common infections worldwide, with many hospital-acquired cases linked to biofilm formation on urinary catheter surfaces. The growing problem of antimicrobial resistance limits the effectiveness of conventional antibiotics, and antimicrobial photodynamic therapy (aPDT) has emerged as a promising alternative. This approach is based on the combination of a photosensitizer (PS), dioxygen, and visible light to reduce bacterial concentration without promoting resistance. In this study, the potential of aPDT in controlling UTIs was evaluated using a well-studied PS, methylene blue (MB), alone or in the presence of potassium iodide (KI). Ex vivo assays in urine were conducted using the five most common UTI-causing bacteria: Klebsiella pneumoniae, Escherichia coli, Enterococcus faecalis, Proteus mirabilis, and Pseudomonas aeruginosa. MB alone effectively photoinactivated E. coli, P. mirabilis, and E. faecalis in planktonic form, with limited activity against K. pneumoniae and P. aeruginosa. The addition of KI significantly enhanced the photodynamic effect against all tested strains, resulting in a reduced treatment time, and was also effective against mixed bacterial populations in the planktonic state. The efficacy of the treatments was further evaluated against E. coli cells within biofilms formed on urinary catheter surfaces. The combined action of MB and KI successfully controlled E. coli biofilms, achieving reductions of 3.9 (> 99.987%) and 6.0 log₁₀ CFU mL^-1 after one and two aPDT treatment cycles, respectively. Overall, these findings highlight MB + KI-mediated aPDT as a promising strategy for the photoinactivation of planktonic uropathogens and E. coli biofilms formed on urinary catheter surfaces.

PMID:
42667816
Bibliographic data and abstract were imported from PubMed on 30 Aug 2026.

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