Clavibacter michiganensis causes significant crop losses in tomatoes, and the disease may be transferred by plant seeds. This study evaluates the efficacy of Photodynamic Inactivation (PDI) with a water-soluble hypericin derivative, developed as a complex with polyvinylpyrrolidone (high hypericin-loaded PVP, HHL-PVP), as a decontamination strategy for tomato seeds. HHL-PVP was chosen for its overall stability, as the complex remains stable in solution for over 950 days, maintains its absorption capacity after illumination with 200 J·cm⁻², and produces reactive oxygen species (ROS) even at concentrations as low as 1 µM. PDI against C. michiganensis with 5 μM HHL-PVP, 10 min drug to light interval (DLI), and illumination with red light (600–700 nm, 100 J·cm⁻²) exceeded the antimicrobial effect of a 99.9% reduction in liquid culture. Increasing the DLI to 24 h did not alter the photokilling effect. A 14 h light/10 h dark cycle in white light (118 J·cm⁻²) with 0.3 µM HHL-PVP inhibited the growth of C. michiganensis by more than 6 log₁₀ steps, indicating that HHL-PVP has a stable and long-lasting photokilling effect. The combination of HHL-PVP with potassium iodide (KI, 100 mM) completely eradicated C. michiganensis in liquid culture with red and white light, indicating KI’s role in enhancing phototoxicity. Tomato seed photodynamic decontamination using 1.0 µM HHL-PVP activated by 200 J·cm⁻² white light inactivated >5 log₁₀ of C. michiganensis, without diminishing sprouting. An addition of 100 mM KI increased the percentage of sprouted seedlings and inactivated 100% of bacteria. These results demonstrate that HHL-PVP-mediated PDI combined with KI could be highly effective as a preventative strategy in tomato protection against C. michiganensis.

Background: High hypericin-loaded polyvinylpyrrolidone (HHL-PVP) constitutes a novel approach to utilize the promising characteristics of hypericin for photodynamic diagnosis (PDD) and therapy (PDT) of brain tumors in an orally bioavailable formulation. The aim of this study was to investigate the ability of a Complementary Metal-Oxide-Semiconductor (CMOS) camera-based fluorescence imaging system to selectively visualize HHL-PVP in glioblastoma tissue even in the presence of 5-Aminolvevulinic acid (5-ALA) induced fluorescence, which is widely utilized in brain tumor surgery. Methods: We applied a previously established system with a non-hypericin specific filter for 5-ALA fluorescence visualization and a newly introduced hypericin-specific filter at 575–615 nm that transmits the spectrum of hypericin, but not 5-ALA fluorescence. Glioblastoma specimens obtained from 12 patients (11 with preoperative 5-ALA intake) were ex vivo incubated with HHL-PVP. Subsequently, fluorescence intensity and lifetime changes using both the non-hypericin specific filter and hypericin-specific filter were measured before and after HHL-PVP incubation and after subsequent rinsing. Results: While no significant differences in fluorescence signal were observed using the non-hypericin specific filter, statistically significant increases in fluorescence intensity (p = 0.001) and lifetime (p = 0.028) after HHL-PVP incubation were demonstrated using the hypericin-specific filter. In consequence, specimens treated with HHL-PVP could be identified according to the fluorescence signal with high diagnostic sensitivity (87.5%) and specificity (100%). Conclusions: Our CMOS camera-based system with a hypericin-specific filter is capable of selectively visualizing hypericin fluorescence in glioblastoma tissue after ex vivo HHL-PVP incubation. In the future, this technique could facilitate clinical investigations of HHL-PVP for PDD and PDT while maintaining the current standard of care with 5-ALA guidance.

Background/Objectives: Curcumin is a food-grade (E100) photosensitiser with promising antimicrobial properties, but its applicability is limited due to low water-solubility. Complexation of curcumin with hydroxypropyl-γ-cyclodextrin (HP-γ-CD) overcomes this constraint and may facilitate using a single photosensitiser for Photodynamic Inactivation (PDI) of pathogens along the food-production chain and within a One Health framework. Methods: In this study, a novel method to complex HP-γ-CD and curcumin (abbreviated as CD-Cur) was developed and the compound was tested against Escherichia coli, Salmonella enterica, and Candidozyma auris, in liquid culture and in situ on abiotic surfaces, food matrices, and a porcine skin model. Results: Planktonic experiments demonstrated concentration-dependent PDI efficacy with photokilling exceeding the 3 log₁₀ threshold for all tested organisms at CD-Cur concentrations between 10 and 50 µM, illuminated with 435 nm (50 J/cm²) LED light, while dark and light toxicity remained below microbiologically relevant levels. CD-Cur induced high reductions of viable E. coli on food-contact plastic foil (3.35 log₁₀, 100 µM, white light, 100 J/cm²) and on abiotic surfaces (5.17–5.50 log₁₀, 30 µM, 435 nm, 25 J/cm²) with visible photobleaching of the photosensitiser after illumination. On salmon and pistachios, matrix-dependent effects were observed, but PDI still achieved practically relevant reductions (2.25–3.52 log₁₀, 30 µM, 435 nm, 200 J/cm²) of S. enterica without visible colour alteration of the food. In a porcine skin model, CD-Cur in a 1% hydroxyethyl cellulose hydrogel reduced C. auris contamination notably. The addition of 2 mM EDTA further enhanced antifungal effects, indicating that CD-Cur can also be applied in a medical context as topical application on porcine skin (2.41 log₁₀, 500 µM, 435 nm, 75 J/cm²). Conclusions: Together, these results show that a single, photodynamic system based on food-grade CD-Cur can provide broad antimicrobial efficacy across diverse matrices and pathogens in a One Health context.