Fungal and bacterial growth in floor dust at elevated relative humidity levels

Predicting how varying moisture conditions impact the microbiome of dust collected from the International Space Station

BACKGROUND

The commercialization of space travel will soon lead to many more people living and working in unique built environments similar to the International Space Station, which is a specialized closed environment that contains its own indoor microbiome. Unintended microbial growth can occur in these environments as in buildings on Earth from elevated moisture, such as from a temporary ventilation system failure. This growth can drive negative health outcomes and degrade building materials. We need a predictive approach for modeling microbial growth in these critical indoor spaces.

RESULTS

Here, we demonstrate that even short exposures to varying elevated relative humidity can facilitate rapid microbial growth and microbial community composition changes in dust from spacecraft. We modeled fungal growth in dust from the International Space Station using the time-of-wetness framework with activation and deactivation limited growth occurring at 85% and 100% relative humidity, respectively. Fungal concentrations ranged from an average of 4.4 × 106 spore equivalents per milligram of dust in original dust with no exposure to relative humidity to up to 2.1 × 1010 when exposed to 100% relative humidity for 2 weeks. As relative humidity and time-elevated increased, fungal diversity was significantly reduced for both alpha (Q < 0.05) and beta (R2 = 0.307, P = 0.001) diversity metrics. Bacteria were unable to be modeled using the time-of-wetness framework. However, bacterial communities did change based on constant relative humidity incubations for both beta (R2 = 0.22, P = 0.001) and alpha diversity decreasing with increasing moisture starting at 85% relative humidity (Q < 0.05).

CONCLUSION

Our results demonstrate that moisture conditions can be used to develop and predict changes in fungal growth and composition onboard human-occupied spacecraft. This predictive model can be expanded upon to include other spacecraft environmental factors such as microgravity, elevated carbon dioxide conditions, and radiation exposure. Understanding microbial growth in spacecraft can help better protect astronaut health, fortify spacecraft integrity, and promote planetary protection as human activity increases in low-Earth orbit, the moon, Mars, and beyond. Video Abstract.

Longitudinal Analysis of the Microbial Community on the Surface of Bloodstains Under Different Environmental Conditions in Areas with Minimal Human Interference

The association between human metabolites and the environmental microbiome has primarily been investigated in relation to disease. In this study, the associations between environmental conditions and microbial communities on the surface of bloodstains were analyzed from a forensic science approach. The composition of microbial communities can be affected by numerous variables. After exposing bloodstains to two different environments with limited airflow and human interference, the microbial communities of the bloodstain surfaces were subjected to longitudinal analysis. Various microbes showed increasing or decreasing trends at the phylum and species level. The microbes identified in this study are usually found in soil, freshwater, and seawater and are known to exhibit unique properties, such as sporulation. Longitudinal variation in temperature and humidity were associated with various changes and correlations with the blood surface microbial community. Understanding these changes could introduce a new perspective to forensic science and could be used to develop a forensic tool used at crime scenes to analyze blood stains in more detail.

Synergistic antibacterial effect and mechanism between Cu2O nanoparticles and quaternary ammonium salt in moisture-curable acrylic coatings

Combining with various antibacterial mechanisms is the preferred strategy to fabricate coatings with effective antibacterial performance. Herein, Cu2O nanoparticles and dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride, a kind of quaternary ammonium salt (QAS), were simultaneously incorporated into a moisture-curable acrylic resin in order to achieve both contact-killing and release-killing abilities for antibacterial coatings. The surface morphology, surface composition and basic properties of the coatings were thoroughly characterized. The antibacterial performance of the coatings was determined by in-vitro bacteriostatic test. Under the constant total mass fraction of antibacterial agents, both Cu2O and QAS content possessed the highest value on the coating surface at Cu2O/QAS mass ratio of 1:1, and correspondingly, the coatings reached sterilizing rate above 99 % against both E. coli and S. loihica, indicating the existence of synergistic effect between Cu2O and QAS. The synergistic antibacterial mechanism of the coatings involved two aspects. Firstly, the combination of contact-killing and release-killing biocides resulted in high bactericidal and antibiofilm activity against different bacteria. Further, the grafting of QAS molecules on the surface of Cu2O particles brought about the spontaneous migration of nanoparticles to the coating surface. The interaction between Cu2O and QAS also inhibited the phase separation of QAS and prolonged the release of Cu2+ at the same time. The coatings, therefore, exhibited stable antibacterial performance at varied service conditions.

Fungal diversity differences in the indoor dust microbiome from built environments on earth and in space

Human occupied built environments are no longer confined to Earth. In fact, there have been humans living and working in low-Earth orbit on the International Space Station (ISS) since November 2000. With NASA's Artemis missions and the age of commercial space stations set to begin, more human-occupied spacecraft than ever will be in Earth's orbit and beyond. On Earth and in the ISS, microbes, especially fungi, can be found in dust and grow when unexpected, elevated moisture conditions occur. However, we do not yet know how indoor microbiomes in Earth-based homes and in the ISS differ due to their unique set of environmental conditions. Here we show that bacterial and fungal communities are different in dust collected from vacuum bags on Earth and the ISS, with Earth-based homes being more diverse (465 fungal OTUs and 237 bacterial ASVs) compared to the ISS (102 fungal OTUs and 102 bacterial ASVs). When dust from these locations were exposed to varying equilibrium relative humidity conditions (ERH), there were also significant fungal community composition changes as ERH and time elevated increased (Bray Curtis: R2 = 0.35, P = 0.001). These findings can inform future spacecraft design to promote healthy indoor microbiomes that support crew health, spacecraft integrity, and planetary protection.

Effects of surface-attached durations, nutrients, and relative humidity on the resuspension of bacteria during human walking

Resuspension caused by human walking activities is an important source of indoor bioaerosols and has been associated with health effects such as allergies and asthma. However, it is unknown whether inhalation of resuspended bioaerosols is an important exposure pathway for airborne infection. Also, crucial factors influencing the resuspension of settled microbes have not been quantified. In this study, we experimentally investigated the resuspension of culturable bacteria from human-stepping on polyvinyl chloride (PVC) flooring under different conditions. We determined the bacterial resuspension emission factor (ER), a normalized resuspension parameter for the ratio of resuspended mass in the air to the mass of settled particles, for two common bacteria, Escherichia coli and Salmonella enterica. The investigation involved varying factors such as microbial surface-attached durations (0, 1, 2, and 3 days), the absence or presence of nutrients on flooring surfaces, and changes in relative humidity (RH) (35%, 65%, and 85%). The results showed that, in the absence of nutrients, the highest ER values for E. coli and S. enterica were 3.8 × 10-5 ± 5.2 × 10-6 and 5.3 × 10-5 ± 6.0 × 10-6, respectively, associated with surface-attached duration of 0 days. As the surface-attached duration increased from 0 to 3 days, ER values decreased by 92% and 84% for E. coli and S. enterica, respectively. In addition, we observed that ER values decreased with the increasing RH, which is consistent with particle adhesion theory. This research offers valuable insights into microbial resuspension during human walking activities and holds the potential for assisting in the assessment and estimation of risks related to human exposure to bioaerosols.

Exploring the key deteriorative microorganisms on ancient ivories unearthed from the Sanxingdui Ruins site during temporary cold storage

Introduction

The ancient ivories unearthed from the Sanxingdui Ruins site are valuable cultural relics, however, the microbial biodeterioration on ivories during temporary cold storage poses a great threat to their later long-term preservation.

Methods

Here, the combination of high-throughput sequencing and biochemical assays was applied for the in-depth investigation of the key deteriorative microorganisms colonizing on the ivories and the tracing of their origin, as well as the assessment of the ethanol disinfection impact on the microbial communities on ivories.

Results

It was observed that the surfaces of ivories were scattered by the fungal patches of white, dark grey, and hedge green colors during cold storage. The high-throughput sequencing results showed that the genera Mortierella (38.51%), Ilyonectria (14.43%), Penicillium (1.15%), and Aspergillus (1.09%) were the dominant fungi, while Pseudomonas (22.63%), Sphingopyxis (3.06%), and Perlucidibaca (2.92%) were the dominant bacteria on ivories. The isolated Aspergillus A-2 resulted in the highest amount of calcium releasing from the degradation of hydroxyapatite (HAP), the main component of ivory, by the organic acids produced, including oxalic acid and citric acid. The fast expectation-maximization for microbial source tracking (FEAST) analysis revealed that the majority of the fungi (57.45%) and bacteria (71.84%) colonizing on the ivories were derived from the soils surrounding ivories in the sacrifice pits, indicating soils as the primary source for the spoilage microbes growing on ivories. The dominant strains could degrade cellulose, the key components of wet cotton towels commonly applied on ivories for moisture maintenance, aiding the spoilage microbes colonizing on ivories. Notably, the ivory disinfection with 75% ethanol during the cleansing significantly decreased the relative abundance of the dominant genera of Ilyonectria, Aspergillus, and Pseudomonas, with Mortierella becoming the dominant one on ivories.

