Bats Increase the Number of Cultivable Airborne Fungi in the “Nietoperek” Bat Reserve in Western Poland

The “Nietoperek” bat reserve located in Western Poland is one of the largest bat hibernation sites in the European Union with nearly 38,000 bats from 12 species. Nietoperek is part of a built underground fortification system from WWII. The aims of the study were (1) to determine the fungal species composition and changes during hibernation season in relation to bat number and microclimatic conditions and (2) evaluate the potential threat of fungi for bat assemblages and humans visiting the complex. Airborne fungi were collected in the beginning, middle and end of hibernation period (9 November 2013 and 17 January and 15 March 2014) in 12 study sites, one outside and 11 inside the complex. Ambient temperature (T ₐ) and relative humidity (RH) were measured by the use of data loggers, and species composition of bats was recorded from the study sites. The collision method (Air Ideal 3P) sampler was used to detect 34 species of airborne fungi including Pseudogymnoascus destructans (Pd). The density of airborne fungi isolated from the outdoor air samples varied from 102 to 242 CFU/1 m³ of air and from 12 to 1198 CFU in the underground air samples. There was a positive relationship between number of bats and the concentration of fungi. The concentration of airborne fungi increased with the increase of bats number. Analysis of other possible ways of spore transport to the underground indicated that the number of bats was the primary factor determining the number of fungal spores in that hibernation site. Microclimatic conditions where Pd was found (median 8.7 °C, min-max 6.1–9.9 °C and 100 %, min-max 77.5–100.0 %) were preferred by hibernating Myotis myotis and Myotis daubentonii; therefore, these species are most probably especially prone to infection by this fungi species. The spores of fungi found in the underground can be pathogenic for humans and animals, especially for immunocompromised persons, even though their concentrations did not exceed limits and norms established as dangerous for human health. In addition, we showed for the first time that the air in bats hibernation sites can be a reservoir of Pd. Therefore, further study in other underground environments and wintering bats is necessary to find out more about the potential threat of airborne fungi to bats and public health.