III.3. Tools for studying the fungal exposome
Collecting, storing, and conveying environmental or human samples for fungal assessment are critical steps. This preanalytical stage needs to be planned and performed according to the desired sample nature (bioaerosol, house dust, skin, feces), to the environment (temperature, wind, relative humidity, building material) or personal conditions (adult vs child, professional vs home exposure), and to the purpose of the study (e.g. epidemiological study vs examination of a patient’s case) (61–63).
Environmental samples may be analyzed by culture-dependent and culture-independent approaches. The former requires in vitrogrowth of fungal samples prior to identification, while the latter proceeds with spore and sub-spore fragments identification, either through microscopy analysis or molecular methods. For most environmental fungal taxa, culture cannot be achieved (64). On the other hand, for those growing in vitro, their growth rate will depend on the type of fungal culture, the nutrient media in use (57). Microscopic examination allows for quantitative assessment of samples and low taxonomical detection of taxa which is a less precise approach. Immunological detection of molds using specific enzyme-linked immunoassay (ELISA) is also possible (65). Alternatively, DNA-based approaches such as polymerase chain reaction (PCR) targeting taxonomic marker sequences, or DNA metabarcoding, allow the identification of considerably higher taxonomic biodiversity within the collected samples (64,66). However, this new technology also has some shortcomings, including primer bias which can heavily alter sequencing results (67,68), or the fact that taxonomic marker sequences are not directly related to the identification of a fungal species, therefore introducing the need for operational taxonomic units (64). The usage of DNA-based procedures for characterizing environmental fungi communities includes application of PCR amplification of ribosomal RNA genes and DNA fingerprinting methods such as Denaturing Gradient Gel Electrophoresis (DGGE), which uses a genetic fingerprinting method to examine microbial communities from environmental samples. These methods provide a broad quantification of fungi identified from the environment (69,70).
A third approach gaining momentum addresses fungal exposome using statistical modeling of airborne particles based on the study of air-mass movements categorized in spatio-temporal patterns of connectivity. This approach might alleviate the labor-intensive classical identification of airborne fungal spores, and eliminate the potential bias linked to the choice of the air sampling site (71).
Studies on human mycobiota have taken advantage of the culturomics approach, which can be combined with molecular methods such as metagenomic deep sequencing, allowing the identification of more fungal taxa in patients and healthy controls (24,72).
Overview of major mold-related hypersensitivity diseases
Fungus-human host interactions involve a combination of hypersensitivity, toxicity, and opportunistic infections (26–28,73–76)(Figure 2) . Indoor and outdoor exposure to fungi is ubiquitous (33,47) and altered by climate change (29,41,77).