Discussion

Together, the fungi, particularly Aspergillus and Penicillium, played a significant role in the microbial biodeterioration of unearthed ancient ivories by producing the organic acids. These results may improve the control of the microbial biodeterioration and develop more efficient strategies for the long-time conservation of unearthed ancient ivories and other cultural relics.

Environmental processes and health implications potentially mediated by dust-borne bacteria

Understanding microbial migration and survival mechanisms in dust events (DEs) can elucidate genetic and metabolic exchange between environments and help predict the atmospheric pathways of ecological and health-related microbial stressors. Dust-borne microbial communities have been previously characterized, but the impact and interactions between potentially active bacteria within transported communities remain limited. Here, we analysed samples collected during DEs in Israel, using amplicon sequencing of the 16S rRNA genes and transcripts. Different air trajectories and wind speeds were associated not only with the genomic microbial community composition variations but also with specific 16S rRNA bacterial transcripts. Potentially active dust-borne bacteria exhibited positive interactions, including carbon and nitrogen cycling, biotransformation of heavy metals, degradation of organic compounds, biofilm formation, and the presence of pathogenic taxa. This study provides insights into the potential interactive relationships and survival strategies of microorganisms within the extreme dust environment.

Association of exposure to indoor molds and dampness with allergic diseases at water-damaged dwellings in Korea

This study aims to characterize levels of molds, bacteria, and environmental pollutants, identify the associations between indoor mold and dampness exposures and childhood allergic diseases, including asthma, allergic rhinitis, atopic dermatitis, using three different exposure assessment tools. A total of 50 children with their parents who registered in Seoul and Gyeonggi-do in Korea participated in this study. We collated the information on demographic and housing characteristics, environmental conditions, and lifestyle factors using the Korean version of the International Study of Asthma and Allergies in Childhood questionnaire. We also collected environmental monitoring samples of airborne molds and bacteria, total volatile organic compounds, formaldehyde, and particulate matter less than 10 µm. We evaluated and determined water damage, hidden dampness, and mold growth in dwellings using an infrared (IR) thermal camera and field inspection. Univariate and multivariate regression analyses were performed to evaluate the associations between prevalent allergic diseases and exposure to indoor mold and dampness. Indoor mold and bacterial levels were related to the presence of water damage in dwellings, and the mean levels of indoor molds (93.4 ± 73.5 CFU/m3) and bacteria (221.5 ± 124.2 CFU/m3) in water-damaged homes were significantly higher than those for molds (82.0 ± 58.7 CFU/m3) and for bacteria (152.7 ± 82.1 CFU/m3) in non-damaged dwellings (p < 0.05). The crude odds ratios (ORs) of atopic dermatitis were associated with < 6th floor (OR = 3.80), and higher indoor mold (OR = 6.42) and bacterial levels (OR = 6.00). The crude ORs of allergic diseases, defined as a group of cases who ever suffered from two out of three allergic diseases, e.g., asthma and allergic rhinitis, and allergic rhinitis were also increased by 3.8 and 9.3 times as large, respectively, with water damage (+) determined by IR camera (p < 0.05). The adjusted OR of allergic rhinitis was significantly elevated by 10.4 times in the water-damaged dwellings after adjusting age, sex, and secondhand smoke. Therefore, a longitudinal study is needed to characterize dominant mold species using DNA/RNA-based sequencing techniques and identify a causal relationship between mold exposure and allergic diseases in the future.

Fungal diversity in homes and asthma morbidity among school-age children in New York City

BACKGROUND

Asthma development has been inversely associated with exposure to fungal diversity. However, the influence of fungi on measures of asthma morbidity is not well understood.

OBJECTIVES

This study aimed to test the hypothesis that fungal diversity is inversely associated with neighborhood asthma prevalence and identify specific fungal species associated with asthma morbidity.

METHODS

Children aged 7-8 years (n = 347) living in higher (11-18%) and lower (3-9%) asthma prevalence neighborhoods were recruited within an asthma case-control study. Fungal communities were analyzed from floor dust using high-throughput DNA sequencing. A subset of asthmatic children (n = 140) was followed to age 10-11 to determine asthma persistence.

RESULTS

Neighborhood asthma prevalence was inversely associated with fungal species richness (P = 0.010) and Shannon diversity (P = 0.059). Associations between neighborhood asthma prevalence and diversity indices were driven by differences in building type and presence of bedroom carpet. Among children with asthma at age 7-8 years, Shannon fungal diversity was inversely associated with frequent asthma symptoms at that age (OR 0.57, P = 0.025) and with asthma persistence to age 10-11 (OR 0.48, P = 0.043). Analyses of individual fungal species did not show significant associations with asthma outcomes when adjusted for false discovery rates.

DISCUSSION

Lower fungal diversity was associated with asthma symptoms in this urban setting. Individual fungal species associated with asthma morbidity were not detected. Further research is warranted into building type, carpeting, and other environmental characteristics which influence fungal exposures in homes.

Environmental determinants and demographic influences on global urban microbiomes, antimicrobial resistance and pathogenicity

Urban microbiome plays crucial roles in human health and are related to various diseases. The MetaSUB Consortium has conducted the most comprehensive global survey of urban microbiomes to date, profiling microbial taxa/functional genes across 60 cities worldwide. However, the influence of environmental/demographic factors on urban microbiome remains to be elucidated. We collected 35 environmental and demographic characteristics to examine their effects on global urban microbiome diversity/composition by PERMANOVA and regression models. PM10 concentration was the primary determinant factor positively associated with microbial α-diversity (observed species: p = 0.004, β = 1.66, R2 = 0.46; Fisher's alpha: p = 0.005, β = 0.68, R2 = 0.43), whereas GDP per capita was negatively associated (observed species: p = 0.046, β = -0.70, R2 = 0.10; Fisher's alpha: p = 0.004, β = -0.34, R2 = 0.22). The β-diversity of urban microbiome was shaped by seven environmental characteristics, including Köppen climate type, vegetation type, greenness fraction, soil type, PM2.5 concentration, annual average precipitation and temperature (PERMANOVA, p < 0.001, R2 = 0.01-0.06), cumulatively accounted for 20.3% of the microbial community variance. Canonical correspondence analysis (CCA) identified microbial species most strongly associated with environmental characteristic variation. Cities in East Asia with higher precipitation showed an increased abundance of Corynebacterium metruchotii, and cities in America with a higher greenness fraction exhibited a higher abundance of Corynebacterium casei. The prevalence of antimicrobial resistance (AMR) genes were negatively associated with GDP per capita and positively associated with solar radiation (p < 0.005). Total pathogens prevalence was positively associated with urban population and negatively associated with average temperature in June (p < 0.05). Our study presents the first comprehensive analysis of the influence of environmental/demographic characteristics on global urban microbiome. Our findings indicate that managing air quality and urban greenness is essential for regulating urban microbial diversity and composition. Meanwhile, socio-economic considerations, particularly reducing antibiotic usage in regions with lower GDP, are paramount in curbing the spread of antimicrobial resistance in urban environments.

Potential airborne human pathogens: A relevant inhabitant in built environments but not considered in indoor air quality standards

Potential airborne human pathogens (PAHPs) may be a relevant component of the air microbiome in built environments. Despite that PAHPs can cause infections, particularly in immunosuppressed patients at medical centers, they are scarcely considered in standards of indoor air quality (IAQ) worldwide. Here, we reviewed the current information on microbial aerosols (bacteria, fungal and viruses) and PAHPs in different types of built environments (e.g., medical center, industrial and non-industrial), including the main factors involved in their dispersion, the methodologies used in their study and their associated biological risks. Our analysis identified the human occupancy and ventilation systems as the primary sources of dispersal of microbial aerosols indoors. We also observed temperature and relative humidity as relevant physicochemical factors regulating the dispersion and viability of some PAHPs. Our analysis revealed that some PAHPs can survive and coexist in different environments while other PAHPs are limited or specific for an environment. In relation to the methodologies (conventional or molecular) the nature of PAHPs and sampling type are pivotal. In this context, indoors air-borne viruses are the less studies because their small size, environmental lability, and absence of efficient sampling techniques and universal molecular markers for their study. Finally, it is noteworthy that PAHPs are not commonly considered and included in IAQ standards worldwide, and when they are included, the total abundance is the single parameter considered and biological risks is excluded. Therefore, we propose a revision, design and establishment of public health policies, regulations and IAQ standards, considering the interactions of diverse factors, such as nature of PAHPs, human occupancy and type of built environments where they develop.

