Size-resolved emission rates of airborne bacteria and fungi in an occupied classroom

Prediction of particle deposition around the cabin air supply nozzles of commercial airplanes using measured in-cabin particle emission rates

Enhanced soiling on the surfaces around air supply nozzles due to particle deposition is frequently observed in commercial airliners. The problem is worsened by severe outdoor air pollution and flight delays in China. The particles in an aircraft cabin originate from both outdoor and in-cabin sources. This study conducted measurements on multiple commercial flights to obtain particle emission rates from in-cabin sources. Additional experiments on a retired MD-82 airplane provided justification of the in-flight measurements. The in-cabin sources emitted more particles during boarding/deplaning than during meal servicing and sitting. The average PM2.5 emission rates were 7.2, 2.6, 1.9, and 1.8 (μg/min per person), respectively, during the boarding/deplaning, sitting on the ground, sitting in the air, and meal servicing. The corresponding PM10 emission rates were 15.4, 6.1, 5.3, and 5.4 (μg/min per person), respectively, for these four periods. The average particle emission rate from in-cabin sources varied seasonally and was the highest in winter. With the measured data, this investigation used a CFD model to predict the accumulation of particles deposited around the nozzles of an airplane, taking into account the flight routes and the outdoor particle concentrations at the airports where the airplanes were parked. For the most polluted airplane in China, the dirty spots/areas around the nozzles inside the airplane became visible after 6 months. The method proposed in this study can be used for any commercial airplane to predict the accumulation of particles deposited around the air supply nozzles.

Microfluidic System for Rapid Detection of Airborne Pathogenic Fungal Spores

Airborne fungi, including Aspergillus species, are the major causes of human asthma. Direct capture and analysis of pathogenic fungi in indoor air is important for disease prevention and control. In this paper, we demonstrated an integrated microfluidic system capable of enrichment and high-throughput detection for airborne fungal spores of Aspergillus niger, a well-known allergenic harmful species. The microfluidic system allowed semiquantitative detection of Aspergillus niger spores based on immunofluorescence analysis. To assess its contaminated level, the whole analysis time could be completed in 2-3 h including ∼1 h of enrichment and ∼1 h of target detection. The detection limit was ∼20 spores, equivalent to ∼300 spores·m^-3 of the concerned targets in air. In addition, the microfluidic system has integrated sampling and sample analysis to avoid additional sample concentration step, showing the potential for point-of-care detection for other pathogenic fungal spores.

Indoor Air Quality: A Bibliometric Study

What are the actual trends in Indoor Air Quality (IAQ), and in which direction is academic interest moving? Much progress has been made in identifying and mitigating indoor pollutants, due to both prevention campaigns (e.g., smoking bans) and greater control of product emissions. However, IAQ is still of interest and the future trends are unknown. In this study, a thorough bibliometric analysis was conducted on the scientific literature available on the Web of Science database with CiteSpace from 1990 until today. It was possible to identify past trends and current advances, both with the aim of introducing the IAQ topic to those encountering it for the first time and to examine the issues that are expected to be pertinent in the future.

Do surgeons and surgical facilities disturb the clean air distribution close to a surgical patient in an orthopedic operating room with laminar airflow?

BACKGROUND

Airflow distribution in the operating room plays an important role in ensuring a clean operating microenvironment and preventing surgical site infections (SSIs) caused by airborne contaminations. The objective of this study was to characterize the airflow distribution in proximity to a patient in an orthopedic operating room.

METHODS

Experimental measurements were conducted in a real operating room at St. Olav's Hospital, Norway, with a laminar airflow system. Omnidirectional anemometers were used to investigate the air distribution in the operating zone, and 4 different cases were examined with a real person and a thermal manikin.

RESULTS

This study showed that the downward airflow from the laminar airflow system varies in each case with different surgical arrangement, such as the position of the operating lamp. The results indicate that the interaction of thermal plumes from a patient and the downward laminar airflow may dominate the operating microenvironment.

CONCLUSIONS

The airflow distribution in proximity to a patient is influenced by both the surgical facility and the presence of medical staff. A thermal manikin may be an economical and practical way to study the interaction of thermal plumes and downward laminar airflow. The provision of higher clean airflow rate in the operating microenvironment may be an effective way to prevent the development of SSIs caused by indoor airborne contamination.

Longitudinal development of the dust microbiome in a newly opened Norwegian kindergarten

BACKGROUND

In Norway, 91% of children aged 1-5 attend kindergarten where they are exposed to indoor microbiomes which can have relevance for development and health. In order to gain a better understanding of the composition of the indoor microbiome and how it is affected by occupancy over time, floor dust samples from a newly opened kindergarten were investigated. Samples were collected during an 11-month period. Samples were analyzed for bacterial composition using 16S rRNA gene sequencing. Samples were also screened for four clinically relevant antibiotic resistance genes. In addition, Petrifilm analyses were used to evaluate surface hygiene.

RESULTS

Significant changes in the microbial community composition were observed over time (PERMANOVA, P < 0.05). Particularly, changes in the abundance and the proportions of human associated bacteria were found. A decrease in the prevalence of Propionibacterium from over 16% abundance to less than 1% and an increase in Streptococcus from 10 to 16% were the most significant findings. Four classes of clinically relevant antibiotic resistance genes were tested for; three were detected in the dust, indicating the presence of resistant bacteria and a potential for resistance spread. Petrifilm analysis showed that some surfaces in the kindergarten were of consistent poor hygienic quality, and new hygienic routines are required.

CONCLUSIONS

This study, which is the first of its kind performed at a newly opened kindergarten, reveals changes in the microbiome over time as well as the presence of antibiotic resistance genes and hygiene issues which are of relevance for occupant health.

Exploring temporal patterns of bacterial and fungal DNA accumulation on a ventilation system filter for a Singapore university library

Introduction

Ventilation system filters process recirculated indoor air along with outdoor air. This function inspires the idea of using the filter as an indoor bioaerosol sampler. While promising, there remains a need to investigate several factors that could limit the accuracy of such a sampling approach. Among the important factors are the dynamics of microbial assemblages on filter surfaces over time and the differential influence of outdoor versus recirculated indoor air.

Methods

This study collected ventilation system filter samples from an air handling unit on a regular schedule over a 21-week period and analyzed the accumulation patterns of biological particles on the filter both quantitatively (using fluorometry and qPCR) and in terms of microbial diversity (using 16S rDNA and ITS sequencing).

Results

The quantitative result showed that total and bacterial DNA accumulated monotonically, rising to 41 ng/cm² for total DNA and to 2.8 ng/cm² for bacterial DNA over the 21-week period. The accumulation rate of bacterial DNA correlated with indoor occupancy level. Fungal DNA first rose to 4.0 ng/cm² before showing a dip to 1.4 ng/cm² between weeks 6 and 10. The dip indicated a possible artifact of this sampling approach for quantitative analysis as DNA may not be conserved on the filter over the months-long service period. The sequencing results indicate major contributions from outdoor air for fungi and from recirculated indoor air for bacteria. Despite the quantitative changes, the community structure of the microbial assemblages was stable throughout the 21-week sampling period, highlighting the robustness of this sampling method for microbial profiling.

