The potential role of bat epidermal microbes in biological control of white-nose syndrome

Background/Question/Methods

White-nose syndrome (WNS) is a fungal disease that has decimated hibernating bat populations in the eastern United States.  The possibility that the pathogen (Geomyces destructans) will appear in the western United States and incite epidemics there is a serious concern.  For a cutaneous fungal pathogen like G. destructans, initial contact with the host, and subsequent spore germination followed by penetration of the host epidermis, are points in the infection process that determine whether disease will progress.  The resident microbiota of the bat epidermis may interact with pathogens by preemptive skin colonization, nutrient competition, or production of inhibitory compounds.  Bat epidermal microbes were isolated to evaluate their potential to inhibit G. destructans.  Over a two-year period, samples were obtained from hibernating bats at locations in New York, West Virginia, Missouri, Wisconsin, and Idaho.  Samples were obtained by gently scrubbing wing skin with sterile cotton swabs moistened with saline.  Adherent bacterial and fungal cells on swabs were transferred to growth media (Tryptic Soy Agar for bacteria; Corn Meal Agar, Sabourauds dextrose agar for fungi).   Organisms were obtained in pure culture, and initial screening was done for inhibition of G. destructans in paired culture experiments.

Results/Conclusions

A large number and variety of fungi were recovered from bat wing skin, with a smaller representation of bacterial phenotypes.  Some phenotypes were common among bats from different sample locations.  Dematiaceous hyphomycetes (conidial fungi with dark brown/green/black colonies) were common (Alternaria, Cladosporium, others), as was Penicillium.  Numerous samples yielded pink yeast colonies, likely Rhodotorula (known to colonize plants, mammals, soil, and bat guano).  Pale yellow, Gram-negative bacterial colonies were common, and further identification of bacterial isolates is pending.  Several fungal isolates inhibited radial growth of G. destructans in paired culture experiments using agar plates.  Those fungi and bacteria which are identified as potential inhibitory agents will be further characterized as to environmental and nutritional growth requirements, for selection of those agents best suited for in vivo biological control trials.  Quantitative and qualitative differences in the resident epidermal microbiota of bats may provide insight into differential susceptibility (e.g., by species or location) of bats to infection by G. destructans, as well as a potential control measure for this disease.