Xerophilic fungi contaminating historically valuable easel paintings from Slovenia

Historically valuable canvas paintings are often exposed to conditions enabling microbial deterioration. Painting materials, mainly of organic origin, in combination with high humidity and other environmental conditions, favor microbial metabolism and growth. These preconditions are often present during exhibitions or storage in old buildings, such as churches and castles, and also in museum storage depositories. The accumulated dust serves as an inoculum for both indoor and outdoor fungi. In our study, we present the results on cultivable fungi isolated from 24 canvas paintings, mainly exhibited in Slovenian sacral buildings, dating from the 16th to 21st centuries. Fungi were isolated from the front and back of damaged and undamaged surfaces of the paintings using culture media with high- and low-water activity. A total of 465 isolates were identified using current taxonomic DNA markers and assigned to 37 genera and 98 species. The most abundant genus was Aspergillus, represented by 32 species, of which 9 xerophilic species are for the first time mentioned in contaminated paintings. In addition to the most abundant xerophilic A. vitricola, A. destruens, A. tardicrescens, and A. magnivesiculatus, xerophilic Wallemia muriae and W. canadensis, xerotolerant Penicillium chrysogenum, P. brevicompactum, P. corylophilum, and xerotolerant Cladosporium species were most frequent. When machine learning methods were used to predict the relationship between fungal contamination, damage to the painting, and the type of material present, proteins were identified as one of the most important factors and cracked paint was identified as a hotspot for fungal growth. Aspergillus species colonize paintings regardless of materials, while Wallemia spp. can be associated with animal fat. Culture media with low-water activity are suggested in such inventories to isolate and obtain an overview of fungi that are actively contaminating paintings stored indoors at low relative humidity.

Bacterial Flora on Mist Outlet Surfaces in 4D Theaters and Suspended Particle Concentration Characteristics during 4D Movie Screenings

In this study, we measured suspended particle concentrations during the screening of 4D movies (3 screens and 15 movies) and 2D movies (9 screens and 9 movies) in 3 movie theaters to obtain a more detailed understanding of the situation of suspended particle concentrations and adherent bacterial flora in 4D movie theaters, which have been introduced in increasing numbers in recent years. The adherent bacterial flora on the floor and mist outlet surfaces in the 4D movie theaters were collected and analyzed. During the movie showings, the concentrations of suspended particles in 4D movie theaters were significantly higher than those in 2D movie theaters (p < 0.001). A significant increase in suspended particle concentrations due to 4D movie effects was also observed. The results of the α-diversity and β-diversity analyses indicate that the bacterial flora on the surfaces of mist outlets in 4D movie theaters are similar. Moreover, there are many closely related species, and the bacterial flora are rich and contain rare bacterial species. Many of the bacterial genera that are dominant in 4D theaters are suited to aqueous environments, and bacteria in the water supply system may have an impact on the indoor environment.

Lignin Nanoparticles for Enhancing Physicochemical and Antimicrobial Properties of Polybutylene Succinate/Thymol Composite Film for Active Packaging

The natural abundance, polymer stability, biodegradability, and natural antimicrobial properties of lignin open a wide range of potential applications aiming for sustainability. In this work, the effects of 1% (w/w) softwood kraft lignin nanoparticles (SLNPs) on the physicochemical properties of polybutylene succinate (PBS) composite films were investigated. Incorporation of SLNPs into neat PBS enhanced T_d from 354.1 °C to 364.7 °C, determined through TGA, whereas T_g increased from -39.1 °C to -35.7 °C while no significant change was observed in T_m and crystallinity, analyzed through DSC. The tensile strength of neat PBS increased, to 35.6 MPa, when SLNPs were added to it. Oxygen and water vapor permeabilities of PBS with SLNPs decreased equating to enhanced barrier properties. The good interactions among SLNPs, thymol, and PBS matrix, and the high homogeneity of the resultant PBS composite films, were determined through FTIR and FE-SEM analyses. This work revealed that, among the PBS composite films tested, PBS + 1% SLNPs + 10% thymol showed the strongest microbial growth inhibition against Colletotrichum gloeosporioides and Lasiodiplodia theobromae, both in vitro, through a diffusion method assay, and in actual testing on active packaging of mango fruit (cultivar "Nam Dok Mai Si Thong"). SLNPs could be an attractive replacement for synthetic substances for enhancing polymer properties without compromising the biodegradability of the resultant material, and for providing antimicrobial functions for active packaging applications.

Temporary establishment of bacteria from indoor plant leaves and soil on human skin

BACKGROUND

Plants are found in a large percentage of indoor environments, yet the potential for bacteria associated with indoor plant leaves and soil to colonize human skin remains unclear. We report results of experiments in a controlled climate chamber to characterize bacterial communities inhabiting the substrates and leaves of five indoor plant species, and quantify microbial transfer dynamics and residence times on human skin following simulated touch contact events. Controlled bacterial propagule transfer events with soil and leaf donors were applied to the arms of human occupants and repeatedly measured over a 24-h period using 16S rRNA gene amplicon sequencing.

RESULTS

Substrate samples had greater biomass and alpha diversity compared to leaves and baseline skin bacterial communities, as well as dissimilar taxonomic compositions. Despite these differences in donor community diversity and biomass, we observed repeatable patterns in the dynamics of transfer events. Recipient human skin bacterial communities increased in alpha diversity and became more similar to donor communities, an effect which, for soil contact only, persisted for at least 24 h. Washing with soap and water effectively returned communities to their pre-perturbed state, although some abundant soil taxa resisted removal through washing.

CONCLUSIONS

This study represents an initial characterization of bacterial relationships between humans and indoor plants, which represent a potentially valuable element of biodiversity in the built environment. Although environmental microbiota are unlikely to permanently colonize skin following a single contact event, repeated or continuous exposures to indoor biodiversity may be increasingly relevant for the functioning and diversity of the human microbiome as urbanization continues.

Spring is associated with increased total and allergenic fungal concentrations in house dust from a pediatric asthma cohort in New York City

Introduction

Asthma and allergy symptoms vary seasonally due to exposure to environmental sources of allergen, including fungi. However, we need an improved understanding of seasonal influence on fungal exposures in the indoor environment. We hypothesized that concentrations of total fungi and allergenic species in vacuumed dust vary significantly by season.

Objective

Assess seasonal variation of indoor fungi with greater implications related to seasonal asthma control.

Methods

We combined next-generation sequencing with quantitative polymerase chain reaction (qPCR) to measure concentrations of fungal DNA in indoor floor dust samples (n = 298) collected from homes participating in the New York City Neighborhood Asthma and Allergy Study (NAAS).

Results

Total fungal concentration in spring was significantly higher than the other three seasons (p ≤ 0.005). Mean concentrations for 78% of fungal species were elevated in the spring (26% were significantly highest in spring, p < 0.05). Concentrations of 8 allergenic fungal species were significantly (p < 0.5) higher in spring compared to at least two other seasons. Indoor relative humidity and temperature were significantly highest in spring (p < 0.05) and were associated with total fungal concentration (R2 = 0.049, R2 = 0.11, respectively).

Conclusion

There is significant seasonal variation in total fungal concentration and concentration of select allergenic species. Indoor relative humidity and temperature may underlie these associations.

Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents' source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field.

The Effects of Ventilation, Humidity, and Temperature on Bacterial Growth and Bacterial Genera Distribution

BACKGROUND

Bacteria are readily nourished in airtight environments with high humidity, such as storage cabinets, clothing closets, and corners, where ventilation is normally low and humidity is high.

OBJECTIVES

We characterized the role of humidity and ventilation in bacterial growth and genus distribution at different temperatures (26 °C and 34 °C).

METHODS

Fresh pork, which was used as the substrate for bacterial culture, was placed in storage cabinets. Bacterial growth and genera distribution on the surface of pork placed in a storage cabinet under different temperatures (26 °C and 34 °C); relative humidity levels (RH: 50%, 70%, 90%); and ventilation conditions (no ventilation and low, medium, and high levels of ventilation) were assessed by rDNA sequencing.

RESULTS

Increased ventilation and reduced humidity significantly decreased bacterial growth at 26 °C and 34 °C. The contribution of increased ventilation to the reduction in bacterial growth exceeded that of decreased humidity. Ventilation had the greatest effect on reducing bacterial growth compared to the unventilated conditions at 70% RH. At 34 °C, medium and high levels of ventilation were required to reduce bacterial growth. High temperatures greatly increased bacterial growth, but ventilation could reduce the degree of this increase.

Diurnal trends of indoor and outdoor fluorescent biological aerosol particles in a tropical urban area

We evaluated diurnal trends of size-resolved indoor and outdoor fluorescent biological airborne particles (FBAPs) and their contributions to particulate matter (PM) within 0.5-20 μm. After a ten-week continuous sampling via two identical wideband integrated bioaerosol sensors, we found that both indoor and outdoor diurnal trends of PM were driven by its bioaerosol component. Outdoors, the median [interquartile range] FBAP mass concentration peaked at 8.2 [5.8-9.9] μg/m³ around sunrise and showed a downtrend from 6:00 to 18:00 during the daytime and an uptrend during the night. The nighttime FBAP level was 1.8 [1.4-2.2] times higher than that during the daytime, and FBAPs accounted for 45 % and 56 % of PM during daytime and nighttime, respectively. Indoors, the rise in concentrations of FBAPs smaller than 1 μm coincided with the starting operation of the heating, ventilation, and air conditioning (HVAC) system at 6:00, and the concentration peaked at 8:00 and dropped to the daily average by noontime. This indicated that the starting operation of the HVAC system dislodged the overnight settled and accumulated fine bioaerosols into the indoor environment. For particles larger than 1 μm, the variation of mass concentration was driven by occupancy. Based on regression modeling, the contributions of indoor PM, non-FBAP, and FBAP sources to indoor mass concentrations were estimated to be 93 %, 67 %, and 97 % during the occupied period.

