Insights into the Profile of the Human Expiratory Microbiota and Its Associations with Indoor Microbiotas

Insights into the effects of haze pollution on airborne bacterial communities and antibiotic resistance genes in fine particulate matter

Fine particulate matter (PM2.5) is a key component of haze pollution and poses a substantial threat to human health. However, airborne bacteria and antibiotic-resistance genes (ARGs), which are important biological components of PM2.5, have received less attention. In this study, we investigated the combined effects of haze on airborne bacteria and ARGs in PM2.5. Overall, during haze days, high concentrations of airborne bacteria (haze: 4782.24 ± 2689.85 cells/m3; non-haze: 2866.00 ± 1753.95 cells/m3) were observed with unique bacterial community structures. At the genus level, Microvirga, Arthrobacter, and JG30-KF-CM45 were identified as the bacterial biomarkers of haze days. Neutral processes contributed more to the establishment of airborne bacterial communities on haze days (R2 = 0.724) than that on non-hazy days (R2 = 0.338). The pathogenicity of bacterial communities per unit volume of air was significantly higher during haze days (169.36 ± 8.36 cell/m3) than that during non-haze days (112.66 ± 5.92 cell/m3) (p < 0.05). Redundancy analysis indicated that relatively stable atmospheric conditions and high concentrations of water-soluble ions (Na+, Mg2+, Ca2+, and F-), metals (Cd, As, Mn, and Cr), and carbonaceous fractions (elemental carbon) in PM2.5 play critical roles in shaping the bacterial community during haze days. On haze days, airborne ARGs exhibited unique distribution characteristics and network structures with dominant bacteria. This study highlighted the impact of haze days on airborne bacteria and ARGs on PM2.5 and provides a reference for managing the risks of bioaerosols.

Cockroach Microbiome Disrupts Indoor Environmental Microbial Ecology with Potential Public Health Implications

Cockroaches pose a significant global public health concern. However, besides the well-recognized cockroach-induced allergy, the potential impact of the cockroach microbiome on human health through various means is not yet fully elucidated. This study aimed to clarify the health impacts of cockroaches by investigating the microbial interactions among cockroaches, the indoor environment, and humans. We simultaneously collected cockroach, indoor environment (indoor air and floor dust), and human (exhaled breath condensate and skin) samples from residential areas in five cities representing distinct climate zones in China. The 16S rDNA sequencing results revealed that cockroaches harbor diverse bacterial populations that vary across different cities. The prevalence of potential pathogenic bacteria (PPB) in cockroaches ranged from 1.1% to 58.9%, with dominant resistance genes conferring resistance to tetracycline, macrolide, and beta-lactam. The relationships between the cockroach microbiome and the associated environmental and human microbiomes were explored by using fast expectation-maximization microbial source tracking (FEAST). The potential contribution of cockroach bacteria to the floor dust-borne microbiome and indoor airborne microbiome was estimated to be 5.6% and 1.3%, respectively. Similarly, the potential contribution of cockroach PPB to the floor dust-borne microbiome and indoor airborne microbiome was calculated to be 4.0% and 1.2%, respectively. In residences with cockroach infestations, the contribution of other sources to the indoor environment was slightly increased. Collectively, the role of cockroaches in the transmission of microorganisms, particularly pathogenic bacteria and antibiotic resistance genes, cannot be overlooked.

Variation and assembly mechanisms of Rhinolophus ferrumequinum skin and cave environmental fungal communities during hibernation periods