Conclusion

This study supports the use of ventilation system filters as indoor bioaerosol samplers, but with caveats: 1) an outdoor reference is required to properly understand the contribution of outdoor bioaerosols; and 2) there is a need to better understand the persistence and durability of the targeted organisms on ventilation system filters.

Fluorescent biological aerosol particles: Concentrations, emissions, and exposures in a northern California residence

Residences represent an important site for bioaerosol exposure. We studied bioaerosol concentrations, emissions, and exposures in a single-family residence in northern California with 2 occupants using real-time instrumentation during 2 monitoring campaigns (8 weeks during August-October 2016 and 5 weeks during January-March 2017). Time- and size-resolved fluorescent biological aerosol particles (FBAP) and total airborne particles were measured in real time in the kitchen using an ultraviolet aerodynamic particle sizer (UVAPS). Time-resolved occupancy status, household activity data, air-change rates, and spatial distribution of size-resolved particles were also determined throughout the house. Occupant activities strongly influenced indoor FBAP levels. Indoor FBAP concentrations were an order of magnitude higher when the house was occupied than when the house was vacant. Applying an integral material-balance approach, geometric mean of total FBAP emissions from human activities observed to perturb indoor levels were in the range of 10-50 million particles per event. During the summer and winter campaigns, occupants spent an average of 10 and 8.5 hours per day, respectively, awake and at home. During these hours, the geometric mean daily-averaged FBAP exposure concentration (1-10 μm diameter) was similar for each subject at 40 particles/L for summer and 29 particles/L for winter.

Building and environmental factors that influence bacterial and fungal loading on air conditioning cooling coils

We investigated bacterial and fungal concentrations on cooling coils of commercial AC units and quantified associations between microbial loads and AC unit or building operational parameters. A field campaign was conducted to sample 25 AC units in the humid, subtropical climate of Southern CT, USA and 15 AC units in the hot-summer Mediterranean climate of Sacramento, CA, USA. Median concentrations (with interquartile range) of bacteria and fungi on the cooling coils were 1.2 × 107 (5.1 × 106 -3.9 × 107 ) cells/m2 and 7.6 × 105 (5.6 × 104 -4.4 × 106 ) spore equivalents (SE)/m2 , respectively. Concentrations varied among units with median unit concentrations ranging three orders of magnitude for bacteria and seven orders of magnitude for fungi. Controlled comparisons and multivariable regressions indicate that dominant factors associated with AC coil loading include the nominal efficiency of upstream filters (P = .008 for bacteria and P < .001 for fungi) and coil moisture, which was reflected in fungal loading differences between top and bottom halves of the AC coils in Southern CT (P = .05) and the dew points of the two climates considered (P = .04). Environmental and building characteristics explained 42% (P < .001) of bacterial concentration variability and 66% (P < .001) of fungal concentration variability among samples.

Clothing as a transport vector for airborne particles: Chamber study

Strong evidence suggests that clothing serves as a reservoir of chemical pollutants and particles, including bioaerosols, which may have health significance. However, little is known about the role that clothing may play as a transport vector for inhaled airborne particles. Here, we contribute toward bridging the knowledge gap by conducting experiments to investigate clothing release fraction (CRF), determined as the size-dependent ratio of released to deposited particulate matter in the diameter range 0.5-10 μm. In a fully controlled chamber with low background particle levels, we deployed a programmable robot to reproducibly quantify the size-dependent CRF as a function of motion type and intensity, dust loadings, and activity duration. On average, 0.3%-3% of deposited particles were subsequently released with fabric motion, confirming that clothing can act as a vehicle for transporting airborne particles. The CRF increased with the vigor of movement and with dust loading. Rubbing and shaking the fabric were more effective than fabric stretching in resuspending particles. We also found that most of the release happened quickly after the onset of the resuspension activity. Particle size substantially influenced the CRF, with larger particles exhibiting higher values.

Pig Farmers' Homes Harbor More Diverse Airborne Bacterial Communities Than Pig Stables or Suburban Homes

Airborne bacterial communities are subject to conditions ill-suited to microbial activity and growth. In spite of this, air is an important transfer medium for bacteria, with the bacteria in indoor air having potentially major consequences for the health of a building’s occupants. A major example is the decreased diversity and altered composition of indoor airborne microbial communities as a proposed explanation for the increasing prevalence of asthma and allergies worldwide. Previous research has shown that living on a farm confers protection against development of asthma and allergies, with airborne bacteria suggested as playing a role in this protective effect. However, the composition of this beneficial microbial community has still not been identified. We sampled settled airborne dust using a passive dust sampler from Danish pig stables, associated farmers’ homes, and from suburban homes (267 samples in total) and carried out quantitative PCR measurements of bacterial abundance and MiSeq sequencing of the V3–V4 region of bacterial 16S rRNA genes found in these samples. Airborne bacteria had a greater diversity and were significantly more abundant in pig stables and farmers’ homes than suburban homes (Wilcoxon rank sum test P < 0.05). Moreover, bacterial taxa previously suggested to contribute to a protective effect had significantly higher relative and absolute abundance in pig stables and farmers’ homes than in suburban homes (ALDEx2 with P < 0.05), including Firmicutes, Peptostreptococcaceae, Prevotellaceae, Lachnospiraceae, Ruminococcaceae, Ruminiclostridium, and Lactobacillus. Pig stables had significantly lower airborne bacterial diversity than farmers’ homes, and there was no discernable direct transfer of airborne bacteria from stable to home. This study identifies differences in indoor airborne bacterial communities that may be an important component of this putative protective effect, while showing that pig stables themselves do not appear to directly contribute to the airborne bacterial communities in the homes of farmers. These findings improve our understanding of the role of airborne bacteria in the increasing prevalence of asthma and allergy.

Inactivation of filter bound aerosolized MS2 bacteriophages using a non-conductive ultrasound transducer

The inactivation of viruses that retain their infectivity when transmitted through the air is challenging. To address this issue, this study used a non-contact ultrasound transducer (NCUT) to generate shock waves in the air at specific distances, input voltages, and exposure durations, targeting bacteriophage virus aerosols captured on to H14 HEPA filters. Initially, a frequency of 27.56 kHz (50V) at 25-mm distance was used, which yielded an inactivation efficiency of up to 32.69 ± 12.10%. Other frequencies at shorter distances were investigated, where 29.10 kHz had the highest inactivation efficiency (up to 81.95 ± 9.79% at 8.5-mm distance and 100 V). Longer exposure times also influenced virus inactivation, but the results were inconclusive because the NCUT overheated with time. Overall, NCUT appears to be a promising method for inactivating virus aerosols that may be safer than other forms of inactivation, which can cause genetic mutations or produce dangerous by-products.

