Novel inactivation of the causative fungal pathogen of white-nose syndrome with methoxsalen plus ultraviolet A or B radiation

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/cm 2), 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/cm 2 of UVA led to an approximate two-log 10 (~99%) reduction in spore viability, and when paired with 1000 mJ/cm 2 , a four-log 10 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.

Whole‐room ultraviolet sanitization as a method for the site‐level treatment of Pseudogymnoascus destructans

“…Therefore, late summer UV treatments of environmental reservoirs are predicted to reduce P. destructans loads throughout the hibernation season (and therefore, infection severity) and do not jeopardize the safety of hibernating bats. Recently, UV‐A or UV‐B light in combination with the photosensitizer methoxsalen has been shown capable of eliminating P. destructans in a laboratory setting (Hartman et al, 2020). UV‐A and UV‐B lights are far less harmful to organisms than UV‐C, possibly further decreasing potential environmental impacts.…”

“…UV-A and UV-B lights are far less harmful to organisms than UV-C, possibly further decreasing potential environmental impacts. Methoxsalen is not thought to have significant negative environmental impacts on subterranean biota, although tests of its' impact on cave microbes have not been performed (Hartman et al, 2020). Whole-room sanitizing units, such as the one used in this study, could be equipped with UV-A/B emitting bulbs instead of UV-C bulbs providing an efficient means of distributing this treatment form, following environmental dispersion of methoxsalen.…”

Development of a multi-year white-nose syndrome mitigation strategy using antifungal volatile organic compounds

“…A number of potential mitigation methods have been developed or experimentally tested against P. destructans or treating white-nose syndrome, including chemical agents [14][15][16][17][18][19][20], microbial antagonists [21][22][23][24][25][26][27], environmental modulation [28,29], UV light exposure [30][31][32], antibiotics [33], vaccination [34], and electrolyte supplementation [35], among others. Of these, the greatest interest has been in the use of chemical and microbial agents to inhibit the growth and pathogenicity of P. destructans.…”