Animal skin acts as the barrier against invasion by pathogens and microbial colonizers. Environmental microbiota plays a significant role in shaping these microbial communities, which, in turn, have profound implications for host health. Previous research has focused on characterizing microorganisms on bats' skin and in their roosting environments, particularly bacterial communities. The emergence of white-nose syndrome, caused by the fungal-pathogen Pseudogymnoascus destructans, highlights the importance of understanding fungal dynamics in cave ecosystems and on bats' skin. In this study, we employed ITS amplicon sequencing to investigate the fungal community associated with the skin of Rhinolophus ferrumequinum and surfaces within hibernacula. In addition, we utilized neutral community and null models to assess the relative importance of stochastic and deterministic processes in fungal community assembly. The infection status of P. destructans did not significantly impact fungal community composition either on bat skin or cave environments. However, fungal diversity was significantly higher in cave environments compared to bat skin. Notably, potentially inhibitory genera of fungal pathogens were present in both bats and cave environments during hibernation. Furthermore, the composition and structure of fungal communities on both bat skin and cave environments varied across hibernation periods. Our findings suggest neutral processes primarily drive the assembly of fungal communities associated with hibernating R. ferrumequinum and cave environments, with dispersal limitation exerting a significant influence. This study provides insights into the fungal communities associated with hibernating R. ferrumequinum and cave environments.IMPORTANCEAnimal habitats provide sources and reservoirs for host microorganisms, making it critical to understand changes in microbial communities between habitats and hosts. While most studies have focused on bacterial microorganisms, research on fungal communities is lacking. This study investigated how community dynamics and assembly processes differ between the skin of hibernating Rhinolophus ferrumequinum and the cave environments under pathogen stress. We found significant differences in the composition and structure of the fungal communities between bat skin and roosting cave environments. Fungal genera with potential inhibitory effects on pathogens were found in all bat skin and cave environments. In addition, dispersal limitations during stochastic processes were a key factor in the formation of environmental fungal communities on bat skin and in caves. These findings offer new insights for exploring pathogen-host-environment-microbe interactions.

New Method of Direct Sampling Gas Chromatography-Ion Mobility Spectrometry to Identify the Dynamic Retronasal Volatile Compounds in the Alcoholic Beverage and Their Release Behaviors: A Case Study on Huangjiu

Owing to extremely low concentrations and dynamic changes, it is difficult to detect and trace the retronasal volatile organic compounds (VOCs) generated during the consumption of alcoholic beverages. We developed a direct sampling gas chromatography-ion mobility spectrometry (GC-IMS) method to identify the dynamic VOCs after drinking Huangjiu-a fermented alcoholic beverages. The optimal procedure was obtained: take a sip of 10 mL Huangjiu, holding it in mouth for 10 s and then swallow, and the VOCs in one nasal expiration were collected with gas sampling bag and transferred directly to the injection port of GC-IMS. The repeatability was satisfactory (RSD < 5%). Twenty-two VOCs were detected in Huangjiu, with esters and alcohols being dominant, which were divided into five distinct release behavior groups. Their release was found significantly inhibited by saliva. Overall, this new method offers a technical approach to understanding and assessing the characteristics of retronasal aroma in alcoholic beverages.

Impact of variations in airborne microbiota on pneumonia infection: An exploratory study

BACKGROUND

Previous studies showed airborne bacteria affect pneumonia incidence, but specific impacts of bacterial communities on Klebsiella pneumoniae infection were unknown.

METHODS

Five different ratios of bacterial community structures were randomly generated. Mice were divided into control, artificial bacterial community exposure, and corresponding Klebsiella pneumoniae challenge groups. Changes in body weight, blood parameters, pulmonary pathology, inflammatory factors, metabolomics, and fecal microbiota were analyzed.

RESULTS

Different bacterial community exposures had varying degrees of influence on body weight, complete blood count, inflammatory factors, alveolar lavage fluid and plasma metabolome, as well as intestinal microbiota at baseline and after infection. Metabolomic analysis showed that microbial exposure affected both bronchoalveolar lavage fluid and plasma metabolomes, suggesting systemic effects of microbial exposure on the organism. Differences in the structure of artificial microbiota had inconsistent effects on both the baseline state and the post-infection state, hinting at crosstalk between microbial exposure and Klebsiella pneumoniae infection. KEGG pathway analysis unveiled possible molecular mechanisms underlying the overall impact of microbial exposure on the lungs and the body as a whole. In the intestinal microbiota, differences were found in composition at the phylum and genus levels. Spearman correlation analysis established potential correlations between intestinal microbiota and differential metabolites, suggesting a potential link within the lung-gut axis.

CONCLUSION

This study demonstrated the significant and systemic impact of air microbiota structure differences on health. Future research should explore the underlying mechanisms to enhance our understanding of the air-environment-health relationship and identify interventions for improving public health strategies.