Urbanization Reduces Transfer of Diverse Environmental Microbiota Indoors

Expanding urbanization is a major factor behind rapidly declining biodiversity. It has been proposed that in urbanized societies, the rarity of contact with diverse environmental microbiota negatively impacts immune function and ultimately increases the risk for allergies and other immune-mediated disorders. Surprisingly, the basic assumption that urbanization reduces exposure to environmental microbiota and its transfer indoors has rarely been examined. We investigated if the land use type around Finnish homes affects the diversity, richness, and abundance of bacterial communities indoors. Debris deposited on standardized doormats was collected in 30 rural and 26 urban households in and near the city of Lahti, Finland, in August 2015. Debris was weighed, bacterial community composition determined by high throughput sequencing of bacterial 16S ribosomal RNA (rRNA) gene on the Illumina MiSeq platform, and the percentage of four different land use types (i.e., built area, forest, transitional, and open area) within 200 m and 2000 m radiuses from each household was characterized. The quantity of doormat debris was inversely correlated with coverage of built area. The diversity of total bacterial, Proteobacterial, Actinobacterial, Bacteroidetes, and Firmicutes communities decreased as the percentage of built area increased. Their richness followed the same pattern except for Firmicutes for which no association was observed. The relative abundance of Proteobacteria and particularly Gammaproteobacteria increased, whereas that of Actinobacteria decreased with increasing built area. Neither Phylum Firmicutes nor Bacteroidetes varied with coverage of built area. Additionally, the relative abundance of potentially pathogenic bacterial families and genera increased as the percentage of built area increased. Interestingly, having domestic animals (including pets) only altered the association between the richness of Gammaproteobacteria and diversity of Firmicutes with the built area coverage suggesting that animal ownership minimally affects transfer of environmental microbiota indoors from the living environment. These results support the hypothesis that people living in densely built areas are less exposed to diverse environmental microbiota than people living in more sparsely built areas.

Infant and Adult Inhalation Exposure to Resuspended Biological Particulate Matter

Human-induced resuspension of floor dust is a dynamic process that can serve as a major indoor source of biological particulate matter (bioPM). Inhalation exposure to the microbial and allergenic content of indoor dust is associated with adverse and protective health effects. This study evaluates infant and adult inhalation exposures and respiratory tract deposited dose rates of resuspended bioPM from carpets. Chamber experiments were conducted with a robotic crawling infant and an adult performing a walking sequence. Breathing zone (BZ) size distributions of resuspended fluorescent biological aerosol particles (FBAPs), a bioPM proxy, were monitored in real-time. FBAP exposures were highly transient during periods of locomotion. Both crawling and walking delivered a significant number of resuspended FBAPs to the BZ, with concentrations ranging from 0.5 to 2 cm^-3 (mass range: ∼50 to 600 μg/m³). Infants and adults are primarily exposed to a unimodal FBAP size distribution between 2 and 6 μm, with infants receiving greater exposures to super-10 μm FBAPs. In just 1 min of crawling or walking, 10³-10⁴ resuspended FBAPs can deposit in the respiratory tract, with an infant receiving much of their respiratory tract deposited dose in their lower airways. Per kg body mass, an infant will receive a nearly four times greater respiratory tract deposited dose of resuspended FBAPs compared to an adult.

Concentrations of Staphylococcus species in indoor air as associated with other bacteria, season, relative humidity, air change rate, and S. aureus-positive occupants

The aim of this study was to obtain knowledge about concentrations of Staphylococcus aureus, MRSA (methicillin-resistant S. aureus), and other Staphylococcus species in indoor air in Greater Copenhagen and about factors affecting the concentrations. The effects of season, temperature, relative humidity, air change rate (ACR), other bacterial genera, area per occupant, and presence of S. aureus-positive occupants were studied. In samples from 67 living rooms, S. hominis, S. warneri, S. epidermidis, and S. capitis were found in 13-25%; S. saprophyticus, S. cohnii, and S. pasteuri in 5-10%; and S. lugdunensis, S. haemolyticus, S. caprae, S. equorum, S. kloosii, S. pettenkoferi, S. simulans, and S. xylosus in less than 3%. Staphylococcus aureus were found in two of 67 living rooms: spa type t034 (an MRSA) was recovered from a farmhouse, while spa type t509 was found in an urban home. Two species, S. equorum and S. kloosii, were found only in the farmhouse. Staphylococcus was significantly associated with season with lowest concentration and richness in winter. Genera composition was associated with ACR with smaller fractions of Staphylococcus at higher ACR, while richness was significantly and negatively associated with area per occupant. Concentration of Staphylococcus correlated positively with the total concentration of bacteria, but negatively with the total concentration of other bacteria. The concentration of Staphylococcus was not significantly associated with concentrations of the other abundant genera Bacillus, Kocuria, and Micrococcus. In offices with S. aureus-positive occupants, airborne S. aureus was not found. In conclusion, Staphylococcus species constitute a considerable proportion of the airborne bacteria in the studied homes and offices. However, both S. aureus and MRSA had very low prevalence during all seasons. Thus, transmission of S. aureus and MRSA through the air in living rooms in Copenhagen is expected to be limited. The negative associations between ACR and the fraction Staphylococcus constituted out of total bacteria, and between area per occupant and Staphylococcus richness indicate that it might be possible to affect the presence of airborne Staphylococcus in homes.

Emission strength of airborne pathogens during toilet flushing

The flushing of toilets generates contaminated aerosols, the transmission of which may cause the spread of disease, particularly in the immunocompromised or the elderly. This study investigated the emission strength of three types of airborne bacteria, namely Staphylococcus epidermidis, Escherichia coli, and Pseudomonas alcaligenes, during toilet flushing in a custom-built toilet under a controlled environment. Flushing was activated by a flushometer operated at two pressure levels, 400 kPa (high pressure [HP]) and 200 kPa (low pressure [LP]), and by a water cistern tank placed 95 cm (high tank [HT]) and 46 cm (low tank [LT]) above the toilet seat. The pathogens emitted by the first flush were calculated, with the correlations between airborne pathogen emissions and droplet concentration (HP, r=0.944, P<.001; LP, r=0.803, P<.001, HT, r=0.885, P<.05) and bacterial size (HP, r=-0.919, P<.001; LP, r=-0.936, P<.001; HT, r=-0.967, P<.05) in the different conditions then tested. The emission strength in the HP condition was statistically greater than that in the LP condition, whereas the cistern tank system produced less emissions than the flushometer system, and tank height was not found to be a sensitive parameter.

