DETECTING VIABLE PSEUDOGYMNOASCUS DESTRUCTANS (ASCOMYCOTA: PSEUDEUROTIACEAE) FROM WALLS OF BAT HIBERNACULA: EFFECT OF CULTURE MEDIA

Abstract: Pseudogymnoascus destructans (Pd) causes the fungal disease white-nose syndrome (WNS), which has led to high mortality in some hibernating bat species in eastern North America. The ability to detect viable Pd in hibernacula is important for understanding the role the environment plays as a reservoir for infectious Pd. Previous studies have generally used the high-sugar medium Sabouraud-dextrose (SAB) and have had low yields of viable Pd from environmental samples of Pd-positive hibernacula. While cultureindependent methods (i.e., molecular genetics) have previously shown much better success in detecting Pd, these methods cannot determine viability. In 2012 and 2015, we swabbed walls in four hibernacula with WNS-positive bats in New Brunswick, Canada, and cultured the samples using dextrose-peptone-yeast extract agar (DPYA), SAB, and Malt extract (MEA) media. Samples cultured on DPYA produced viable Pd 43.7 to 50.0 % more frequently than SAB, with a maximum overall return for DPYA among sites of 62.5 % Pd-positive samples over both years. During the initial outbreak of WNS in our study region, Pd-positive swabs were produced from 40.0 to 83.3 % of samples on DPYA, whereas SAB produced a maximum of 40.0 %. At one site we detected Pd from 83.3% of swabs cultured on DPYA and 0 % on SAB. MEA produced no viable Pd. Our figures for Pd detection are as high as or higher than previously published culture-independent methods, while also confirming the viability of the Pd present. We found that the yield of viable Pd from hibernacula walls decreased from 2012 to 2015 as the hibernating bat population decreased due to WNS mortality, but patterns varied amongst hibernacula, and overall, were not statistically different. It is possible that environmental growth of Pd contributes to its persistence within hibernacula. We suggest that future studies on the environmental persistence of viable Pd discontinue the use of high-sugar media that lack inhibitory fungal growth ingredients, such as SAB and MEA, as they favor fast-growing fungal species that overgrow and mask slowergrowing fungi such as Pd