Biofilm Compositions and Bacterial Diversity on Kitchen Towels in Daily Use

Towels with complex woven structures are susceptible to biofilm formation during daily use. The composition of biofilms formed on towels used under real-life conditions has yet to be studied. Thus, we investigated the color changes, structural integrity, and biofilm development on towels used continuously for 10 weeks by 12 volunteers in specific kitchen environments. Apparent biofilms composed of bacteria and extracellular polymeric substances (EPSs) were found on all used towels. The bacteria concentrations ranged from 4 to 7 log CFU/g. Proteins were the most abundant EPS, followed by polysaccharides and eDNA. A high-throughput sequencing method was employed to investigate the bacterial diversity on the towels. The predominant bacterial genera differed from towel to towel. Kocuria, Rothia, Psychrobacter, Enhydrobacter, and Pseudomonas are genera of relatively high abundance that may originate from the human body and foods. In addition, correlations among environmental factors, major bacterial genera, physical properties, and biofilm formation of the towels were analyzed, which could provide a scientific reference for maintaining towel hygiene.

Traffic-related air pollution (TRAP) exposure, lung function, airway inflammation and expiratory microbiota: A randomized crossover study

Traffic-related air pollution (TRAP) has been linked with numerous respiratory diseases. Recently, lung microbiome is proposed to be characterized with development and progression of respiratory diseases. However, the underlying effects of TRAP exposure on lung microbiome are rarely explored. We conducted a randomized, crossover study among 35 healthy adults, who participated in 2-h exposure treatments in the road or park scenario alternately, to investigate the impact of short-term TRAP exposure on expiratory health. Particle matters (PMs), nitrogen dioxide (NO2), carbon monoxide (CO) and volatile organic compounds (VOCs), lung function, fractional exhaled nitric oxide (FeNO) and lung microbiota were measured. We applied linear mixed-effect models to explore the associations. TRAP including NO2 and CO in the road were about 1.5 times higher than that in the park except for PMs, and total VOCs also showed higher concentrations. We observed elevated difference in FeNO was associated with high TRAP exposure in the road session, but didn't find obvious changes in lung function. The abundance of Lentilactobacillus and Haepmophilus were distinct in the two groups, with significant correlations with changes to PEF and FeNO, respectively. Enrichment pathways related to transcription, amino acid and carbohydrate metabolism were altered following high TRAP exposure, suggesting TRAP contributed to the respiratory disease by changing metabolism of lung microbes. Our findings reveal VOCs in the road are another key air pollutant and provide novel mechanism for the respiratory effects of TRAP from the perspective of microbiome.

The dynamics and assembly patterns of airborne pathogen communities in the municipal food waste treatment system and its risk implications

While municipal solid waste (MSW) provides an ideal habitat for pathogen propagation, the dynamics and assembly of airborne pathogen communities in these environments remain largely unknown. Here, we combined amplicon and metagenomics with spatiotemporal sampling to study inhalable particulate matter-carried potential pathogenic bacteria at full-scale food waste treatment plants (FWTPs), alongside comparisons to urban air in the area. The results showed that pathogenic bacteria constituted a notable portion (64.5 % ± 20.6 %, n = 75) of the total bacterial communities in FWTPs-impacted air, with species and relative abundance 2-4 times higher than that of urban air, and contributed over 50 % of pathogens to the outdoor air. Airborne pathogen community structures were highly shaped by sampling sites (i.e. treatment units), but conserved across seasons (summer vs. winter) and particle sizes (PM2.5vs. PM10). Notably, Acinetobacter johnsonii-dominated pathogens (i.e. biofilm-related species) presented high levels of aerosolization and consistently occupied the upper-representative niches in all neutral models, highlighting their persistent exposure risk. Furthermore, pathogen community assembly was strongly driven by stochastic processes (58.8 %-96.8 %), while environmental variables explained only limited variations (3.4 %-28.7 %). In particular, the relative importance of stochastic processes clearly increased along an outdoor-to-indoor gradient (84.9 %-96.5 % vs. 71.3 %-76 %), which might be related to indoor anthropogenic activities that weaken microbial network stability and environmental filtering effects. This work enhances our knowledge of the dynamic behaviors and risk of airborne pathogen communities in MSW disposal and underscores the role of FWTPs in disseminating airborne pathogens.