Variability of indoor fungal microbiome of green and non-green low-income homes in Cincinnati, Ohio

"Green" housing is designed to use low-impact materials, increase energy efficiency and improve occupant health. However, little is known about the indoor mycobiome of green homes. The current study is a subset of a multicenter study that aims to investigate the indoor environment of green homes and the respiratory health of asthmatic children. In the current study, the mycobiome in air, bed dust and floor dust was compared between green (study site) and non-green (control site), low-income homes in Cincinnati, Ohio. The samples were collected at baseline (within four months following renovation), and 12months after the baseline at the study site. Parallel sample collection was conducted in non-green control homes. Air samples were collected by PM2.5 samplers over 5-days. Bed and floor dust samples were vacuumed after the air sampling was completed. The DNA sample extracts were analyzed using ITS amplicon sequencing. Analysis indicated that there was no clear trend in the fungal communities between green and non-green homes. Instead, fungal community differences were greatest between sample types - air, bed, and floor. Microbial communities also changed substantially between sampling intervals in both green and non-green homes for all sample types, potentially indicating that there was very little stability in the mycobiomes. Research gaps remain regarding how indoor mycobiome fluctuates over time. Longer follow-up periods might elucidate the effect of green renovation on microbial load in buildings.

Airborne bacterial assemblage in a zero carbon building: A case study

Currently, there is little information pertaining to the airborne bacterial communities of green buildings. In this case study, the air bacterial community of a zero carbon building (ZCB) in Hong Kong was characterized by targeting the bacterial 16S rRNA gene. Bacteria associated with the outdoor environment dominated the indoor airborne bacterial assemblage, with a modest contribution from bacteria associated with human skin. Differences in overall community diversity, membership, and composition associated with short (day-to-day) and long-term temporal properties were detected, which may have been driven by specific environmental genera and taxa. Furthermore, time-decay relationships in community membership (based on unweighted UniFrac distances) and composition (based on weighted UniFrac distances) differed depending on the season and sampling location. A Bayesian source-tracking approach further supported the importance of adjacent outdoor air bacterial assemblage in sourcing the ZCB indoor bioaerosol. Despite the unique building attributes, the ZCB microbial assemblage detected and its temporal characteristics were not dissimilar to that of conventional built environments investigated previously. Future controlled experiments and microbial assemblage investigations of other ZCBs will undoubtedly uncover additional knowledge related to how airborne bacteria in green buildings may be influenced by their distinctive architectural attributes.

Transmission of Airborne Bacteria across Built Environments and Its Measurement Standards: A Review

Human health is influenced by various factors including microorganisms present in built environments where people spend most of their lives (approximately 90%). It is therefore necessary to monitor and control indoor airborne microbes for occupational safety and public health. Most studies concerning airborne microorganisms have focused on fungi, with scant data available concerning bacteria. The present review considers papers published from 2010 to 2017 approximately and factors affecting properties of indoor airborne bacteria (communities and concentration) with respect to temporal perspective and to multiscale interaction viewpoint. From a temporal perspective, bacterial concentrations in built environments change depending on numbers of human occupancy, while properties of bacterial communities tend to remain stable. Similarly, the bacteria found in social and community spaces such as offices, classrooms and hospitals are mainly associated with human occupancy. Other major sources of indoor airborne bacteria are (i) outdoor environments, and (ii) the building materials themselves. Indoor bacterial communities and concentrations are varied with varying interferences by outdoor environment. Airborne bacteria from the outdoor environment enter an indoor space through open doors and windows, while indoor bacteria are simultaneously released to the outer environment. Outdoor bacterial communities and their concentrations are also affected by geographical factors such as types of land use and their spatial distribution. The bacteria found in built environments therefore originate from any of the natural and man-made surroundings around humans. Therefore, to better understand the factors influencing bacterial concentrations and communities in built environments, we should study all the environments that humans contact as a single ecosystem. In this review, we propose the establishment of a standard procedure for assessing properties of indoor airborne bacteria using four factors: temperature, relative humidity (RH), air exchange rate, and occupant density, as a minimum requirement. We also summarize the relevant legislation by country. Choice of factors to measure remain controversial are discussed.

Differences in bacterial composition between men's and women's restrooms and other common areas within a public building

Humans distribute a wide range of microorganisms around building interiors, and some of these are potentially pathogenic. Recent research established that humans are the main drivers of the indoor microbiome and up to now significant literature has been produced about this topic. Here we analyzed differences in bacterial composition between men's and women's restrooms and other common areas within the same public building. Bacterial DNA samples were collected from restrooms and halls of a three-floor building from the Federal University of Pampa, RS, Brazil. The bacterial community was characterized by amplification of the V4 region of the 16S rRNA gene and sequencing. Throughout all samples, the most abundant phylum was Proteobacteria, followed by Actinobacteria, Bacteroidetes and Firmicutes. Beta diversity metrics showed that the structure of the bacterial communities were different among the areas and floors tested, however, only 6-9% of the variation in bacterial communities was explained by the area and floors sampled. A few microorganisms showed significantly differential abundance between men's and women's restrooms, but in general, the bacterial communities from both places were very similar. Finally, significant differences among the microbial community profile from different floors were reported, suggesting that the type of use and occupant demographic within the building may directly influence bacterial dispersion and establishment.

DNA accumulation on ventilation system filters in university buildings in Singapore

Introduction

Biological particles deposit on air handling system filters as they process air. This study reports and interprets abundance and diversity information regarding biomass accumulation on ordinarily used filters acquired from several locations in a university environment.

Methods

DNA-based analysis was applied both to quantify (via DNA fluorometry and qPCR) and to characterize (via high-throughput sequencing) the microbial material on filters, which mainly processed recirculated indoor air. Results were interpreted in relation to building occupancy and ventilation system operational parameters.

Results

Based on accumulated biomass, average DNA concentrations per AHU filter surface area across nine indoor locations after twelve weeks of filter use were in the respective ranges 1.1 to 41 ng per cm² for total DNA, 0.02 to 3.3 ng per cm² for bacterial DNA and 0.2 to 2.0 ng DNA per cm² for fungal DNA. The most abundant genera detected on the AHU filter samples were Clostridium, Streptophyta, Bacillus, Acinetobacter and Ktedonobacter for bacteria and Aspergillus, Cladosporium, Nigrospora, Rigidoporus and Lentinus for fungi. Conditional indoor airborne DNA concentrations (median (range)) were estimated to be 13 (2.6–107) pg/m³ for total DNA, 0.4 (0.05–8.4) pg/m³ for bacterial DNA and 2.3 (1.0–5.1) pg/m³ for fungal DNA.

Conclusion

Conditional airborne concentrations and the relative abundances of selected groups of genera correlate well with occupancy level. Bacterial DNA was found to be more responsive than fungal DNA to differences in occupancy level and indoor environmental conditions.

Preparing for the crewed Mars journey: microbiota dynamics in the confined Mars500 habitat during simulated Mars flight and landing

BACKGROUND

The Mars500 project was conceived as the first full duration simulation of a crewed return flight to Mars. For 520 days, six crew members lived confined in a specifically designed spacecraft mock-up. The herein described "MIcrobial ecology of Confined Habitats and humAn health" (MICHA) experiment was implemented to acquire comprehensive microbiota data from this unique, confined manned habitat, to retrieve important information on the occurring microbiota dynamics, the microbial load and diversity in the air and on various surfaces. In total, 360 samples from 20 (9 air, 11 surface) locations were taken at 18 time-points and processed by extensive cultivation, PhyloChip and next generation sequencing (NGS) of 16S rRNA gene amplicons.

