Differences in VOC-metabolite profiles of Pseudogymnoascus destructans and related fungi by electronic-nose/GC analyses of headspace volatiles derived from axenic cultures
The most important disease affecting hibernating bats in North America is White-nose syndrome (WNS), caused by the psychrophilic fungal dermatophyte Pseudogymnoascus destructans. The identification of dermatophytic fungi, present on the skins of cave-dwelling bat species, is necessary to distinguish between pathogenic (disease-causing) microbes from those that are innocuous. This distinction is an important step for the early detection and identification of microbial pathogens on bat skin prior to the initiation of disease and symptom development, for the discrimination between specific microbial species interacting on the skins of hibernating bats, and for early indications of potential WNS-disease development based on inoculum potential. Early detection of P. destructans infections of WNS-susceptible bats, prior to symptom development, is essential to provide effective early treatments of WNS-diseased bats which could significantly improve their chances of survival and recovery. Current diagnostic methods using quantitative polymerase chain reaction (qPCR) for the targeted detection of specific fungal pathogens on bats require semi-invasive methods (skin swabs) that tend to arouse hibernating bats resulting in consumption of valuable fat reserves that reduce their chances of winter survival. Also, qPCR only indicates the presence and quantity (fungal loads) of specific fungal inoculum on bat skin, but does not conclusively indicate that the fungus has infected the host, or that a disease state exists, since template fungal DNA used for PCR comes from outside of the host rather than from within the host. Consequently, we are developing non-invasive methods for the early detection of WNS-disease based on the production of unique mixtures of volatile organic metabolites detected in sampled air (in proximity to bats) using a dual-technology, electronic-nose/gas chromatography device. This approach initially was tested in the current study to evaluate the potential of e-nose tools for identifying and discriminating between complex mixtures of volatile fungal metabolites produced by five Pseudogymnoascus species in pure cultures. We determined that the Heracles II enose system was effective in discriminating between P. destructans and related Pseudogymnoascus species using principal component analysis (PCA) of smellprints signatures coupled with discrimination index (DI) and GCpatterns of major VOC-peaks produced from analysis of aroma profiles of volatile metabolites in culture headspace.