Bacterial Communities in Various Parts of Air-Conditioning Units in 17 Japanese Houses

HVAC systems have a significant impact on the indoor environment, and microbial contamination in HVAC systems has a significant effect on the indoor air quality. In this study, to gain a better understanding of the microbial contamination inside ACs, we used NGS to analyze the 16S rRNA gene of bacteria adhering to AC filters, cooling coils, fans, and air outlet surfaces. The five phyla in terms of the highest relative abundance were Proteobacteria, Firmicutes, Actinobacteria, Cyanobacteria, and Bacteroidetes. The surface of an AC filter provides a history of indoor airborne bacterial contamination, and of the 10 bacterial genera we detected with the highest abundance (in the following order: Pseudomonas > Staphylococcus > Paracoccus > Corynebacterium > Acinetobacter > Streptococcus > Methylobacterium > Enhydrobacter > Sphingomonas > Actinotignum) on the filter surface, the top 6 genera were Gram-negative bacteria. Furthermore, the seventh-most abundant genus adhering to the filter surface (Methylobacterium) was the second-most abundant genus on the cooling coil and fan, and the ninth-most abundant genus on the air filter (Sphingomonas) was the third-most abundant genus on the cooling coil. Various factors impact the bacterial flora inside AC units, including the location of the house, AC unit usage, and occupant activity.

Dust Deposition and Associated Heavy Metal Contamination in the Neighborhood of a Cement Production Plant at Konongo, Ghana

The release of harmful particles from industries is one of the important sources of environmental pollution worldwide. The goal of this study was to determine the amounts of dust deposition and heavy metal pollution in the soils surrounding a cement mill in Konongo, Ghana. Topsoils (0-10 cm) were sampled at the four geographical axes of the factory within a radius of 400 m, while at the same time, about 500 g of cement was sampled with a hand trowel. A Frisbee dust sampler was used to examine the levels of dust depositions at the various geographical axes of the factory. The heavy metals such as cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), and lead (Pb) were measured in a total of 20 soil samples using atomic absorption spectroscopy (AAS). The results obtained for climatic elements such as wind speed and direction, temperature, and relative humidity were 2.25, 25.7, and 49.5 m3/s, respectively. The average deposition of dust within the study period using the geographical axis indicated that the southern axis recorded the highest dust accumulation with a mean of 60.2 g/m2 per month. The mean concentrations of metals at the various axes were 1.04 mg/kg, 4.78 mg/kg, 8.95 mg/kg, 9.30 mg/kg, and 18.4 mg/kg for Cd, Cr, Cu, Zn, and Pb, respectively. The concentration of chemical components investigated in the soil was below the WHO/FAO standard, except for Cd. The spatial distribution pattern of the examined heavy metals showed that Cd, Cr, and Cu represent possible sources of soil contaminants. According to the conclusions of this research, this paper suggests an approach to investigate the areas contaminated with heavy metals to call out the attention of local authorities to take action.

Season, Vegetation Proximity and Building Age Shape the Indoor Fungal Communities' Composition at City-Scale

Exposure to particular microbiome compositions in the built environment can affect human health and well-being. Identifying the drivers of these indoor microbial assemblages is key to controlling the microbiota of the built environment. In the present study, we used culture and metabarcoding of the fungal Internal Transcribed Spacer ribosomal RNA region to assess whether small-scale variation in the built environment influences the diversity, composition and structure of indoor air fungal communities between a heating and an unheated season. Passive dust collectors were used to collect airborne fungi from 259 dwellings representative of three major building periods and five building environments in one city-Lausanne (Vaud, Switzerland)-over a heating and an unheated period. A homogenous population (one or two people with an average age of 75 years) inhabited the households. Geographic information systems were used to assess detailed site characteristics (altitude, proximity to forest, fields and parks, proximity to the lake, and density of buildings and roads) for each building. Our analysis indicated that season was the factor that explained most of the variation in colonies forming unit (CFU) concentration and indoor mycobiome composition, followed by the period of building construction. Fungal assemblages were more diverse during the heating season than during the unheated season. Buildings with effective insulation had distinct mycobiome compositions from those built before 1975 - regardless of whether they were constructed with pre-1945 technology and materials or 1945 - 1974 ones. The urban landscape-as a whole-was a significant predictor of cultivable Penicillium load-the closer the building was to the lake, the higher the Penicillium load-but not of fungal community composition. Nevertheless, the relative abundance of eleven fungal taxa detected by metabarcoding decreased significantly with the urbanization gradient. When urban landscape descriptors were analyzed separately, the explanatory power of proximity to vegetation in shaping fungal assemblages become significant, indicating that land cover type had an influence on fungal community structure that was obscured by the effects of building age and sampling season. In conclusion, indoor mycobiomes are strongly modulated by season, and their assemblages are shaped by the effectiveness of building insulation, but are weakly influenced by the urban landscape.

Size distribution, community composition, and influencing factors of bioaerosols on haze and non-haze days in a megacity in Northwest China

Bioaerosols have become a major environmental concern in recent years. In this study, the diurnal variations and size distributions of bioaerosols, as well as airborne bacterial community compositions and their influencing factors on haze and non-haze days in Xi'an, China, were compared. The results indicated that the mean bacteria and fungi concentrations on non-haze days were 1.7 and 1.4 times of those on haze days, respectively, whereas the mean total airborne microbe (TAM) concentration was higher on haze days. Bacteria concentrations were the lowest in the afternoon, and the TAM concentration exhibited a bimodal distribution with two peaks coinciding with traffic rush hours. On haze days airborne fungi was mainly attached to PM_2.5, whereas bacteria and TAM were mainly distributed in coarse PM. The relative abundance of Chao1, Shannon and Simpson indices of bacterial communities were higher in the non-haze day samples, for the reason that high PM_2.5 levels with a large specific surface area may absorb more toxic and harmful substances on haze days, which should affect microbial growth. At the generic level, the relative abundance of Rhodococcus, Paracoccus, Acinetobacter, and Kocuria on haze days was higher than that on non-haze days, indicating a higher risk of contracting pathogenic pneumonia. The results of the redundancy analysis revealed that PM_2.5 and water-soluble inorganic ions (WSIIs, NO₃^-, SO₄²⁺, and NH₄⁺) strongly affected the bacterial communities on non-haze days, especially Acinetobacter. The atmospheric oxidation capacity (O_x) had a significant effect on bacterial communities during haze episodes, which were positively correlated with Paracoccus, Deinococcus, Sphingomonas, and Rubellimicrobium and were negatively correlated with Rhodococcus. These results provide valuable data to elucidate the formation and evolution of bioaerosol between haze and non-haze events and its potential threats to human health.

Characteristics of annual mold variations and association with childhood allergic symptoms/diseases via combining surveys and home visit measurements

The presence of dampness and visible molds leads to concerns of poor indoor air quality which has been consistently linked with increased exacerbation and development of allergy and respiratory diseases. Due to the limitations of epidemiological surveys, the actual fungal exposure characteristics in residences has not been sufficiently understood. This study aimed to characterize household fungal diversity and its annual temporal and spatial variations. We developed combined cross-sectional survey, repeated air sampling around a year, and DNA sequencing methods. The questionnaire survey was conducted in 2019, and 4943 valid cases were received from parents; a follow-up case-control study (11 cases and 12 controls) was designed, and onsite measurements of indoor environments were repeated in typical summer, transient season, and winter; dust from floor and beddings in children's room were collected and ITS based DNA sequencing of totally 68 samples was conducted. Results from 3361 children without changes to their residences since birth verified the significant associations of indoor dampness/mold indicators and prevalence of children-reported diseases, with increased adjusted odd ratios (aORs) >1 for studied asthma, wheeze, allergic rhinitis, and eczema. The airborne fungal concentrations from air sampling were higher than 1000 CFU/m³ in summer, regardless of indoors and outdoors, indicating an intermediate pollution level. The DNA sequencing for dust showed the Aspergillus was the predominant at genus level and the Aspergillus_penicillioides was the most common at species level; while the fungal community and composition varied significantly in different homes and seasons, according to α and β diversity analyses. The comprehensive research methods contribute to a holistic understanding of indoor fungal exposure, including the concentrations, seasonal variations, community, and diversity, and verifies the relations with children's adverse health outcomes. The study further elucidates the role of microbiome in human health, which helps setting health-protective thresholds and managing mold treatments in buildings, to promote indoor air quality and human well-beings.