RESULTS

Cultivation assays revealed a Staphylococcus and Bacillus-dominated microbial community on various surfaces, with an average microbial load that did not exceed the allowed limits for ISS in-flight requirements indicating adequate maintenance of the facility. Areas with high human activity were identified as hotspots for microbial accumulation. Despite substantial fluctuation with respect to microbial diversity and abundance throughout the experiment, the location within the facility and the confinement duration were identified as factors significantly shaping the microbial diversity and composition, with the crew representing the main source for microbial dispersal. Opportunistic pathogens, stress-tolerant or potentially mobile element-bearing microorganisms were predicted to be prevalent throughout the confinement, while the overall microbial diversity dropped significantly over time.

CONCLUSIONS

Our findings clearly indicate that under confined conditions, the community structure remains a highly dynamic system which adapts to the prevailing habitat and micro-conditions. Since a sterile environment is not achievable, these dynamics need to be monitored to avoid spreading of highly resistant or potentially pathogenic microorganisms and a potentially harmful decrease of microbial diversity. If necessary, countermeasures are required, to maintain a healthy, diverse balance of beneficial, neutral and opportunistic pathogenic microorganisms. Our results serve as an important data collection for (i) future risk estimations of crewed space flight, (ii) an optimized design and planning of a spacecraft mission and (iii) for the selection of appropriate microbial monitoring approaches and potential countermeasures, to ensure a microbiologically safe space-flight environment.

City-scale distribution and dispersal routes of mycobiome in residences

BACKGROUND

Pathogenic and allergenic bacteria and fungi within the indoors can bring detrimental health effects on the occupants. We previously studied the bacterial communities found in households located throughout Hong Kong as well as the skin surfaces of the occupants. As a complementary study, here, we investigated the fungal communities (mycobiome) in the same residences and occupants and identified factors that are important in shaping their diversity, composition, distribution, and dispersal patterns.

RESULTS

We observed that common skin and environmental fungal taxa dominated air, surface, and skin samples. Individual and touch frequency strongly and respectively shaped the fungal community structure on occupant skin and residential surfaces. Cross-domain analysis revealed positive correlations between bacterial and fungal community diversity and composition, especially for skin samples. SourceTracker prediction suggested that some fungi can be transferred bidirectionally between surfaces and skin sites, but bacteria showed a stronger dispersal potential. In addition, we detected a modest but significant association between indoor airborne bacterial composition and geographic distance on a city-wide scale, a pattern not observed for fungi. However, the distance-decay effects were more pronounced at shorter local scale for both communities, and airflow might play a prominent role in driving the spatial variation of the indoor airborne mycobiome.

CONCLUSIONS

Our study suggests that occupants exert a weaker influence on surface fungal communities compared to bacterial communities, and local environmental factors, including air currents, appear to be stronger determinants of indoor airborne mycobiome than ventilation strategy, human occupancy, and room type.

Communicating the promise, risks, and ethics of large-scale, open space microbiome and metagenome research

The public commonly associates microorganisms with pathogens. This suspicion of microorganisms is understandable, as historically microorganisms have killed more humans than any other agent while remaining largely unknown until the late seventeenth century with the works of van Leeuwenhoek and Kircher. Despite our improved understanding regarding microorganisms, the general public are apt to think of diseases rather than of the majority of harmless or beneficial species that inhabit our bodies and the built and natural environment. As long as microbiome research was confined to labs, the public's exposure to microbiology was limited. The recent launch of global microbiome surveys, such as the Earth Microbiome Project and MetaSUB (Metagenomics and Metadesign of Subways and Urban Biomes) project, has raised ethical, financial, feasibility, and sustainability concerns as to the public's level of understanding and potential reaction to the findings, which, done improperly, risk negative implications for ongoing and future investigations, but done correctly, can facilitate a new vision of "smart cities." To facilitate improved future research, we describe here the major concerns that our discussions with ethics committees, community leaders, and government officials have raised, and we expound on how to address them. We further discuss ethical considerations of microbiome surveys and provide practical recommendations for public engagement.

Walker occupancy has an impact on changing airborne bacterial communities in an underground pedestrian space, as small-dust particles increased with raising both temperature and humidity

Although human occupancy is a source of airborne bacteria, the role of walkers on bacterial communities in built environments is poorly understood. Therefore, we visualized the impact of walker occupancy combined with other factors (temperature, humidity, atmospheric pressure, dust particles) on airborne bacterial features in the Sapporo underground pedestrian space in Sapporo, Japan. Air samples (n = 18; 4,800L/each sample) were collected at 8:00 h to 20:00 h on 3 days (regular sampling) and at early morning / late night (5:50 h to 7:50 h / 22:15 h to 24:45 h) on a day (baseline sampling), and the number of CFUs (colony forming units) OTUs (operational taxonomic units) and other factors were determined. The results revealed that temperature, humidity, and atmospheric pressure changed with weather. The number of walkers increased greatly in the morning and evening on each regular sampling day, although total walker numbers did not differ significantly among regular sampling days. A slight increase in small dust particles (0.3–0.5μm) was observed on the days with higher temperature regardless of regular or baseline sampling. At the period on regular sampling, CFU levels varied irregularly among days, and the OTUs of 22-phylum types were observed, with the majority being from Firmicutes or Proteobacteria (γ-), including Staphylococcus sp. derived from human individuals. The data obtained from regular samplings reveled that although no direct interaction of walker occupancy and airborne CFU and OTU features was observed upon Pearson's correlation analysis, cluster analysis indicated an obvious lineage consisting of walker occupancy, CFU numbers, OTU types, small dust particles, and seasonal factors (including temperature and humidity). Meanwhile, at the period on baseline sampling both walker and CFU numbers were similarly minimal. Taken together, the results revealed a positive correlation of walker occupancy with airborne bacteria that increased with increases in temperature and humidity in the presence of airborne small particles. Moreover, the results indicated that small dust particles at high temperature and humidity may be a crucial factor responsible for stabilizing the bacteria released from walkers in built environments. The findings presented herein advance our knowledge and understanding of the relationship between humans and bacterial communities in built environments, and will help improve public health in urban communities.

Monitoring biodiversity in libraries: a pilot study and perspectives for indoor air quality

Indoor Air Quality (IAQ) in libraries is influenced by the presence of specific factors which can impact on both paper storage as well as people health. Microclimatic conditions induce and support a biodiversity pattern involving environmental and anthropic microorganisms. We used a multidisciplinary monitoring model to characterize microflora biodiversity by Next Generation Sequencing (NGS). Biodiversity indexes were adapted to evaluate anthropic vs environmental pollution by combining Shannon mean index (H), species representativeness (E_H), human/environmental pollution ratio (SA) to better characterize the NGS output and acquire synthetic information on Indoor Air Microbial Biodiversity (IAMB). Results indicate a frequently low microbial load (IGCM/m³ < 1000) characterized by different species (n = 102), including several cellulose metabolizing bacteria. Workers and visitors appeared a relevant source of microbial contamination. Air biodiversity assayed by NGS seems a promising marker for studying IAQ.