Height-Resolved Analysis of Indoor Airborne Microbiome: Comparison with Floor Dust-Borne Microbiome and the Significance of Shoe Sole Dust

Exposure to the indoor airborne microbiome is closely related to the air that individuals breathe. However, the floor dust-borne microbiome is commonly used as a proxy for indoor airborne microbiome, and the spatial distribution of indoor airborne microbiome is less well understood. This study aimed to characterize indoor airborne microorganisms at varying heights and compare them with those in floor dust. An assembly of three horizontally and three vertically positioned Petri dishes coated with mineral oil was applied for passive air sampling continuously at three heights without interruption. The airborne microbiomes at the three different heights showed slight stratification and differed significantly from those found in the floor dust. Based on the apportionment results from the fast expectation-maximization algorithm (FEAST), shoe sole dust contributed approximately 4% to indoor airborne bacteria and 14% to airborne fungi, a contribution that is comparable to that from the floor dust-borne microbiome. The results indicated that floor dust may not be a reliable proxy for indoor airborne microbiome. Moreover, the study highlights the need for height-resolved studies of indoor airborne microbiomes among humans in different activity modes and life states. Additionally, shoe sole-dust-associated microorganisms could potentially be a source to "re-wild" the indoor microbiota.

Structure and assembly process of skin fungal communities among bat species in northern China

Background

The skin fungal communities of animals play a crucial role in maintaining host health and defending against pathogens. Because fungal infections can affect the skin microbiota of bats, gaining a comprehensive understanding of the characteristics of healthy bat skin fungal communities and the ecological processes driving them provides valuable insights into the interactions between pathogens and fungi.

Methods

We used Kruskal-Wallis tests and Permutational Multivariate Analysis of Variance (PERMANOVA) to clarify differences in skin fungal community structure among bat species. A Generalized Linear Model (GLM) based on a quasi-Poisson distribution and partial distance-based redundancy analysis (db-RDA) was performed to assess the influence of variables on skin fungal communities. Using community construction models to explore the ecological processes driving fungal community changes, t-tests and Wilcoxon tests were used to compare the alpha diversity and species abundance differences between the fungal structure on bat species' skin and the environmental fungal pool.

Results

We found significant differences in the composition and diversity of skin fungal communities among bat species influenced by temperature, sampling site, and body mass index. Trophic modes and skin fungal community complexity also varied among bat species. Null model and neutral model analysis demonstrated that deterministic processes dominated the assembly of skin fungal communities, with homogeneous selection as the predominant process. Skin fungal communities on bat species were impacted by the environmental fungal reservoir, and actively selected certain amplicon sequence variants (ASVs) from the environmental reservoir to adhere to the skin.

Conclusion

In this study, we revealed the structure and the ecological process driving the skin fungal community across bat species in northern China. Overall, these results broaden our knowledge of skin fungal communities among bat species, which may be beneficial to potential strategies for the protection of bats in China.

Indoor/Outdoor airborne microbiome characteristics in residential areas across four seasons and its indoor purification

Bioaerosols are more likely to accumulate in the residential environment, and long-term inhalation may lead to a variety of diseases and allergies. Here, we studied the distribution, influencing factors and diffusion characteristics of indoor and outdoor microbiota pollution in six residential buildings in Guangzhou, southern China over a period of one year. The results showed that the particle sizes of bioaerosol were mainly in the range of inhalable particle size (<4.7 μm) with a small difference among four seasons (74.61 % ± 2.17 %). The microbial communities showed obvious seasonal differences with high abundance in summer, but no obvious geographical differences. Among them, the bacteria were more abundant than the fungi. The dominant microbes in indoor and outdoor environments were similar, with Anoxybacillu, Brevibacillus and Acinetobacter as the dominant bacteria, and Cladosporium, Penicillium and Alternaria as the dominant fungi. The airborne microbiomes were more sensitive to temperature and particulate matter (PM2.5, PM10) concentrations. Based on the Sloan neutral model, bacteria were more prone to random diffusion than fungi, and the airborne microbiome can be randomly distributed in indoor and outdoor environments and between the two environments in each season. Bioaerosol in indoor was mainly from outdoor. The health risk evaluation showed that the indoor inhalation risks were higher than those outdoor. The air purifier had a better removal efficiency on 1.1-4.7 μm microorganisms, and the removal efficiency on Gram-negative bacteria was better than that on Gram-positive bacteria. This study is of great significance for the risk assessment and control of residential indoor bioaerosol exposure.

