Abstract
White-nose syndrome is a fungal disease responsible for the rapid decline of North American bat populations. This study addressed a novel method for inactivating Pseudogymnoascus destructans, the causative agent of WNS, using ultraviolet A (UVA) or B (UVB) radiation in combination with methoxsalen, a photosensitizer from the furanocoumarin family of compounds. Fungal spore suspensions were diluted in micromolar concentrations of methoxsalen (50–500 μM), then exposed to fixed doses of UVA radiation (500–5000 mJ/cm2), followed by plating on germination media. These plates were examined for two to four weeks for evidence of spore germination or inactivation, along with resultant growth or inhibition of P. destructans colonies. Pretreatment of fungal spores with low doses of methoxsalen resulted in a UVA dose-dependent inactivation of the P. destructans spores. All doses of methoxsalen paired with 500 mJ/cm2 of UVA led to an approximate two-log10 (~99%) reduction in spore viability, and when paired with 1000 mJ/cm2, a four-log10 or greater (>99.99%) reduction in spore viability was observed. Additionally, actively growing P. destructans colonies treated directly with methoxsalen and either UVA or UVB radiation demonstrated UV dose-dependent inhibition and termination of colony growth. This novel approach of using a photosensitizer in combination with UV radiation to control fungal growth may have broad, practical application in the future.
Highlights
An alarming expansion of emerging fungal diseases, which pose significant threats to human and animal health, food security, and ecosystem stability, has accompanied widespread anthropogenic activity [1,2,3]
All doses of methoxsalen paired with 500 mJ/cm2 of ultraviolet A (UVA) led to an approximate two-log10 (~99%) reduction in spore viability, and when paired with 1000 mJ/cm2, a four-log10 or greater (>99.99%) reduction in spore viability was observed (Fig 1A)
There was a significant difference between experimental groups, and Bonferroni post hoc comparisons indicated that spores treated with methoxsalen for 15, 30, and 60 minutes prior to UVA exposure exhibited significantly less spore germination than control spores
Summary
An alarming expansion of emerging fungal diseases, which pose significant threats to human and animal health, food security, and ecosystem stability, has accompanied widespread anthropogenic activity [1,2,3]. Management of these diseases is an evolving challenge. Studies of representative mycotic diseases such as White-nose syndrome (WNS) in bats caused by Pseudogymnoascus destructans (Pd), and chytridiomycosis in amphibians caused by Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans, have documented severe population declines [1, 4]. Inactivation of the causative fungal pathogen of white-nose syndrome with methoxsalen plus ultraviolet light decision to publish, or preparation of the manuscript
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