Indirect Immunodetection of Fungal Fragments by Field Emission Scanning Electron Microscopy

Outdoor airborne allergens: Characterization, behavior and monitoring in Europe

Aeroallergens or inhalant allergens, are proteins dispersed through the air and have the potential to induce allergic conditions such as rhinitis, conjunctivitis, and asthma. Outdoor aeroallergens are found predominantly in pollen grains and fungal spores, which are allergen carriers. Aeroallergens from pollen and fungi have seasonal emission patterns that correlate with plant pollination and fungal sporulation and are strongly associated with atmospheric weather conditions. They are released when allergen carriers come in contact with the respiratory system, e.g. the nasal mucosa. In addition, due to the rupture of allergen carriers, airborne allergen molecules may be released directly into the air in the form of micronic and submicronic particles (cytoplasmic debris, cell wall fragments, droplets etc.) or adhered onto other airborne particulate matter. Therefore, aeroallergen detection strategies must consider, in addition to the allergen carriers, the allergen molecules themselves. This review article aims to present the current knowledge on inhalant allergens in the outdoor environment, their structure, localization, and factors affecting their production, transformation, release or degradation. In addition, methods for collecting and quantifying aeroallergens are listed and thoroughly discussed. Finally, the knowledge gaps, challenges and implications associated with aeroallergen analysis are described.

Divergent TLR2 and TLR4 Activation by Fungal Spores and Species Diversity in Dust from Waste Sorting Plants

This manuscript presents the results of an exploratory study on the relationships between NF-κB response through Toll-like receptor (TLR) activation by dust characterized by fungal spore concentrations and species diversity. Personal total dust samples were collected from Norwegian waste sorting plants and then characterized for fungal spores and fungal species diversity, as well as for other bioaerosol components, including endotoxins and actinobacteria. The ability of the dust to induce an NF-κB response by activating TLR2 and TLR4 in vitro was evaluated, as well as the relationship between such responses and quantifiable bioaerosol components. The average concentrations of bioaerosols were 7.23 mg total dust m^-3, 4.49 × 10⁵ fungal spores m^-3, 814 endotoxin units m^-3, and 0.6 × 10⁵ actinobacteria m^-3. The mean diversity measurements were 326, 0.59, and 3.39 for fungal richness, evenness, and Shannon index, respectively. Overall, fungal operational taxonomic units (OTUs) belonging to the Ascomycota phylum were most abundant (55%), followed by Basidiomycota (33%) and Mucoromycota (3%). All samples induced significant NF-κB responses through TLR2 and TLR4 activation. While fungal spore levels were positively associated with TLR2 and TLR4 activation, there was a trend that fungal species richness was negatively associated with the activation of these receptors. This observation supports the existence of divergent immunological response relationships between TLR activation and fungal spore levels on one hand and between TLR activation and fungal species diversity on the other. Such relationships seem to be described for the first time for dust from waste facilities. IMPORTANCE This manuscript presents results on multifactorial characterization of bioaerosol exposure in Norwegian waste sorting plants and the potential of such airborne dust to induce NF-κB reactions through TLR2 and TLR4 activations in an in vitro reporter cell model system. Our data revealed that increasing fungal spore levels in the dust is associated with increased activation of TLR2 and TLR4, whereas increasing fungal OTU richness is associated with decreasing activation of these receptors. The NF-κB-induced responses by the collected dust represent, therefore, effective measures of potential key immunological effects induced by a complex mixture of hazardous components, including characterized factors such as endotoxins, fungal spores, bacteria, and many other uncharacterized components. The key immunological events reported here are suggested as holistic alternatives to today's bioaerosol exposure characterization approaches for epidemiological studies in the future.