A case study showing highly traceable sources of bacteria on surfaces of university buildings

University students predominantly spend their time indoors, where prolonged exposure raises the risk of contact with microorganisms of concern. However, our knowledge about the microbial community characteristics on university campus and their underpinnings is limited. To address it, we characterized bacterial communities from the surfaces of various built environments typical of a university campus, including cafeterias, classrooms, dormitories, offices, meeting rooms, and restrooms, in addition to human skin. The classrooms harbored the highest α-diversity, while the cafeterias had the lowest α-diversity. The bacterial community composition varied significantly across different building types. Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, and Cyanobacteria were common phyla in university buildings, accounting for more than 90 % of total abundance. Staphylococcus aureus was the most abundant potential pathogen in classrooms, dormitories, offices, restrooms, and on human skin, indicating a potential risk for skin disease infections in these buildings. We further developed a new quantitative pathogenic risk assessment method according to the threat of pathogens to humans and found that classrooms exhibited the highest potential risk. The fast expectation-maximization algorithm identified 59 %-86 % of bacterial sources in buildings, with the human skin as the largest bacterial source for most buildings. As the sources of bacteria were highly traceable, we showed that homogeneous selection, dispersal limitation, and ecological drift were major ecological forces that drove community assembly. Our findings have important implications for predicting the distribution and sources of indoor dust bacterial communities on university campus.

Impact of climate zones and seasons on indoor airborne microbial communities: Insights from a comprehensive analysis

Bacteria and fungi are ubiquitous throughout built environments and are suspended in the air, potentially affecting human health. However, the impacts of climate zones on the diversity, structure, and stochastic assembly of indoor airborne microbes remain unknown. This study comprehensively analyzed indoor airborne microbes across five climate zones in China during the summer and winter using high-throughput sequencing. The diversity and structure of indoor airborne communities vary across climatic zones. A random forest model was used to identify biomarkers in different climate zones. The results showed no relationship between the biomarkers and their rankings in mean relative abundance. The Sloan neutral model fitting results indicated that the impact of climate zones on the stochastic process in the assembly of indoor airborne microbes was considerably more important than that of seasons. Additionally, the influence of seasons on the diversity, structure, and stochastic assembly process of indoor airborne microbes differed among different climate zones. The diversity, structure, and stochastic assembly processes of bacteria present distinctive outcomes in climate zones and seasons compared with those of fungi. Overall, these findings indicate that customized strategies are necessary to manage indoor airborne microbial communities in each climate zone, season, and for specific microbial species.

Unveiling the overlooked microbial niches thriving on building exteriors

Rapid urbanization in the Asia-Pacific region is expected to place two-thirds of its population in concrete-dominated urban landscapes by 2050. While diverse architectural facades define the unique appearance of these urban systems. There remains a significant gap in our understanding of the composition, assembly, and ecological potential of microbial communities on building exteriors. Here, we examined bacterial and protistan communities on building surfaces along an urbanization gradient (urban, suburban and rural regions), investigating their spatial patterns and the driving factors behind their presence. A total of 55 bacterial and protist phyla were identified. The bacterial community was predominantly composed of Proteobacteria (33.7% to 67.5%). The protistan community exhibited a prevalence of Opisthokonta and Archaeplastida (17.5% to 82.1% and 1.8% to 61.2%, respectively). The composition and functionality of bacterial communities exhibited spatial patterns correlated with urbanization. In urban buildings, factors such as facade type, light exposure, and building height had comparatively less impact on bacterial composition compared to suburban and rural areas. The highest bacterial diversity and lowest Weighted Average Community Identity (WACI) were observed on suburban buildings, followed by rural buildings. In contrast, protists did not show spatial distribution characteristics related to facade type, light exposure, building height and urbanization level. The distinct spatial patterns of protists were primarily shaped by community diffusion and the bottom-up regulation exerted by bacterial communities. Together, our findings suggest that building exteriors serve as attachment points for local microbial metacommunities, offering unique habitats where bacteria and protists exhibit independent adaptive strategies closely tied to the overall ecological potential of the community.

