Potential of using medicinal plant extracts as photosensitizers for antimicrobial photodynamic therapy

Abstract

Abstract Antimicrobial photodynamic therapy (APDT) is a promising approach to overcome antimicrobial resistance. However, for widespread implementation of this approach, approved photosensitizers are needed. In this study, we used commercially available preparations ( Calendulae officinalis floridis extract, Chamomillae recutitae floridis extract, Achillea millefolii herbae extract; Hypericum perforatum extract; Eucalyptus viminalis folia extract) as photosensitizers for inactivation of gram‐negative ( Pseudomonas aeruginosa ) and gram‐positive ( Staphylococcus aureus ) bacteria. Spectral‐luminescent analysis has shown that the major chromophores are of chlorophyll (mainly chlorophyll a and b ) and hypericin nature. The extracts are efficient generators of singlet oxygen with quantum yield ( γ Δ ) from 0.40 to 0.64 (reference compound, methylene blue with γ Δ = 0.52). In APDT assays, bacteria before irradiation were incubated with extracts for 30 min. After irradiation and 24 h of incubation, colony‐forming units (CFU) were counted. Upon exposure of P. aeruginosa to radiation of 405 nm, 590 nm, and 660 nm at equal energy dose of 30 J/cm 2 (irradiance – 100 mW/cm 2 , exposure time – 5 min), the most pronounced effect is observed with blue light (>3 log 10 reduction); in case of S. aureus , the effect is approximately equivalent for light of indicated wavelengths and dose ( > 4 log 10 reduction).