Determination and assessment of airborne fungal particles is complex and results of different sampling and analytical strategies are hard to compare due to limitations of each of the techniques. Here, an indoor mold detection system based on quantitative polymerase chain reaction (qPCR) is described and validated for its reliability and stability to identify airborne fungal particles collected. Data obtained from testing the system with fungal DNA, spore suspensions and bioaerosols indicated a need for spiking and normalization of measurements due to material loss and assay specific bias. Considering the loss of material during sample processing, detection limits defined for suspensions of Tritirachium oryzae spores were roughly 18 spores per sample. Detection of fungal spore mixtures nebulized under controlled conditions in a bioaerosol chamber showed generally 2-3 times higher normalized values measured with the molecular system compared to cultivation. Data obtained from a mold infested indoor sampling site and its corresponding outdoor reference measurement showed good correlations between qPCR and high-throughput sequencing (rho = 0.83, p < 0.01), if Cladosporium species were excluded. Taking necessary data normalization into account, the described qPCR detection system shows great potential to complement commonly used culture based approaches with the aim to improve the precision of indoor mold assessments. In contrast to already available qPCR assays that detect certain molds on a species level, this system covers a broad range of relevant fungal communities, serving as a promising alternative to high-throughput sequencing to identify indoor molds.
Although numerous bioaerosol samplers for counting and identifying airborne microorganisms are available, the considerably high purchase and maintenance costs for the sampler often prevent broad monitoring campaigns for occupational or environmental surveillance of bioaerosols. We present here a newly developed simple adapter and filter system (TOP filter system) designed to collect bioaerosol particles from a defined air volume using conventional vacuum cleaners as air pumps. We characterized the physical properties of the system using air flow measurements and validated the biological performance. The culture-based detection capacities for airborne fungal species were compared to a standard impaction sampler (MAS-100 NT) under controlled conditions in a bioaerosol chamber (using Trichoderma spores as the test organism) as well as in the field. In the chamber, an overall equivalent detection capacity between all tested filters was recorded, although a significant underrepresentation of the TOP filter system for Trichoderma spores were seen in comparison to the MAS-100 NT. In a comparative field study (n = 345), the system showed similar biological sampling efficiencies compared to the MAS-100 NT impactor, only the diversity of identified fungal communities was slightly lower on the filters. Thus, the system is suitable for large-scale environmental sampling operations where many samples have to be taken in parallel at a given time at distant locations. This system would allow endeavors such as antibiotics resistance monitoring or hygiene surveys in agricultural or occupational settings.
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