Factors Shaping the Human Exposome in the Built Environment: Opportunities for Engineering Control

The "exposome" is a term describing the summation of one's lifetime exposure to microbes and chemicals. Such exposures are now recognized as major drivers of human health and disease. Because humans spend ∼90% of their time indoors, the built environment exposome merits particular attention. Herein we utilize an engineering perspective to advance understanding of the factors that shape the built environment exposome and its influence on human wellness and disease, while simultaneously informing development of a framework for intentionally controlling the exposome to protect public health. Historically, engineers have been focused on controlling chemical and physical contaminants and on eradicating microbes; however, there is a growing awareness of the role of "beneficial" microbes. Here we consider the potential to selectively control the materials and chemistry of the built environment to positively influence the microbial and chemical components of the indoor exposome. Finally, we discuss research gaps that must be addressed to enable intentional engineering design, including the need to define a "healthy" built environment exposome and how to control it.

Emission rates and the personal cloud effect associated with particle release from the perihuman environment

Inhalation exposure to elevated particulate matter levels is correlated with deleterious health and well-being outcomes. Despite growing evidence that identifies humans as sources of coarse airborne particles, the extent to which personal exposures are influenced by particle releases near occupants is unknown. In a controlled chamber, we monitored airborne total particle levels with high temporal and particle-size resolution for a range of simulated occupant activities. We also sampled directly from the subject's breathing zone to characterize exposures. A material-balance model showed that a sitting occupant released 8 million particles/h in the diameter range 1-10 μm. Elevated emissions were associated with increased intensity of upper body movements and with walking. Emissions were correlated with exposure, but not linearly. The personal PM₁₀ exposure increment above the room-average levels was 1.6-13 μg/m³ during sitting, owing to spatial heterogeneity of particulate matter concentrations, a feature that was absent during walking. The personal cloud was more discernible among larger particles, as would be expected for shedding from skin and clothing. Manipulating papers and clothing fabric was a strong source of airborne particles. An increase in personal exposure was observed owing to particle mass exchange associated with a second room occupant.

Influence of moisturizer and relative humidity on human emissions of fluorescent biological aerosol particles

Utilizing the ultraviolet light-induced fluorescence (UV-LIF) measurement technique as embodied in the Waveband Integrated Bioaerosol Sensor (WIBS-4A), we evaluated the fluorescent particle emissions associated with human shedding while walking in a chamber. The mean emission rates of supermicron (1-10 μm) fluorescent particles were in the range 6.8-7.5 million particles per person-h (~0.3 mg per person-h) across three participants, for conditions when the relative humidity was 60%-70% and no moisturizer was applied after showering. The fluorescent particles displayed a lognormal distribution with the geometric mean diameter in the range 2.5-4 μm and exhibited asymmetry factors that increased with particle size. Use of moisturizer was associated with changes in number and mass emission rates, size distribution, and particle shape. Emission rates were lower when the relative humidity was reduced, but these differences were not statistically significant.

Particulate matter from indoor environments of classroom induced higher cytotoxicity and leakiness in human microvascular endothelial cells in comparison with those collected from corridor

We investigated the physicochemical properties (size, shape, elemental composition, and endotoxin) of size resolved particulate matter (PM) collected from the indoor and corridor environments of classrooms. A comparative hazard profiling of these PM was conducted using human microvascular endothelial cells (HMVEC). Oxidative stress-dependent cytotoxicity responses were assessed using quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and high content screening (HCS), and disruption of monolayer cell integrity was assessed using fluorescence microscopy and transwell assay. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) analysis showed differences in the morphology and elemental composition of PM of different sizes and origins. While the total mass of PM collected from indoor environment was lower in comparison with those collected from the corridor, the endotoxin content was substantially higher in indoor PM (e.g., ninefold higher endotoxin level in indoor PM_8.1-20 ). The ability to induce oxidative stress-mediated cytotoxicity and leakiness in cell monolayer were higher for indoor PM compared to those collected from the corridor. In conclusion, this comparative analysis suggested that indoor PM is relatively more hazardous to the endothelial system possibly because of higher endotoxin content.

High temporal variability in airborne bacterial diversity and abundance inside single-family residences

Our homes are microbial habitats, and although the amounts and types of bacteria in indoor air have been shown to vary substantially across residences, temporal variability within homes has rarely been characterized. Here, we sought to quantify the temporal variability in the amounts and types of airborne bacteria in homes, and what factors drive this variability. We collected filter samples of indoor and outdoor air in 15 homes over 1 year (approximately eight time points per home, two per season), and we used culture-independent DNA sequencing approaches to characterize bacterial community composition. Significant differences in indoor air community composition were observed both between homes and within each home over time. Indoor and outdoor air community compositions were not significantly correlated, suggesting that indoor and outdoor air communities are decoupled. Indoor air communities from the same home were often just as different at adjacent time points as they were across larger temporal distances, and temporal variation correlated with changes in environmental conditions, including temperature and relative humidity. Although all homes had highly variable indoor air communities, homes with the most temporally variable communities had more stable, lower average microbial loads than homes with less variable communities.

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

Under sustained, elevated building moisture conditions, bacterial and fungal growth occurs. The goal of this study was to characterize microbial growth in floor dust at variable equilibrium relative humidity (ERH) levels. Floor dust from one home was embedded in coupons cut from a worn medium-pile nylon carpet and incubated at 50%, 80%, 85%, 90%, 95%, and 100% ERH levels. Quantitative PCR and DNA sequencing of ribosomal DNA for bacteria and fungi were used to quantify growth and community shifts. Over a 1-wk period, fungal growth occurred above 80% ERH. Growth rates at 85% and 100% ERH were 1.1 × 10⁴ and 1.5 × 10⁵ spore equivalents d^-1 mg dust^-1 , respectively. Bacterial growth occurred only at 100% ERH after 1 wk (9.0 × 10⁴ genomes d^-1 mg dust^-1 ). Growth resulted in significant changes in fungal (P<.00001) and bacterial community structure (P<.00001) at varying ERH levels. Comparisons between fungal taxa incubated at different ERH levels revealed more than 100 fungal and bacterial species that were attributable to elevated ERH. Resuspension modeling indicated that more than 50% of airborne microbes could originate from the resuspension of fungi grown at ERH levels of 85% and above.

Effects of human activities on concentrations of culturable bioaerosols in indoor air environments

We studied the effects of human activity on concentrations of fungal and bacterial bioaerosols in indoor air environments. We conducted measurement experiments for concentrations of bioaerosols and aerosol particles in test chambers with people performing various activities inside. We found that the number of people and human activities had positive correlations with the concentrations of bacterial bioaerosols. However, the concentration of fungal bioaerosols was not influenced by human presence or activities. The findings regarding the concentrations of fungal and bacterial bioaerosols and the effects of human presence and activities will be useful for studying control methods against bioaerosols.