An assessment of occupational exposure to bioaerosols in automated versus manual waste sorting plants

Occupational exposure during waste sorting is associated with several health outcomes. This study obtained knowledge about the impact of work in fully automated waste sorting plants (AWSP; n = 3) vs manual waste sorting plants (MWSP; n = 3) on personal exposure (n = 71) to bioaerosols and exposure-related health effects. Personal full-shift air samples were collected using various filter-based active sampling devices that were placed in the workers' breathing zone. Personal exposure to inhalable and thoracic dust, endotoxin and microorganisms varied considerably between and within types of waste sorting plants (WSP). Workers at AWSP were on average exposed to 0.34 mg/m³ inhalable dust, 0.15 mg/m³ thoracic dust, and 51 EU/m³ endotoxins (geometric mean (GM) levels), whereas GM exposure levels at MWSP were 0.66 mg/m³ for inhalable dust, 0.44 mg/m³ for thoracic dust, and 32 EU/m³ for endotoxins. Exposure to submicronic fungal fragments did not differ between types of plants and ranged from levels below the detection limit (limit of detection, LOD) to levels in the order of 10⁶ fragments/m³. Higher levels of fungal fragments and fungal spores were found at AWSP compared to MWSP with a GM of 2.1 × 10⁵ spores/m³and with a GM of 1.2 × 10⁵ spores/m³, respectively. Actinobacterial spores were found in samples from AWSP only, with exposure levels ranging from 1.9 × 10⁴ to 1.1 × 10⁷ spores/m³. Exposure to microbial DNA varied within and between WSP and was on average in the order of 10⁴ copies/m³ for fungi and 10⁵ copies/m³ for bacteria. Health symptoms, such as sneezing, congested nose and runny nose were significantly more common among exposed workers compared to the unexposed control group.

Categorisation of culturable bioaerosols in a fruit juice manufacturing facility

Bioaerosols are defined as aerosols that comprise particles of biological origin or activity that may affect living organisms through infectivity, allergenicity, toxicity, or through pharmacological or other processes. Interest in bioaerosol exposure has increased over the last few decades. Exposure to bioaerosols may cause three major problems in the food industry, namely: (i) contamination of food (spoilage); (ii) allergic reactions in individual consumers; or (iii) infection by means of pathogenic microorganisms present in the aerosol. The aim of this study was to characterise the culturable fraction of bioaerosols in the production environment of a fruit juice manufacturing facility and categorise isolates as harmful, innocuous or potentially beneficial to the industry, personnel and environment. Active sampling was used to collect representative samples of five areas in the facility during peak and off-peak seasons. Areas included the entrance, preparation and mixing area, between production lines, bottle dispersion and filling stations. Microbes were isolated and identified using 16S, 26S or ITS amplicon sequencing. High microbial counts and species diversity were detected in the facility. 239 bacteria, 41 yeasts and 43 moulds were isolated from the air in the production environment. Isolates were categorised into three main groups, namely 27 innocuous, 26 useful and 39 harmful bioaerosols. Harmful bioaerosols belonging to the genera Staphylococcus, Pseudomonas, Penicillium and Candida were present. Although innocuous and useful bioaerosols do not negatively influence human health their presence act as an indicator that an ideal environment exists for possible harmful bioaerosols to emerge.

Characterization and pro-inflammatory potential of indoor mold particles

A number of epidemiological studies find an association between indoor air dampness and respiratory health effects. This is often suggested to be linked to enhanced mold growth. However, the role of mold is obviously difficult to disentangle from other dampness-related exposure including microbes as well as non-biological particles and chemical pollutants. The association may partly be due to visible mycelial growth and a characteristic musty smell of mold. Thus, the potential role of mold exposure should be further explored by evaluating information from experimental studies elucidating possible mechanistic links. Such studies show that exposure to spores and hyphal fragments may act as allergens and pro-inflammatory mediators and that they may damage airways by the production of toxins, enzymes, and volatile organic compounds. In the present review, we hypothesize that continuous exposure to mold particles may result in chronic low-grade pro-inflammatory responses contributing to respiratory diseases. We summarize some of the main methods for detection and characterization of fungal aerosols and highlight in vitro research elucidating how molds may induce toxicity and pro-inflammatory reactions in human cell models relevant for airway exposure. Data suggest that the fraction of fungal hyphal fragments in indoor air is much higher than that of airborne spores, and the hyphal fragments often have a higher pro-inflammatory potential. Thus, hyphal fragments of prevalent mold species with strong pro-inflammatory potential may be particularly relevant candidates for respiratory diseases associated with damp/mold-contaminated indoor air. Future studies linking of indoor air dampness with health effects should assess the toxicity and pro-inflammatory potential of indoor air particulate matter and combined this information with a better characterization of biological components including hyphal fragments from both pathogenic and non-pathogenic mold species. Such studies may increase our understanding of the potential role of mold exposure.