Contribution of Particulates to Airborne Disease Transmission and Severity: A Review

The emergence of coronavirus disease 2019 (COVID-19) has catalyzed great interest in the spread of airborne pathogens. Airborne infectious diseases are classified into viral, bacterial, and fungal infections. Environmental factors can elevate their transmission and lethality. Air pollution has been reported as the leading environmental cause of disease and premature death worldwide. Notably, ambient particulates of various components and sizes are harmful pollutants. There are two prominent health effects of particles in the atmosphere: (1) particulate matter (PM) penetrates the respiratory tract and adversely affects health, such as heart and respiratory diseases; and (2) bioaerosols of particles act as a medium for the spread of pathogens in the air. Particulates contribute to the occurrence of infectious diseases by increasing vulnerability to infection through inhalation and spreading disease through interactions with airborne pathogens. Here, we focus on the synergistic effects of airborne particulates on infectious disease. We outline the concepts and characteristics of bioaerosols, from their generation to transformation and circulation on Earth. Considering that microorganisms coexist with other particulates as bioaerosols, we investigate studies examining respiratory infections associated with airborne PM. Furthermore, we discuss four factors (meteorological, biological, physical, and chemical) that may impact the influence of PM on the survival of contagious pathogens in the atmosphere. Our review highlights the significant role of particulates in supporting the transmission of infectious aerosols and emphasizes the need for further research in this area.

Perspectives on Sampling and New Generation Sequencing Methods for Low-Biomass Bioaerosols in Atmospheric Environments

Bioaerosols play essential roles in the atmospheric environment and can affect human health. With a few exceptions (e.g., farm or rainforest environments), bioaerosol samples from wide-ranging environments typically have a low biomass, including bioaerosols from indoor environments (e.g., residential homes, offices, or hospitals), outdoor environments (e.g., urban or rural air). Some specialized environments (e.g., clean rooms, the Earth's upper atmosphere, or the international space station) have an ultra-low-biomass. This review discusses the primary sources of bioaerosols and influencing factors, the recent advances in air sampling techniques and the new generation sequencing (NGS) methods used for the characterization of low-biomass bioaerosol communities, and challenges in terms of the bias introduced by different air samplers when samples are subjected to NGS analysis with a focus on ultra-low biomass. High-volume filter-based or liquid-based air samplers compatible with NGS analysis are required to improve the bioaerosol detection limits for microorganisms. A thorough understanding of the performance and outcomes of bioaerosol sampling using NGS methods and a robust protocol for aerosol sample treatment for NGS analysis are needed. Advances in NGS techniques and bioinformatic tools will contribute toward the precise high-throughput identification of the taxonomic profiles of bioaerosol communities and the determination of their functional and ecological attributes in the atmospheric environment. In particular, long-read amplicon sequencing, viability PCR, and meta-transcriptomics are promising techniques for discriminating and detecting pathogenic microorganisms that may be active and infectious in bioaerosols and, therefore, pose a threat to human health.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41745-023-00380-x.

Characterization of airborne bacteria and fungi at a land-sea transition site in Southern China

Airborne microbe can have impact on regional to global climate as ice nuclei and cloud condensation nuclei. In coastal region, microbial aerosols are simultaneously contributed by terrestrial and marine sources under the influence of land-sea air exchange. We present a study on the characteristics of airborne bacteria and fungi, including their concentrations and communities, at a land-sea transition site in Southern China from December 2019 to December 2020. Seasonal variations of microbial communities were observed with evident profiles in summer, especially for fungal aerosols. The significant enhancement of Basidiomycota abundance in summer was contributed by local biogenic release under the influence of meteorological factors. Terrestrial sources are suggested as the dominant contributors to both bacterial and fungal aerosols rather than marine sources during the whole year period. Source-tracking analysis identified that marine contributions to airborne bacteria and fungi were 3.1-14.2 % and 4-24 %, respectively. It suggests that airborne fungi should be more suitable for long-range transport than airborne bacteria. This study improves the understanding of the conversional contribution of marine and terrestrial sources to airborne microbes in coastal region and the influencing environmental factors under land-sea exchange.