Impact of mold growth on di(2-ethylhexyl) phthalate emission from moist wallpaper

Flood damage can increase indoor concentrations of di(2-ethylhexyl) phthalate (DEHP) and molds in households with wallpaper. Wallpaper water content can affect its DEHP emission into indoor environments; however, the influence of mold growth on this DEHP emission remains unclear. Here, we evaluated whether mold growth affects DEHP emission from moist wallpaper (moist WP). Experiments were conducted in glass chambers with wallpaper containing 12.7% (w/w) DEHP and a dust tray sample system at approximately 28 °C and 100% relative humidity (RH). The experimental groups were (1) moist WP, (2) moist WP + Aspergillus versicolor (AV), (3) moist WP + Cladosporium cladosporioides, (4) moist WP + Penicillium chrysogenum, and (5) moist WP + mold mixture. Mold growth on the wallpaper and DEHP emission into air and onto dust were analyzed at nine time-points over 30 days. Initially, the moist WP group emitted relatively high concentrations of DEHP into air, but after at least 8 days, the concentration of DEHP emitted by the mold-added groups exceeded that of the moist WP group. DEHP emission onto dust, especially from the moist WP group, increased considerably at day 15. During the experimental period, the moist WP (13.63 ± 4.67 μg) and moist WP + AV (13.93 ± 0.49 μg) groups emitted higher cumulative amounts of DEHP onto dust. During the 30-day experimental period, obvious mold growth occurred over days 15–30. Moreover, the moist WP group exhibited relatively higher and lower cumulative DEHP emission into air than the mold-added groups during days 2–10 (2.71 vs. 1.94–2.94 μg) and 15–30 (1.16 vs. 1.61–2.12), respectively; a contrasting trend was observed for cumulative DEHP emission onto dust. In conclusion, mold growth affects DEHP emission from water-damaged wallpaper, and the removal or cleaning of wet wallpaper, particularly those with visible mold growth, is critical from a public health perspective.

Mycobiota and the Contribution of Yeasts in Floor Dust of 50 Elementary Schools Characterized with Sequencing Internal Transcribed Spacer Region of Ribosomal DNA

The assemblage of fungi including unicellular yeasts in schools is understudied. We conducted an environmental study to characterize fungal communities in classroom floor dust. We collected 500 samples from 50 elementary schools in Philadelphia, PA, and evaluated room dampness/mold conditions. Genomic DNA from dust was extracted for internal transcribed spacer 1 Illumina MiSeq sequencing to identify operational taxonomic units (OTUs) organized from DNA sequences. Differential abundance analyses were performed to examine significant differences in abundance among groups. We identified 724 genera from 1490 OTUs. The genus Epicoccum was not diverse but the most abundant (relative abundance = 18.9%). Fungi were less diverse but most dissimilar in composition in the most water-damaged classrooms compared to the least water-damaged, indicating differential effects of individual classroom water-damage on fungal compositions. We identified 62 yeast genera, representing 19.6% of DNA sequences. Cyberlindnera was the most abundant (6.1%), followed by Cryptococcus, Aureobasidium, Rhodotorula, and Candida. The average relative abundance of yeasts tended to increase with increasing dampness and mold score and was significantly (p-value = 0.048) higher in the most water-damaged classrooms (22.4%) than the least water-damaged classrooms (18.2%). Our study suggests the need for further research on the potential health effects associated with exposures to yeasts in schools.

An Assessment of Airborne Bacteria and Fungi in the Female Dormitory Environment: Level, Impact Factors and Dose Rate

In this study, the levels of airborne bacteria and fungi were tested in a female dormitory room; the effects of heating, relative humidity and number of occupants on indoor microorganisms were analyzed and the dose rate of exposure to microbes was assessed. The bacterial and fungal concentrations in the room ranged from 100 to several thousand CFU/m³, and the highest counts were observed in the morning (930 ± 1681 CFU/m³). Staphylococcus spp. and Micrococcus spp. were found in the dormitory. When the heating was on, the total bacterial and fungal counts were lower than when there was no heating. Moreover, statistically significant differences were observed for bacterial concentrations during the morning periods between the times when there was no heating and the times when there was heating. The number of occupants had an obvious positive effect on the total bacterial counts. Moreover, RH had no correlation with the airborne fungi in the dormitory, statistically. Furthermore, the highest dose rate from exposure to bacteria and fungi was observed during sleeping hours. The dose rate from exposure to airborne microorganisms in the dormitory was associated with the activity level in the room. These results helped to elucidate the threat of bioaerosols to the health of female occupants and provide guidance for protective measures.

Aerosolization of fungal spores in indoor environments

Fungi in indoor environments can cause adverse health effects through inhalation and epidermal exposure. The risk of fungal exposure originates from the aerosolization of fungal spores. However, spore aerosolization is still not well understood. This paper provides a review of indoor fungal contamination, especially the aerosolization of fungal spores. We attempted to summarize what is known today and to identify what more information is needed to predict the aerosolization of fungal spores. This paper first reviews fungal contamination in indoor environments and HVAC systems. The detachment of fungal spores from colonies and the spore aerosolization principle are then summarized. Based on the above discussion, prediction methods for spore aerosolization are discussed. This review further clarifies the current situation and future efforts required to accurately predict spore aerosolization. This information is useful for forecasting and controlling the aerosolization of fungal spores.

Direct-Read Fluorescence-Based Measurements of Bioaerosol Exposure in Home Healthcare

Home healthcare workers (HHCWs) are subjected to variable working environments which increase their risk of being exposed to numerous occupational hazards. One of the potential occupational hazards within the industry includes exposure to bioaerosols. This study aimed to characterize concentrations of three types of bioaerosols utilizing a novel fluorescence-based direct-reading instrument during seven activities that HHCWs typically encounter in patients’ homes. Bioaerosols were measured in an indoor residence throughout all seasons in Cincinnati, OH, USA. A fluorescence-based direct-reading instrument (InstaScope, DetectionTek, Boulder, CO, USA) was utilized for all data collection. Total particle counts and concentrations for each particle type, including fluorescent and non-fluorescent particles, were utilized to form the response variable, a normalized concentration calculated as a ratio of concentration during activity to the background concentration. Walking experiments produced a median concentration ratio of 52.45 and 2.77 for pollen and fungi, respectively. Fungi and bacteria produced the highest and lowest median concentration ratios of 17.81 and 1.90 for showering, respectively. Lastly, our current study showed that sleeping activity did not increase bioaerosol concentrations. We further conclude that utilizing direct-reading methods may save time and effort in bioaerosol-exposure assessment.

Persistence of viable MS2 and Phi6 bacteriophages on carpet and dust

Resuspension of dust from flooring is a major source of human exposure to microbial contaminants, but the persistence of viruses on dust and carpet and the contribution to human exposure are often unknown. The goal of this work is to determine viability of MS2 and Phi6 bacteriophages on cut carpet, looped carpet, and house dust both over time and after cleaning. Bacteriophages were nebulized onto carpet or dust in artificial saliva. Viability was measured at 0, 1, 2, 3, 4, 24, and 48 h and after cleaning by vacuum, steam, hot water extraction, and disinfection. MS2 bacteriophages showed slower viability decay rates in dust (-0.11 hr^-1 ), cut carpet (-0.20 hr^-1 ), and looped carpet (-0.09 hr^-1 ) compared to Phi6 (-3.36 hr^-1 , -1.57 hr^-1 , and -0.20 hr^-1 , respectively). Viable viral concentrations were reduced to below the detection limit for steam and disinfection for both MS2 and Phi6 (p < 0.05), while vacuuming and hot water extraction showed no significant changes in concentration from uncleaned carpet (p > 0.05). These results demonstrate that MS2 and Phi6 bacteriophages can remain viable in carpet and dust for several hours to days, and cleaning with heat and disinfectants may be more effective than standard vacuuming.

Factors Influencing the Fungal Diversity on Audio-Visual Materials

The biodeterioration of audio–visual materials is a huge problem, as it can cause incalculable losses. To preserve these cultural heritage objects for future generations, it is necessary to determine the main agents of biodeterioration. This study focuses on identifying fungi, both from the air and smears from photographs and cinematographic films that differ in the type of carrier and binder, using high-throughput sequencing approaches. The alpha diversity measures of communities present on all types of carriers were compared, and a significant difference between cellulose acetate and baryta paper was observed. Next, the locality, type of carrier, and audio–visual material seem to affect the structure of fungal communities. Additionally, a link between the occurrence of the most abundant classes and species on audio–visual materials and air contamination in the archives was proven. In both cases, the most abundant classes were Agariomycetes, Dothideomycetes, and Eurotiomycetes, and approximately half of the 50 most abundant species detected on the audio–visual materials and in the air were identical.