Cultivation and aerosolization of Stachybotrys chartarum for modeling pulmonary inhalation exposure

Objective: Stachybotrys chartarum is a hydrophilic fungal species commonly found as a contaminant in water-damaged building materials. Although several studies have suggested that S. chartarum exposure elicits a variety of adverse health effects, the ability to characterize the pulmonary immune responses to exposure is limited by delivery methods that do not replicate environmental exposure. This study aimed to develop a method of S. chartarum aerosolization to better model inhalation exposures. Materials and methods: An acoustical generator system (AGS) was previously developed and utilized to aerosolize and deliver fungal spores to mice housed in a multi-animal nose-only exposure chamber. In this study, methods for cultivating, heat-inactivating, and aerosolizing two macrocyclic trichothecene-producing strains of S. chartartum using the AGS are described. Results and discussion: In addition to conidia, acoustical generation of one strain of S. chartarum resulted in the aerosolization of fungal fragments (<2 µm aerodynamic diameter) derived from conidia, phialides, and hyphae that initially comprised 50% of the total fungal particle count but was reduced to less than 10% over the duration of aerosolization. Acoustical generation of heat-inactivated S. chartarum did not result in a similar level of fragmentation. Delivery of dry, unextracted S. chartarum using these aerosolization methods resulted in pulmonary inflammation and immune cell infiltration in mice inhaling viable, but not heat-inactivated S. chartarum. Conclusions: These methods of S. chartarum growth and aerosolization allow for the delivery of fungal bioaerosols to rodents that may better simulate natural exposure within water-damaged indoor environments.

Exploiting the Advantages of Molecular Tools for the Monitoring of Fungal Indoor Air Contamination: First Detection of Exophiala jeanselmei in Indoor Air of Air-Conditioned Offices

Today, indoor air pollution is considered a public health issue. Among the impacting pollutants, indoor airborne fungi are increasingly highlighted. Most of the monitoring protocols are culture-based, but these are unable to detect the uncultivable and/or dead fraction or species suppressed by fast-growing fungi, even though this fraction could impact health. Among the contaminants suspected to be part of this fraction, Exophiala jeanselmei is an interesting case study. Known to be pathogenic, this black yeast grows in humid environments such as air-conditioning systems, where it has been previously detected using classical culture-based methods. However, until now, this fungus was never detected in indoor air in contact with these air-conditioning systems. This study shows the first detection of E. jeanselmei in indoor air collected from offices in contact with contaminated air-conditioning reservoirs. While its presence in indoor air could not be demonstrated with culture-based methods, it was found by real-time PCR and massive parallel sequencing. The latter also allowed obtaining a broader view on the fungal diversity in the tested samples. Similar approaches were applied on water samples collected from the conditioning reservoirs to trace the source of contamination. The comparison of results obtained with both methods confirmed that the molecular tools could improve indoor air monitoring, especially of dead and/or uncultivable contaminants or when competition between species could occur.

Fungal aerosol composition in moldy basements

Experimental aerosolization studies revealed that fungal fragments including small fragments in the submicrometer size are released from fungal cultures and have been suggested to represent an important fraction of overall fungal aerosols in indoor environments. However, their prevalence indoors and outdoors remains poorly characterized. Moldy basements were investigated for airborne fungal particles including spores, submicron fragments, and larger fragments. Particles were collected onto poly-L-lysine-coated polycarbonate filters and qualitatively and quantitatively analyzed using immunogold labeling combined with field emission scanning electron microscopy. We found that the total fungal aerosol levels including spores, submicrometer, and larger fragments in the moldy basements (median: 80 × 10³  m^-3 ) were not different from that estimated in control basements (63 × 10³  m^-3 ) and outdoor (90 × 10³  m^-3 ). However, mixed effect modeling of the fungal aerosol composition revealed that the fraction of fragments increased significantly in moldy basements, versus the spore fraction that increased significantly in outdoor air. These findings provide new insight on the compositional variation of mixed fungal aerosols in indoor as compared to outdoor air. Our results also suggest that further studies, aiming to investigate the role of fungal aerosols in the fungal exposure-disease relationships, should consider the mixed composition of various types of fungal particles.

