Assessment of bacterial contamination of air at the Museum of King John's III Palace at Wilanow (Warsaw, Poland) – selection of an optimal growth medium for analysis of the diversity of airborne bacteria

Currently, there is no standardized protocol for the assessment of microbial air contamination in museums and other cultural heritage objects open for visitors. Therefore, most museums conduct this type of assessments based on their own guidelines or good practices. Usually, microbial air contamination is assessed using only methods of classical microbiology with application of a single growth medium. Therefore, this medium should be carefully selected to limit the bias of selective cultivation. In this study we used metabarcoding, i.e. NGS-based method, combined with the classical microbiological culturing to assess the effectiveness of various media application in microbiological screening at the Museum of King John's III Palace at Wilanow (Warsaw, Poland). Our results indicated that when using classical microbiology approach to the assessment of microbial air contamination in museums selecting of a proper growth medium is critical. It was shown that the use of rich media (commonly applied by museums' conservators) introduce significant bias by severely underreporting bacterial species most probably involved in biodeterioration and putative human pathogens. Therefore, we postulate the use of other media, such as Frazier or R2A medium, as they can yield more diverse communities. Moreover, in this study, we introduced a possibility of combining novel NGS methods with classical microbiology for an improved assessment of microbial air contamination in museums.