Unraveling the Contact Network Patterns between Commercial Turkey Operation in North Carolina and the Distribution of Salmonella Species

Salmonellosis originating from poultry poses a significant threat to human health. Surveillance within production is thus needed to minimize risk. The objectives of this work were to investigate the distribution of Salmonella spp. from a commercial turkey operation and describe the animal movement patterns to investigate the association between contact network structure and Salmonella infection status. Four years of routine growout farm samples along with data on facility location, time since barns were built, production style, and bird movement data were utilized. From all of the surveillance samples collected, Salmonella serotyping was performed on positive samples and results showed that the most represented groups were C1 (28.67%), B (24.37%) and C2 (17.13%). The serovar Infantis (26.44%) was the most highly represented, followed by Senftenberg (12.76%) and Albany (10.93%). Results illustrated the seasonality of Salmonella presence with a higher number of positive samples being collected in the second half of each calendar year. We also demonstrated that Salmonella was more likely to occur in samples from older farms compared to farms built more recently. The contact network connectivity was low, although a few highly connected farms were identified. Results of the contact network showed that the farms which tested positive for Salmonella were not clustered within the network, suggesting that even though Salmonella dissemination occurs via transferring infected birds, for this study case it is unlikely the most important route of transmission. In conclusion, this study identified seasonality of Salmonella with significantly more cases in the second half of each year and also uncovered the role of between-farm movement of birds as not a major mode of Salmonella transmission.

Microbial growth and volatile organic compound (VOC) emissions from carpet and drywall under elevated relative humidity conditions

BACKGROUND

Microbes can grow in indoor environments if moisture is available, and we need an improved understanding of how this growth contributes to emissions of microbial volatile organic compounds (mVOCs). The goal of this study was to measure how moisture levels, building material type, collection site, and microbial species composition impact microbial growth and emissions of mVOCs. We subjected two common building materials, drywall, and carpet, to treatments with varying moisture availability and measured microbial communities and mVOC emissions.

RESULTS

Fungal growth occurred in samples at >75% equilibrium relative humidity (ERH) for carpet with dust and >85% ERH for inoculated painted drywall. In addition to incubated relative humidity level, dust sample collection site (adonis p=0.001) and material type (drywall, carpet, adonis p=0.001) drove fungal and bacterial species composition. Increased relative humidity was associated with decreased microbial species diversity in samples of carpet with dust (adonis p= 0.005). Abundant volatile organic compounds (VOCs) that accounted for >1% emissions were likely released from building materials and the dust itself. However, certain mVOCs were associated with microbial growth from carpet with dust such as C10H16H+ (monoterpenes) and C2H6SH+ (dimethyl sulfide and ethanethiol). CO2 production from samples of carpet with dust at 95% ERH averaged 5.92 mg hr-1 kg-1, while the average for carpet without dust at 95% ERH was 2.55 mg hr-1 kg-1.

CONCLUSION

Microbial growth and mVOC emissions occur at lower relative humidity in carpet and floor dust compared to drywall, which has important implications for human exposure. Even under elevated relative humidity conditions, the VOC emissions profile is dominated by non-microbial VOCs, although potential mVOCs may dominate odor production. Video Abstract.

Microbiological, Health and Comfort Aspects of Indoor Air Quality in a Romanian Historical Wooden Church

Monitoring the indoor microclimate in old buildings of cultural heritage and significance is a practice of great importance because of the importance of their identity for local communities and national consciousness. Most aged heritage buildings, especially those made of wood, develop an indoor microclimate conducive to the development of microorganisms. This study aims to analyze one wooden church dating back to the 1710s in Romania from the microclimatic perspective, i.e., temperature and relative humidity and the fungal load of the air and surfaces. One further aim was to determine if the internal microclimate of the monument is favorable for the health of parishioners and visitors, as well as for the integrity of the church itself. The research methodology involved monitoring of the microclimate for a period of nine weeks (November 2020–January 2021) and evaluating the fungal load in indoor air as well as on the surfaces. The results show a very high contamination of air and surfaces (>2000 CFU/m³). In terms of fungal contamination, Aspergillus spp. (two different species), Alternaria spp., Cladosporium spp., Mucor spp., Penicillium spp. (two different species) and Trichopyton spp. were the genera of fungi identified in the indoor wooden church air and Aspergillus spp., Cladosporium spp., Penicillium spp. (two different species) and Botrytis spp. on the surfaces (church walls and iconostasis). The results obtained reveal that the internal microclimate not only imposes a potential risk factor for the parishioners and visitors, but also for the preservation of the wooden church as a historical monument, which is facing a crisis of biodeterioration of its artwork.

Microbial analyses of blood spot surfaces collected from a laboratory and the bathroom of a female single-person household under different environmental conditions

Many people spend most of their time indoors, thereby exposing themselves to indoor environmental microbial communities that might interact with the human microbiota. These potential interactions have only been considered for personal identification; however, accumulating evidence indicates that these microbial interactions are potentially implicated with the identification of human interactions and location-specific factors including time and seasonal variations in the microbial community. To augment the potential of metagenomics-based forensic tools, we compared the composition of microbial communities in blood spot surfaces from healthy adults placed in different environments, such as in the bathroom of a female single-person household and on a laboratory, which were sampled across seasons and time points. The laboratory samples showed more changes in the bacterial community over time owing to the higher number of individuals using the laboratory, whereas the microbial communities in the bathroom samples remained relatively stable over time. Moreover, the two locations could be distinguished according to their specific bacterial community compositions. Variations were also observed related to changes in temperature and humidity, allowing for prediction of season-based microbial community. These findings offer a new perspective regarding the use of microbial community analysis in forensic science.

Practitioner-driven research for improving the outcomes of mold inspection and remediation

This commentary is intended to provide a research roadmap for utilizing recent chemical and molecular-biological technological advances for addressing dampness and mold in buildings. The perspective is unique in that both the mold industry practitioners and academic researchers drive the questions. Research needs were derived from a 2018 international workshop attended by practitioners, researchers and governmental representatives, where challenges and opportunities in the mold remediation and restoration field were discussed focusing on the need to develop new tools that improve building diagnosis and clearance certification for mold inspectors and remediators. Suggestions are made on how new technologies surrounding DNA-based sequence analysis for fungal and bacterial identification and real-time chemical sensor technology can be leveraged by practitioners to improve inspection and remediation. The workshop put into effect a logical progression to distill and extract practice-based implications and encourage the process of transfer of the science to practice. Goals for the workshop, and this subsequent paper, are also centered on encouraging US government-funding agencies to better position and define research on the built environment geared for end-user scientists and practitioners to better explore practical solutions to dampness and mold in indoor environments. By facilitating the workshop forum and targeting industry, field practitioners, and government agencies, a sharing of needed commonalities may be infused into future research agendas and outreach efforts.

Association between indoor microbiome exposure and sick building syndrome (SBS) in junior high schools of Johor Bahru, Malaysia

Sick building syndrome (SBS) is a collection of nonspecific syndromes linked with the built environment. The occurrence of SBS is associated with humidity, ventilation, moulds and microbial compounds exposure. However, no study has reported the association between indoor microbiome and SBS. In this study, 308 students were surveyed for SBS symptoms from 21 classrooms of 7 junior high schools from Johor Bahru, Malaysia, and vacuum dust from floor, desks and chairs was collected. High throughput amplicon sequencing (16S rRNA gene and ITS region) and quantitative PCR were conducted to characterize the absolute concentration of bacteria and fungi taxa. In total, 326 bacterial and 255 fungal genera were detected in dust with large compositional variation among classrooms. Also, half of these samples showed low compositional similarity to microbiome data deposited in the public database. The number of observed OTUs in Gammaproteobacteria was positively associated with SBS (p = 0.004). Eight microbial genera were associated with SBS (p < 0.01). Bacterial genera, Rhodomicrobium, Scytonema and Microcoleus, were protectively (negatively) associated with ocular and throat symptoms and tiredness, and Izhakiella and an unclassified genus from Euzebyaceae were positively associated with the throat and ocular symptoms. Three fungal genera, Polychaeton, Gympopus and an unclassified genus from Microbotryaceae, were mainly positively associated with tiredness. The associations differed with our previous study in microbial compounds (endotoxin and ergosterol) and SBS in the same population, in which nasal and dermal symptoms were affected. A higher indoor relative humidity and visible dampness or mould in classrooms were associated with a higher concentration of potential risk bacteria and a lower concentration of potential protective bacteria (p < 0.01). This is the first study to characterize the SBS-associated microorganisms in the indoor environment, revealing complex interactions between microbiome, SBS symptoms and environmental characteristics.

Profiling Airborne Microbiota in Mechanically Ventilated Buildings Across Seasons in Hong Kong Reveals Higher Metabolic Activity in Low-Abundance Bacteria

Metabolically active bacteria within built environments are poorly understood. This study aims to investigate the active airborne bacterial microbiota and compare the total and active microbiota in eight mechanically ventilated buildings over four consecutive seasons using the 16S rRNA gene (rDNA) and the 16S rRNA (rRNA), respectively. The relative abundances of the taxa of presumptive occupants and environmental origins were significantly different between the active and total microbiota. The Sloan neutral model suggested that ecological drift and random dispersal played a smaller role in the assembly of the active microbiota than the total microbiota. The seasonal nature of the active microbiota was consistent with that of the total microbiota in both indoor and outdoor environments, while only the indoor environment was significantly affected by geography. The relative abundances of the active and total taxa were positively correlated, suggesting that the high-abundance members were also the greatest contributors to the community-level metabolic activity. Based on the rRNA/rDNA ratio, the low-abundance members consistently had a higher taxon-level metabolic activity than the high-abundance members over seasons, suggesting that the low-abundance members may have the ability to survive and thrive in the indoor environment and their impact on the health of occupants cannot be overlooked.

