Mechanistic study of the photodynamic inactivation of human and plant pathogenic fungi

Abstract

The increasing emergence of fungicide tolerance among many species of human and plant-pathogenic fungi has stimulated the development of different approaches to control this group of pathogens. Antifungal photodynamic treatment (APDT) is a promising alternative to conventional fungicides that can be used to treat localized mycoses in humans as well to reduce the population of pathogenic fungi in the environment. The process involves the use of a non-toxic light activated photosensitizer which selectively accumulates into the target-cells. In the presence of oxygen, the excited state PS induces the formation of several reactive oxygen species that kill the microorganism without significant damage to the host. Although very promising, the use of APDT to treat mycosis has not been much developed and APDT has not been used to control phytopathogenic species. The objectives of the present study are: (1) to identify novel PS more effective for the treatment of localized mycosis in humans and for the photodynamic inactivation of phytopathogenic fungi; (2) to determine the mechanism of action of the novel PS in metabolically active structures such as hyphae and yeast cells as well as in quiescent structures such as conidia, in species of the genera Candida, Trychophyton, Colletotrichum and Aspergillus; (3) to evaluate and characterize the damage of the photodynamic treatment with the novel PS on cells and tissues of the fungal hosts and (4) to isolate (from Citrus species), identify, and evaluate the potential of coumarinic and furanocoumarinic PS for APDT of phytopathogenic fungi. The expected contributions include: (1) the improvement of the efficacy of APDT for the treatment of human mycosis, the supply of the necessary foundation for the use of APDT to control phytopathogenic fungi and the improvement of the mechanistic understanding of APDT with the novel PS on the specialized structures of the different fungal species. (AU)