In vitro eradication of Fusarium oxysporium conidia using light-triggered thiopyridinium porphyrin-cyclodextrin dyes

The genus Fusarium comprises filamentous fungi widely distributed in soil and plants, representing threats to various organisms, including plants, animals, and humans. Conventional fungicides have limitations, leading to a growing interest in sustainable control methods such as photodynamic inactivation (PDI) of microorganisms. This study evaluates the antifungal photodynamic activity of meso-substituted porphyrin derivatives (H₂Pors 1a–3a), which each structure is composed by three thiopyridinium groups and one cyclodextrin group (α-, β-, or γ-CD). These water-soluble porphyrin-cyclodextrin derivatives were prepared and tested on Fusarium oxysporium conidia. Photoinactivation tests were conducted at different concentrations (1.0, 2.5, and 5.0 μM) under white light exposure at an irradiance of 25 mW.cm⁻² for 60 min (light dose of 90 J.cm⁻²). Fungal inactivation was observed for all molecules at the highest tested concentration. H₂Por 3a demonstrated the strongest PDI effect, achieving complete inactivation of the conidia (5.0 log₁₀ viability reduction) at 2.5 and 5.0 μM and partially at 1.0 μM (∼3.0 log₁₀ viability reduction). H₂Por 1a showed similar results to H₂Por 3a at the highest concentration, but was less effective at the lowest concentration. H₂Por 2a showed partial inactivation of the fungi at the highest tested concentration of 5.0 μM (2 log₁₀ viability reduction). This lower antifungal activity is attributed to the β-CD forming aggregates in water. These findings suggest that H₂Pors 1a and 3a are promising drugs for the photoinactivation of F. oxysporium conidia.