DNA Sequence-Based Approach for Classifying the Mold Status of Buildings

Dampness or water damage in buildings and human exposure to the resultant mold growth is an ever-present public health concern. This study provides quantitative evidence that the airborne fungal ecology of homes with known mold growth ("moldy") differs from the normal airborne fungal ecology of homes with no history of dampness, water damage, or visible mold ("no mold"). Settled dust from indoor air and outdoor air and direct samples from building materials with mold growth were examined in homes from 11 cities across dry, temperate, and continental climate regions within the United States. Community analysis based on the sequence of the internal transcribed spacer region of fungal ribosomal RNA encoding genes demonstrated consistent and quantifiable differences between the fungal ecology of settled dust in homes with inspector-verified water damage and visible mold versus the settled dust of homes with no history of dampness, water damage, or visible mold. These differences include lower community richness (p_adj = 0.01) in the settled dust of moldy homes versus no mold homes, as well as distinct community taxonomic structures between moldy and no mold homes (ANOSIM, R = 0.15, p = 0.001). We identified 11 Ascomycota taxa that were more highly enriched in moldy homes and 14 taxa from Ascomycota, Basidiomycota, and Zygomycota that were more highly enriched in no mold homes. The indoor air differences between moldy versus no mold homes were significant for all three climate regions considered. These distinct but complex differences between settled dust samples from moldy and no homes were used to train a machine learning-based model to classify the mold status of a home. The model was able to accurately classify 100% of moldy homes and 90% of no mold homes. The integration of DNA-based fungal ecology with advanced computational approaches can be used to accurately classify the presence of mold growth in homes, assist with inspection and remediation decisions, and potentially lead to reduced exposure to hazardous microbes indoors.

Post-Flood Impacts on Occurrence and Distribution of Mycotoxin-Producing Aspergilli from the Sections Circumdati, Flavi, and Nigri in Indoor Environment

Mycotoxin-producing Aspergilli (Circumdati, Flavi, and Nigri), usually associated with contaminated food, may also cause respiratory disorders and are insufficiently studied in water-damaged indoor environments. Airborne (N = 71) and dust borne (N = 76) Aspergilli collected at post-flood and control locations in Croatia resulted in eleven different species based on their calmodulin marker: A. ochraceus, A. ostianus, A. pallidofulvus, A. sclerotiorum, and A. westerdijkiae (Circumdati); A. flavus (Flavi); and A. tubingensis, A. welwitschiae, A. niger, A. piperis, and A. uvarum (Nigri). Most of the airborne (73%) and dust borne (54%) isolates were found at post-flood locations, and the highest concentrations measured in indoor air (5720 colony-forming units (CFU)/m³) and dust (2.5 × 10⁵ CFU/g) were up to twenty times higher than in the control locations. A. flavus dominated among airborne isolates (25%) at the unrepaired locations, while 56% of the dust borne Aspergilli were identified as A. tubingensis and A. welwitschiae. The ability of identified isolates to produce mycotoxins aflatoxin B₁ (AFB₁), fumonisin B₂ (FB₂), and ochratoxin A were assessed by LC-MS analysis. All ochratoxin A (OTA)-producing Circumdati belonged to A. westerdijkiae (13.7 ± 15.81 µg/mL); in the section, FlaviA. flavus produced AFB₁ (2.51 ± 5.31 µg/mL), while A. welwitschiae and A. niger (section Nigri) produced FB₂ (6.76 ± 13.51 µg/mL and 11.24 ± 18.30 µg/mL, respectively). Water damage dominantly supported the occurrence of aflatoxigenic A. flavus in indoor environments. Yet unresolved, the causal relationship of exposure to indoor Aspergilli and adverse health effects may support the significance of this research.

Understanding building-occupant-microbiome interactions toward healthy built environments: A review

Built environments, occupants, and microbiomes constitute a system of ecosystems with extensive interactions that impact one another. Understanding the interactions between these systems is essential to develop strategies for effective management of the built environment and its inhabitants to enhance public health and well-being. Numerous studies have been conducted to characterize the microbiomes of the built environment. This review summarizes current progress in understanding the interactions between attributes of built environments and occupant behaviors that shape the structure and dynamics of indoor microbial communities. In addition, this review also discusses the challenges and future research needs in the field of microbiomes of the built environment that necessitate research beyond the basic characterization of microbiomes in order to gain an understanding of the causal mechanisms between the built environment, occupants, and microbiomes, which will provide a knowledge base for the development of transformative intervention strategies toward healthy built environments. The pressing need to control the transmission of SARS-CoV-2 in indoor environments highlights the urgency and significance of understanding the complex interactions between the built environment, occupants, and microbiomes, which is the focus of this review.

Modeling microbial growth in carpet dust exposed to diurnal variations in relative humidity using the "Time-of-Wetness" framework

Resuspension of microbes in floor dust and subsequent inhalation by human occupants is an important source of human microbial exposure. Microbes in carpet dust grow at elevated levels of relative humidity, but rates of this growth are not well established, especially under changing conditions. The goal of this study was to model fungal growth in carpet dust based on indoor diurnal variations in relative humidity utilizing the time-of-wetness framework. A chamber study was conducted on carpet and dust collected from 19 homes in Ohio, USA and exposed to varying moisture conditions of 50%, 85%, and 100% relative humidity. Fungal growth followed the two activation regime model, while bacterial growth could not be evaluated using the framework. Collection site was a stronger driver of species composition (P = 0.001, R2  = 0.461) than moisture conditions (P = 0.001, R2  = 0.021). Maximum moisture condition was associated with species composition within some individual sites (P = 0.001-0.02, R2  = 0.1-0.33). Aspergillus, Penicillium, and Wallemia were common fungal genera found among samples at elevated moisture conditions. These findings can inform future studies of associations between dampness/mold in homes and health outcomes and allow for prediction of microbial growth in the indoor environment.

Risk and impact of invasive fungal infections in patients with multiple myeloma

Infection is associated with great morbidity and mortality in patients with multiple myeloma (MM), but evidence for invasive fungal infections (IFIs) is lacking. We aimed to investigate risk factors for IFI in MM patients and to determine its impact on patients' survival. We retrospectively analyzed MM patients at Taipei Veterans General Hospital in Taiwan between January 2002 and October 2018. MM was diagnosed according to the International Myeloma Working Group criteria. IFI was defined according to the European Organization for Research and Treatment of Cancer/Mycoses Study Group criteria. All risk factors of IFI in MM patients were estimated using Cox regression models in the univariate and multivariate analyses. Of the 623 patients recruited, 22 (3.5%) were diagnosed with proven or probable IFI. Light chain disease (adjusted hazard ratio [HR] 6.74, 95% confidence interval [CI] 2.10-21.66), hemoglobin less than 8 g/dl (adjusted HR 3.34, 95% CI 1.32-8.42), serum albumin < 3.5 g/dl (adjusted HR 3.24, 95% CI 1.09-9.68), and having received allogeneic stem cell transplantation (allo-SCT) (adjusted HR 5.98, 95% CI 1.62-22.03) were significantly associated with IFI in the multivariate analysis. Contracting IFI was in turn associated with early mortality (adjusted HR 11.60, 95% CI 1.26-106.74). Light chain disease, anemia, hypoalbuminemia, and receiving allo-SCT were independent predictors of IFI in MM patients. The early mortality risk is much higher in those encountering IFI. Physicians must be aware of the rare but potentially lethal infections.

Sniffing fungi - phenotyping of volatile chemical diversity in Trichoderma species

Volatile organic compounds (VOCs) play vital roles in the interaction of fungi with plants and other organisms. A systematic study of the global fungal VOC profiles is still lacking, though it is a prerequisite for elucidating the mechanisms of VOC-mediated interactions. Here we present a versatile system enabling a high-throughput screening of fungal VOCs under controlled temperature. In a proof-of-principle experiment, we characterized the volatile metabolic fingerprints of four Trichoderma spp. over a 48 h growth period. The developed platform allows automated and fast detection of VOCs from up to 14 simultaneously growing fungal cultures in real time. The comprehensive analysis of fungal odors is achieved by employing proton transfer reaction-time of flight-MS and GC-MS. The data-mining strategy based on multivariate data analysis and machine learning allows the volatile metabolic fingerprints to be uncovered. Our data revealed dynamic, development-dependent and extremely species-specific VOC profiles from the biocontrol genus Trichoderma. The two mass spectrometric approaches were highly complementary to each other, together revealing a novel, dynamic view to the fungal VOC release. This analytical system could be used for VOC-based chemotyping of diverse small organisms, or more generally, for any in vivo and in vitro real-time headspace analysis.