Fungal Fragments and Fungal Aerosol Composition in Sawmills

Assessment of exposure to fungi has commonly been limited to fungal spore measurements that have shown associations between fungi and development or exacerbation of different airway diseases. Because large numbers of submicronic fragments can be aerosolized from fungal cultures under laboratory conditions, it has been suggested that fungal exposure is more complex and higher than that commonly revealed by spore measurements. However, the assessment of fungal fragments in complex environmental matrix remain limited due to methodological challenges. With a recently developed immunolabeling method for field emission scanning electron microscope (FESEM), we could assess the complex composition of fungal aerosols present in personal thoracic samples collected from two Norwegian sawmills. We found that large fungal fragments (length >1 µm) dominated the fungal aerosols indicating that the traditional monitoring approach of spores severely underestimate fungal exposure. The composition of fungal aerosols comprised in average 9% submicronic fragments, 62% large fragments, and 29% spores. The average concentrations of large and submicronic fragments (0.2–1 µm) were 3 × 10⁵ and 0.6 × 10⁵ particles m⁻³, respectively, and correlated weakly with spores (1.4 × 10⁵ particles m⁻³). The levels of fragments were 2.6 times higher than the average spore concentration that was close to the proposed hazardous level of 10⁵ spores per m³. The season influenced significantly the fungal aerosol concentrations but not the composition. Furthermore, the ratio of spores in the heterogeneous fungal aerosol composition was significantly higher in saw departments as compared to sorting of green timber departments where the fungal fragments were most prevalent. Being the dominating particles of fungal aerosols in sawmills, fungal fragments should be included in exposure-response studies to elucidate their importance for health impairments. Likewise, the use of fungal aerosol composition in such studies should be considered.

Bedroom Allergen Exposure Beyond House Dust Mites

PURPOSE OF REVIEW

The review provides insight into recent findings on bedroom allergen exposures, primarily focusing on pet, pest, and fungal exposures.

RECENT FINDINGS

Large-scale studies and improved exposure assessment technologies, including measurement of airborne allergens and of multiple allergens simultaneously, have extended our understanding of indoor allergen exposures and their impact on allergic disease. Practical, streamlined methods for exposure reduction have shown promise in some settings, and potential protective effects of early-life exposures have been further elucidated through the investigation of specific bacterial taxa. Advances in molecular allergology have yielded novel data on sensitization profiles and cross-reactivity. The role of indoor allergen exposures in allergic disease is complex and remains incompletely understood. Advancing our knowledge of various co-exposures, including the environmental and host microbiome, that interact with allergens in early life will be crucial for the development of efficacious interventions to reduce the substantial economic and social burden of allergic diseases including asthma.

Characterization and pro-inflammatory responses of spore and hyphae samples from various mold species

Mold particles from Aspergillus fumigatus, Penicillium chrysogenum, Aspergillus versicolor, and Stachybotrys chartarum have been linked to respiratory-related diseases. We characterized X-ray-inactivated spores and hyphae fragments from these species by number of particles, morphology, and mycotoxin, β-glucan and protease content/activity. The pro-inflammatory properties of mold particles were examined in human bronchial epithelial cells (BEAS-2B) and THP-1 monocytes and phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1. Spores from P. chrysogenum and S. chartarum contained some hyphae fragments, whereas the other preparations contained either spores or hyphae. Each mold species produced mainly one gelatin-degrading protease that was either of the metallo- or serine type, while one remains unclassified. Mycotoxin levels were generally low. Detectable levels of β-glucans were found mainly in hyphae particle preparations. PMA-differentiated THP-1 macrophages were by far the most sensitive model with effects in the order of 10 ng/cm² . Hyphae preparations of A. fumigatus and P. chrysogenum were more potent than respective spore preparations, whereas the opposite seems to be true for A. versicolor and S. chartarum. Hyphae fragments of A. fumigatus, P. chrysogenum, and A. versicolor enhanced the release of metalloprotease (proMMP-9) most markedly. In conclusion, species, growth stage, and characteristics are all important factors for pro-inflammatory potential.