Skin microbiota interact with microbes on office surfaces

The indoor environment is recognized as a potential contributor to human health impacts through resident microbiomes. Indoor surface microbial communities are formed from several sources, environmental and anthropogenic. In this study, we characterized the bacterial and fungal communities from various sources typical of a working office environment including dust, fingers, and computer keyboards and mice. The composition of the dust bacterial community was significantly different from the other tested surfaces (P < 0.05), whereas the dust fungal community was only significantly different from fingers (P < 0.05). Bacterial and fungal communities were both shaped by deterministic processes, and bacterial communities had a higher migration rate. Results of a network analysis showed that the microbial community interactions of keyboards and mice were mainly competitive. Fast expectation-maximization microbial source tracking (FEAST) identified the sources of > 70 % of the keyboard and mouse microbial communities. Biomarkers for each sample types were identified by LDA Effect Size (LEfSE) analysis, some of which were soil-derived and potential anthropogenic pathogens, indicating the potential for exchange of microbes among outdoor, human and indoor surfaces. The current study shows that the source of microorganisms at the office interface is highly traceable and that their migration is linked to human activity. The migration of potentially pathogenic microbes were identified, emphasising the importance of personal hygiene.

Efficiency and sensitivity optimization of a protocol to quantify indoor airborne SARS-CoV-2 levels

Background

Development of methodologies to quantify airborne micro-organisms is needed for the prevention and control of infections. It is difficult to conclude which is the most efficient and sensitive strategy to assess airborne SARS-CoV-2 RNA levels due to the disparity of results reported in clinical settings.

Aim

To improve our previously reported protocol of measuring SARS-CoV-2 RNA levels, which was based on bioaerosol collection with a liquid impinger and RNA quantification with droplet digital polymerase chain reaction (ddPCR).

Methods

Air samples were collected in COVID-19 patient rooms to assess efficiency and/or sensitivity of different air samplers, liquid collection media, and reverse transcriptases (RT).

Findings

Mineral oil retains airborne RNA better than does hydrophilic media without impairing integrity. SARS-CoV-2 ORF1ab target was detected in 80% of the air samples using BioSampler with mineral oil. No significant differences in effectiveness were obtained with MD8 sampler equipped with gelatine membrane filters, but the SARS-CoV-2 copies/m³ air obtained with the latter were lower (28.4 ± 6.1 vs 9 ± 1.7). SuperScript II RT allows the detection of a single SARS-CoV-2 genome RNA molecule by ddPCR with high efficiency. This was the only RT that allowed the detection of SARS-CoV-2 N1 target in air samples.

Conclusion

The collection efficiency and detection sensivity of a protocol to quantify SARS-CoV-2 RNA levels in indoor air has been improved in the present study. Such optimization is important to improve our understanding of the microbiological safety of indoor air.

Bioaerosol Seasonal Variation and Contribution to Airborne Particulate Matter in Huangshi City of Central China

Ambient bioaerosols affect ecosystems and public health, but their seasonal variations and their contributions to aerosol particles are limitedly understood. Ambient bioaerosols in PM2.5 and PM10 samples were measured in Huangshi City, Hubei Province of China from April 2018 to December 2018. Bioaerosols were measured using a fluorescence microscope after staining with 4′, 6-diamino-2-phenylindole dihydrochloride (DAPI) following a direct staining technique. The bioaerosol number concentrations ranged from 0.12 to 15.69 # cm−3 for PM2.5 and 0.22 to 18.20 # cm−3 for PM10, with averages of 2.79 # cm−3 and 4.66 # cm−3, respectively. The bioaerosol concentrations of PM2.5 and PM10 varied significantly by seasons and were arranged in the following descending order: spring > fall > winter > summer. Bioaerosol numbers were dominated by fine particles of 0.37–2.5 μm diameter, while the spring bioaerosol particles were detected at the peak concentration of 0.56–1 μm diameter. Bioaerosol fractions accounted for 18.3 ± 10.6% PM10 mass and 13.7 ± 12.5% PM2.5 mass. Bioaerosol concentrations were increased during the haze event, but the increased amounts were not as large as those of the dust event, and higher bioaerosol contributions to PM were observed in the dust event than in the haze event. As enhanced emission controls have reduced PM concentrations in China, bioaerosols can be important contributors to PM mass.