Characteristics of airborne bacterial communities in indoor and outdoor environments during continuous haze events in Beijing: Implications for health care

There is solid evidence that haze pollution threatens human health owing to the abiotic pollutants it contains. However, the characteristics of airborne bacterial communities in indoor and outdoor environments exhibiting haze occurrence are still unknown. Thus, we examined variations in both indoor and outdoor airborne bacterial communities in Beijing from December 9-27, 2016, a period which included three haze events. The outdoor airborne bacterial communities were clustered into two main groups (Groups I and II), and they shifted between two typical bacterial communities regardless of the haze event. The Chao1, Shannon, and phylogenetic diversity indexes and abundance of dominant classes changed significantly, as did airborne bacterial community type. The indoor airborne bacterial community closely tracked the outdoor bacterial community type, forming two obvious groups supported by Adonis analysis, changes in dominant classes, and bacterial diversity compared to the outdoor group. Furthermore, we found that the airborne bacterial community type could affect the morbidity of respiratory diseases. Daily pneumonia cases were significantly higher in Group I (p = 0.035), whereas daily amygdalitis cases were significantly higher in Group II (p = 0.025). Interestingly, the enriched classes in the indoor environment were quite different from those in the typical airborne bacterial community environment, except for Clostridia, which had significantly higher abundance in both indoor environments. In conclusion, we found that the two indoor and outdoor airborne bacterial community types changed independently of haze events, and the special airborne bacterial community type was closely related to the incidence of pneumonia in the heavy haze season.

Microbial Community Composition Analysis in Spring Aerosols at Urban and Remote Sites over the Tibetan Plateau

This study presents features of airborne culturable bacteria and fungi from three different sites (Lanzhou; LZ; 1520 m ASL, Lhasa; LS; 3640 m ASL and Qomolangma; ZF; 4276 m ASL) representing urban (LZ and LS) and remote sites (ZF) over the Tibetan Plateau (TP). Total suspended particle (TSP) samples were collected with an air sampler (Laoying 2030, China) on a quartz filter. Community structures of bacteria and fungi were studied and compared among three different locations. The average levels of bacterial load in the outdoor air ranged from approximately 8.03 × 101 to 3.25 × 102 CFU m–3 (Colony forming unit per m3). However, the average levels of fungal loads ranged from approximately 3.88 × 100 to 1.55 × 101 CFU m−3. Bacterial load was one magnitude higher at urban sites LZ (2.06 × 102–3.25 × 102 CFU m−3) and LS (1.96 × 102–3.23 × 102 CFU m−3) compared to remote sites ZF (8.03 × 101–9.54 × 101 CFU m−3). Similarly, the maximum fungal load was observed in LZ (1.02 × 101–1.55 × 101 CFU m−3) followed by LS (1.03 × 101–1.49 × 101 CFU m−3) and ZF (3.88 × 100–6.26 × 100 CFU m−3). However, the maximum microbial concentration was observed on the same day of the month, corresponding to a high dust storm in Lanzhou during the sampling period. The reported isolates were identified by phylogenetic analysis of 16S rRNA genes for bacteria and ITS sequences for fungi amplified from directly extracted DNA. Bacterial isolates were mostly associated with Proteobacteria, Eurotiomycetes and Bacillus, whereas fungal isolates were mostly Aspergillus and Alternaria. Overall, this is a pioneer study that provides information about the airborne microbial concentration and composition of three sites over the TP region depending on environmental parameters. This study provided preliminary insight to carry out more advanced and targeted analyses of bioaerosol in the sites presented in the study.

Continental-Scale Microbiome Study Reveals Different Environmental Characteristics Determining Microbial Richness, Composition, and Quantity in Hotel Rooms

This is the first microbiome study to characterize the microbiome data and associated environmental characteristics in hotel environments. In this study, we found concordant variation between fungal compositional variation and absolute quantity and discordant variation between community variation/quantity and richness. Our study can be used to promote hotel hygiene standards and provide resource information for future microbiome and exposure studies associated with health effects in hotel rooms.

Culture-independent microbiome surveys have been conducted in homes, hospitals, schools, kindergartens and vehicles for public transport, revealing diverse microbial distributions in built environments. However, microbiome composition and the associated environmental characteristics have not been characterized in hotel environments. We presented here the first continental-scale microbiome study of hotel rooms (n = 68) spanning Asia and Europe. Bacterial and fungal communities were described by amplicon sequencing of the 16S rRNA gene and internal transcribed spacer (ITS) region and quantitative PCR. Similar numbers of bacterial (4,344) and fungal (4,555) operational taxonomic units were identified in the same sequencing depth, but most fungal taxa showed a restricted distribution compared to bacterial taxa. Aerobic, ubiquitous bacteria dominated the hotel microbiome with compositional similarity to previous samples from building and human nasopharynx environments. The abundance of Aspergillus was negatively correlated with latitude and accounted for ∼80% of the total fungal load in seven low-latitude hotels. We calculated the association between hotel microbiome and 16 indoor and outdoor environmental characteristics. Fungal composition and absolute quantity showed concordant associations with the same environmental characteristics, including latitude, quality of the interior, proximity to the sea, and visible mold, while fungal richness was negatively associated with heavy traffic (95% confidence interval [CI] = −127.05 to −0.25) and wall-to-wall carpet (95% CI = −47.60 to −3.82). Bacterial compositional variation was associated with latitude, quality of the interior, and floor type, while bacterial richness was negatively associated with recent redecoration (95% CI −179.00 to −44.55) and mechanical ventilation (95% CI = −136.71 to −5.12).

IMPORTANCE This is the first microbiome study to characterize the microbiome data and associated environmental characteristics in hotel environments. In this study, we found concordant variation between fungal compositional variation and absolute quantity and discordant variation between community variation/quantity and richness. Our study can be used to promote hotel hygiene standards and provide resource information for future microbiome and exposure studies associated with health effects in hotel rooms.

Indoor microbiome, environmental characteristics and asthma among junior high school students in Johor Bahru, Malaysia

Indoor microbial diversity and composition are suggested to affect the prevalence and severity of asthma by previous home microbiome studies, but no microbiome-health association study has been conducted in a school environment, especially in tropical countries. In this study, we collected floor dust and environmental characteristics from 21 classrooms, and health data related to asthma symptoms from 309 students, in junior high schools in Johor Bahru, Malaysia. The bacterial and fungal composition was characterized by sequencing 16s rRNA gene and internal transcribed spacer (ITS) region, and the absolute microbial concentration was quantified by qPCR. In total, 326 bacterial and 255 fungal genera were characterized. Five bacterial (Sphingobium, Rhodomicrobium, Shimwellia, Solirubrobacter, Pleurocapsa) and two fungal (Torulaspora and Leptosphaeriaceae) taxa were protective for asthma severity. Two bacterial taxa, Izhakiella and Robinsoniella, were positively associated with asthma severity. Several protective bacterial taxa including Rhodomicrobium, Shimwellia and Sphingobium have been reported as protective microbes in previous studies, whereas other taxa were first time reported. Environmental characteristics, such as age of building, size of textile curtain per room volume, occurrence of cockroaches, concentration of house dust mite allergens transferred from homes by the occupants, were involved in shaping the overall microbial community but not asthma-associated taxa; whereas visible dampness and mold, which did not change the overall microbial community for floor dust, was negatively associated with the concentration of protective bacteria Rhodomicrobium (β = -2.86, p = 0.021) of asthma. The result indicates complex interactions between microbes, environmental characteristics and asthma symptoms. Overall, this is the first indoor microbiome study to characterize the asthma-associated microbes and their environmental determinant in the tropical area, promoting the understanding of microbial exposure and respiratory health in this region.

Morphology and quantification of fungal growth in residential dust and carpets

Mold growth indoors is associated with negative human health effects, and this growth is limited by moisture availability. Dust deposited in carpet is an important source of human exposure due to potential elevated resuspension compared to hard floors. However, we need an improved understanding of fungal growth in dust and carpet to better estimate human exposure. The goal of this study was to compare fungal growth quantity and morphology in residential carpet under different environmental conditions, including equilibrium relative humidity (ERH) (50%, 85%, 90%, 95%, 100%), carpet fiber material (nylon, olefin, wool) and presence/absence of dust. We analyzed incubated carpet and dust samples from three Ohio homes for total fungal DNA, fungal allergen Alt a 1, and fungal morphology. Dust presence and elevated ERH (≥85%) were the most important variables that increased fungal growth. Elevated ERH increased mean fungal DNA concentration (P < 0.0001), for instance by approximately 1000 times at 100% compared to 50% ERH after two weeks. Microscopy also revealed more fungal growth at higher ERH. Fungal concentrations were up to 100 times higher in samples containing house dust compared to no dust. For fiber type, olefin had the least total fungal growth, and nylon had the most total fungi and A. alternata growth in unaltered dust. Increased ERH conditions were associated with increased Alt a 1 allergen concentration. The results of this study demonstrate that ERH, presence/absence of house dust, and carpet fiber type influence fungal growth and allergen production in residential carpet, which has implications for human exposure.