Resilient microorganisms in dust samples of the International Space Station-survival of the adaptation specialists

BACKGROUND

The International Space Station (ISS) represents a unique biotope for the human crew but also for introduced microorganisms. Microbes experience selective pressures such as microgravity, desiccation, poor nutrient-availability due to cleaning, and an increased radiation level. We hypothesized that the microbial community inside the ISS is modified by adapting to these stresses. For this reason, we analyzed 8-12 years old dust samples from Russian ISS modules with major focus on the long-time surviving portion of the microbial community. We consequently assessed the cultivable microbiota of these samples in order to analyze their extremotolerant potential against desiccation, heat-shock, and clinically relevant antibiotics. In addition, we studied the bacterial and archaeal communities from the stored Russian dust samples via molecular methods (next-generation sequencing, NGS) and compared our new data with previously derived information from the US American ISS dust microbiome.

RESULTS

We cultivated and identified in total 85 bacterial, non-pathogenic isolates (17 different species) and 1 fungal isolate from the 8-12 year old dust samples collected in the Russian segment of the ISS. Most of these isolates exhibited robust resistance against heat-shock and clinically relevant antibiotics. Microbial 16S rRNA gene and archaeal 16S rRNA gene targeting Next Generation Sequencing showed signatures of human-associated microorganisms (Corynebacterium, Staphylococcus, Coprococcus etc.), but also specifically adapted extremotolerant microorganisms. Besides bacteria, the detection of archaeal signatures in higher abundance was striking.

CONCLUSIONS

Our findings reveal (i) the occurrence of living, hardy microorganisms in archived Russian ISS dust samples, (ii) a profound resistance capacity of ISS microorganisms against environmental stresses, and (iii) the presence of archaeal signatures on board. In addition, we found indications that the microbial community in the Russian segment dust samples was different to recently reported US American ISS microbiota.

Non-selective Separation of Bacterial Cells with Magnetic Nanoparticles Facilitated by Varying Surface Charge

Recovering microorganisms from environmental samples is a crucial primary step for understanding microbial communities using molecular ecological approaches. It is often challenging to harvest microorganisms both efficiently and unselectively, guaranteeing a similar microbial composition between original and separated biomasses. A magnetic nanoparticles (MNPs) based method was developed to effectively separate microbial biomass from glass fiber pulp entrapped bacteria. Buffering pH and nanoparticle silica encapsulation significantly affected both biomass recovery and microbial selectivity. Under optimized conditions (using citric acid coated Fe₃O₄, buffering pH = 2.2), the method was applied in the pretreatment of total suspended particle sampler collected bioaerosols, the effective volume for DNA extraction was increased 10-folds, and the overall method detection limit of microbial contaminants in bioaerosols significantly decreased. A consistent recovery of the majority of airborne bacterial populations was demonstrated by in-depth comparison of microbial composition using 16S rRNA gene high-throughput sequencing. Surface charge was shown as the deciding factor for the interaction between MNPs and microorganisms, which helps developing materials with high microbial selectivity. To our knowledge, this study is the first report using MNPs to separate diverse microbial community unselectively from a complex environmental matrix. The technique is convenient and sensitive, as well as feasible to apply in monitoring of microbial transport and other related fields.

Investigation of bacterial effects of Asian dust events through comparison with seasonal variability in outdoor airborne bacterial community

Atmospheric bacterial dispersion with aeolian dust has been reported to have a potential impact on public health and ecosystems. Asian dust is a major aeolian event that results in an estimated 4 million tons of Asian dust particles falling in Japan annually, 3,000–5,000 km away from their source regions. However, most studies have only investigated the effects of Asian dust during dust seasons. Therefore, in this study, outdoor bacterial abundance and community composition were determined by 16S rRNA quantitative PCR and amplicon sequencing, respectively, and compared on Asian and non-Asian dust days (2013–2015; 44 samples over four seasons). Seasonal variations in bacterial abundance of non-Asian dust days were not observed. Bacterial abundance of individual samples collected on non-Asian dust days changed dynamically relative to Asian dust days, with bacterial abundance occasionally reaching those of Asian dust days. The bacterial community composition on non-Asian dust days was rather stable seasonally, and did not differ from that on Asian dust days. These results indicate that bacteria in Asian dust does not immediately influence indigenous bacterial communities at the phylum/class level in distant downwind areas; accordingly, further studies of bacterial communities in downwind areas closer to the dust source are warranted.

Microorganisms in Confined Habitats: Microbial Monitoring and Control of Intensive Care Units, Operating Rooms, Cleanrooms and the International Space Station

Indoor environments, where people spend most of their time, are characterized by a specific microbial community, the indoor microbiome. Most indoor environments are connected to the natural environment by high ventilation, but some habitats are more confined: intensive care units, operating rooms, cleanrooms and the international space station (ISS) are extraordinary living and working areas for humans, with a limited exchange with the environment. The purposes for confinement are different: a patient has to be protected from infections (intensive care unit, operating room), product quality has to be assured (cleanrooms), or confinement is necessary due to extreme, health-threatening outer conditions, as on the ISS. The ISS represents the most secluded man-made habitat, constantly inhabited by humans since November 2000 – and, inevitably, also by microorganisms. All of these man-made confined habitats need to be microbiologically monitored and controlled, by e.g., microbial cleaning and disinfection. However, these measures apply constant selective pressures, which support microbes with resistance capacities against antibiotics or chemical and physical stresses and thus facilitate the rise of survival specialists and multi-resistant strains. In this article, we summarize the available data on the microbiome of aforementioned confined habitats. By comparing the different operating, maintenance and monitoring procedures as well as microbial communities therein, we emphasize the importance to properly understand the effects of confinement on the microbial diversity, the possible risks represented by some of these microorganisms and by the evolution of (antibiotic) resistances in such environments – and the need to reassess the current hygiene standards.

The Microbiome of the Built Environment and Human Behavior: Implications for Emotional Health and Well-Being in Postmodern Western Societies

It is increasingly evident that inflammation is an important determinant of cognitive function and emotional behaviors that are dysregulated in stress-related psychiatric disorders, such as anxiety and affective disorders. Inflammatory responses to physical or psychological stressors are dependent on immunoregulation, which is indicated by a balanced expansion of effector T-cell populations and regulatory T cells. This balance is in part driven by microbial signals. The hygiene or "old friends" hypothesis posits that exposure to immunoregulation-inducing microorganisms is reduced in modern urban societies, leading to an epidemic of inflammatory disease and increased vulnerability to stress-related psychiatric disorders. With the global trend toward urbanization, humans are progressively spending more time in built environments, thereby, experiencing limited exposures to these immunoregulatory "old friends." Here, we evaluate the implications of the global trend toward urbanization, and how this transition may affect human microbial exposures and human behavior.

