Background/Objectives: Parietin (PTN), a blue-light absorbing pigment from Teloschistes spp. lichens, exhibit photosensitizing properties via Type I (superoxide anion, O₂^•−) and Type II (singlet oxygen, ¹O₂) mechanisms, inactivating bacteria in vitro after photoexcitation. We evaluate the in vitro antifungal activity of PTN against Candida tropicalis biofilms under actinic irradiation, its role in O₂^•− and ¹O₂ production, and the cellular stress response. Methods: Minimum inhibitory concentration (MIC) of PTN was determined in C. tropicalis NCPF 3111 under dark and actinic light conditions. Biofilm susceptibility was assessed at MIC/2, MIC, MICx2, MICx4, and MICx6 in the same conditions, and viability was measured by colony-forming units. Photodynamic mechanisms were examined using Tiron (O₂^•− scavenger) or sodium azide (¹O₂ quencher). O₂^•− production was measured by the nitro-blue tetrazolium (NBT) reduction and nitric oxide (NO) generation by Griess assay. Total antioxidant capacity was studied by FRAP (Ferrous Reduction Antioxidant Potency) assay and superoxide dismutase (SOD) activity by NBT assay. Results: Photoexcitation of PTN reduced C. tropicalis biofilm viability by four logs at MICx2. Sodium azide partially reversed the effect, whereas Tiron fully inhibited it, indicating the critical role of O₂^•−. PTN also increased O₂^•− and NO levels, enhancing SOD activity and FRAP. However, this antioxidant response was insufficient to prevent biofilm photoinactivation. Conclusions: Photoinactivation of C. tropicalis biofilms by PTN is primarily mediated by O₂^•−, with a minor contribution from ¹O₂ and an imbalance in NO levels. These findings suggest PTN is a promising photosensitizer for antifungal photodynamic therapy.

Background/Objectives: Parietin (PTN), a blue-light absorbing pigment from Teloschistes spp. lichens, exhibits photosensitizing properties via Type I (superoxide anion, O2•-) and Type II (singlet oxygen, 1O2) mechanism, inactivating bacteria in vitro after photo-stimulation. We evaluate the in vitro antifungal activity of PTN against Candida tropicalis biofilms under actinic irradiation, its role in O2•- and 1O2 production, and the cellular stress response. Methods: Minimum Inhibitory Concentration (MIC) of PTN was determined in C. tropicalis NCPF 3111 under dark and actinic light conditions. Biofilm susceptibility was assessed at MIC/2, MIC, MICx2, MICx4 and MICx6 in the same conditions, and viability was measured by colony forming units. Photodynamic mechanisms were examined using Tiron (O2•- quencher) or sodium azide (1O2 scavenger). O2•- production was measured by the Nitro-Blue tetrazolium (NBT) reduction and nitric oxide (NO) by Griess assay. Total antioxidant capacity was studied by FRAP (Ferrous Reduction Antioxidant Potency) assay and superoxide dismutase (SOD) activity by NBT assay. Results: Photo-stimulation of PTN reduced C. tropicalis biofilm viability by 4-logs at MICx2. Sodium azide partially reversed the effect, whereas Tiron fully inhibited it, indicating the critical role of O₂•⁻. PTN also increased O₂•⁻ and NO levels, enhancing SOD activity and FRAP. However, this antioxidant response was insufficient to prevent biofilm photoinactivation. Conclusions: Photoinactivation of C. tropicalis biofilms by PTN is primarily mediated by O2•-, with a minor contribution from ¹O₂ and an imbalance in NO levels. These findings suggest PTN as a promising photosensitizer for antifungal photodynamic therapy.

Medicinal plants have been explored worldwide as potential alternatives for the prevention and treatment of different diseases, including viral infections. Baccharis crispa Spreng. (Asteraceae) is a native medicinal species widely used in South America. Given the influence of genetic and environmental factors on secondary metabolites biosynthesis and accumulation, this study aimed to evaluate the in vitro antiviral activity of four wild populations of B. crispa from Córdoba, Argentina, and assess the variability in their bioactivity and chemical composition. The cytotoxicity of chloroform, ethanol, and aqueous extracts from aerial parts was evaluated by the neutral red uptake method. Antiviral and virucidal activity against herpes simplex virus type 1 (HSV-1) and chikungunya virus (CHIKV) were assessed via plaque-forming unit (PFU) reduction assay. Phytochemical analyses of the extracts were conducted using HPLC-ESI- MS/MS. The Puesto Pedernera population showed the strongest antiviral activity, with inhibition rates of 82% for CHIKV and 79% against HSV-1, as well as potent virucidal effects, reducing PFU formation by up to 5 logarithms for both viruses. Remarkably, ethanol extract exhibited the least toxicity and strongest inhibitory activity. Villa del Parque population was inactive. We identified 38 secondary metabolites, predominantly phenolic acids (12) and flavonoids (18), in varying proportions. Delphinidin and delphinidin-3-glucoside are described for the first time in the species. Differences in phytochemical profiles were observed among extract types and populations. Key phenolic compounds showed moderate positive correlations with the evaluated bioactivities, emphasizing the complexity of phytochemical properties and interactions. These results highlight the therapeutic potential of B. crispa extracts against viral infections and underscore the importance of considering the geographical source of plant material in bioactivity evaluations.