The ecology of microscopic life in household dust

We spend the majority of our lives indoors; yet, we currently lack a comprehensive understanding of how the microbial communities found in homes vary across broad geographical regions and what factors are most important in shaping the types of microorganisms found inside homes. Here, we investigated the fungal and bacterial communities found in settled dust collected from inside and outside approximately 1200 homes located across the continental US, homes that represent a broad range of home designs and span many climatic zones. Indoor and outdoor dust samples harboured distinct microbial communities, but these differences were larger for bacteria than for fungi with most indoor fungi originating outside the home. Indoor fungal communities and the distribution of potential allergens varied predictably across climate and geographical regions; where you live determines what fungi live with you inside your home. By contrast, bacterial communities in indoor dust were more strongly influenced by the number and types of occupants living in the homes. In particular, the female : male ratio and whether a house had pets had a significant influence on the types of bacteria found inside our homes highlighting that who you live with determines what bacteria are found inside your home.

What Have We Learned about the Microbiomes of Indoor Environments?

The advent and application of high-throughput molecular techniques for analyzing microbial communities in the indoor environment have led to illuminating findings and are beginning to change the way we think about human health in relation to the built environment. Here I review recent studies on the microbiology of the built environment, organize their findings into 12 major thematic categories, and comment on how these studies have or have not advanced knowledge in each area beyond what we already knew from over 100 years of applying culture-based methods to building samples.

The advent and application of high-throughput molecular techniques for analyzing microbial communities in the indoor environment have led to illuminating findings and are beginning to change the way we think about human health in relation to the built environment. Here I review recent studies on the microbiology of the built environment, organize their findings into 12 major thematic categories, and comment on how these studies have or have not advanced knowledge in each area beyond what we already knew from over 100 years of applying culture-based methods to building samples. I propose that while we have added tremendous complexity to the rich existing knowledge base, the practical implications of this added complexity remain somewhat elusive. It remains to be seen how this new knowledge base will change how we design, build, and operate buildings. Much more research is needed to better understand the complexity with which indoor microbiomes may affect human health in both positive and negative ways.

What Have We Learned about the Microbiomes of Indoor Environments?

The advent and application of high-throughput molecular techniques for analyzing microbial communities in the indoor environment have led to illuminating findings and are beginning to change the way we think about human health in relation to the built environment. Here I review recent studies on the microbiology of the built environment, organize their findings into 12 major thematic categories, and comment on how these studies have or have not advanced knowledge in each area beyond what we already knew from over 100 years of applying culture-based methods to building samples. I propose that while we have added tremendous complexity to the rich existing knowledge base, the practical implications of this added complexity remain somewhat elusive. It remains to be seen how this new knowledge base will change how we design, build, and operate buildings. Much more research is needed to better understand the complexity with which indoor microbiomes may affect human health in both positive and negative ways.

Inflammatory potential in relation to the microbial content of settled dust samples collected from moisture-damaged and reference schools: results of HITEA study

Aiming to identify factors causing the adverse health effects associated with moisture-damaged indoor environments, we analyzed immunotoxicological potential of settled dust from moisture-damaged and reference schools in relation to their microbiological composition. Mouse RAW264.7 macrophages were exposed to settled dust samples (n = 25) collected from moisture-damaged and reference schools in Spain, the Netherlands, and Finland. After exposure, we analyzed production of inflammatory markers [nitric oxide (NO), tumor necrosis factor-α (TNF-)α, interleukin (IL)-6, and macrophage inflammatory protein (MIP)2] as well as mitochondrial activity, viability, apoptosis, and cell cycle arrest. Furthermore, particle counts, concentration of selected microbial groups as well as chemical markers such as ergosterol, 3-hydroxy fatty acids, muramic acid, endotoxins, and glucans were measured as markers of exposure. Dust from moisture-damaged schools in Spain and the Netherlands induced stronger immunotoxicological responses compared to samples from reference schools; the responses to Finnish samples were generally lower with no difference between the schools. In multivariate analysis, IL-6 and apoptosis responses were most strongly associated with moisture status of the school. The measured responses correlated with several microbial markers and numbers of particles, but the most important predictor of the immunotoxicological potential of settled dust was muramic acid concentration, a marker of Gram-positive bacteria.

The roles of the outdoors and occupants in contributing to a potential pan-microbiome of the built environment: a review

Recent high-throughput sequencing technology has led to an expansion of knowledge regarding the microbial communities (microbiome) across various built environments (BEs). The microbiome of the BE is dependent upon building factors and conditions that govern how outdoor microbes enter and persist in the BE. Additionally, occupants are crucial in shaping the microbiome of the BE by releasing human-associated microorganisms and resuspending microbes on floors and surfaces. Therefore, both the outdoors and occupants act as major sources of microorganisms found in the BE. However, most characterizations of the microbiome of the BE have been conducted in the Western world. Notably, outdoor locations and population groups present geographical variations in outdoor and human microbiomes, respectively. Given the influences of the outdoor and human microbiomes on BE microbiology, and the geographical variations in outdoor and human microbiomes, it is likely that the microbiomes of BEs also vary by location. The summation of microbiomes between BEs contribute to a potential BE pan-microbiome, which will both consist of microbes that are ubiquitous in indoor environments around the world, and microbes that appear to be endemic to particular geographical locations. Importantly, the BE pan-microbiome can potentially question the global application of our current views on indoor microbiology. In this review, we first provide an assessment on the roles of building and occupant properties on shaping the microbiome of the BE. This is then followed by a description of geographical variations in the microbiomes of the outdoors and humans, the two main sources of microbes in BEs. We present evidence of differences in microbiomes of BEs around the world, demonstrating the existence of a global pan-microbiome of the BE that is larger than the microbiome of any single indoor environment. Finally, we discuss the significance of understanding the BE pan-microbiome and identifying universal and location-specific relationships between building and occupant characteristics and indoor microbiology. This review highlights the much needed efforts towards determining the pan-microbiome of the BE, thereby identifying general and location-specific links between the microbial communities of the outdoors, human, and BE ecosystems, ultimately improving the health, comfort, and productivity of occupants around the world.

Toward a Predictive Understanding of Earth's Microbiomes to Address 21st Century Challenges

Microorganisms have shaped our planet and its inhabitants for over 3.5 billion years. Humankind has had a profound influence on the biosphere, manifested as global climate and land use changes, and extensive urbanization in response to a growing population. The challenges we face to supply food, energy, and clean water while maintaining and improving the health of our population and ecosystems are significant. Given the extensive influence of microorganisms across our biosphere, we propose that a coordinated, cross-disciplinary effort is required to understand, predict, and harness microbiome function. From the parallelization of gene function testing to precision manipulation of genes, communities, and model ecosystems and development of novel analytical and simulation approaches, we outline strategies to move microbiome research into an era of causality. These efforts will improve prediction of ecosystem response and enable the development of new, responsible, microbiome-based solutions to significant challenges of our time.