Airborne Bacterial Communities Research Articles

Size resolved characteristics of urban and suburban bacterial bioaerosols in Japan as assessed by 16S rRNA amplicon sequencing

To study the size-resolved characteristics of airborne bacterial community composition, diversity, and abundance, outdoor aerosol samples were analysed by 16S rRNA gene-targeted quantitative PCR and amplicon sequencing with Illumina MiSeq. The samples were collected using size-resolved samplers between August and October 2016, at a suburban site in Toyama City and an urban site in Yokohama City, Japan. The bacterial communities were found to be dominated by Actinobacteria, Firmicutes, and Proteobacteria. At the genus level, we found a high abundance of human skin-associated bacteria, such as Propionibacterium, Staphylococcus, and Corynebacterium, in the urban site. Whereas, a high abundance of bacteria associated with soil and plants, such as Methylobacterium and Sphingomonas, was observed in the suburban site. Furthermore, our data revealed a shift in the bacterial community structure, diversity, and abundance of total bacteria at a threshold of 1.1-µm diameter. Interestingly, we observed that Legionella spp., the causal agents of legionellosis in humans, were mainly detected in > 2.1 µm coarse particles. Our data indicate that local environmental factors including built environments could influence the outdoor airborne bacterial community at each site. These results provide a basis for understanding the size-resolved properties of bacterial community composition, diversity, and abundance in outdoor aerosol samples and their potential influence on human health.

Dynamics of airborne bacterial community during biofiltration of gases from a swine house

Biofiltration is one of the important methods treating gases from swine houses. However, the dynamics of airborne bacterial community during biofiltration are unclear, which restricts the wide application of biofilters. In this research, the pine wood chips (W) and the mixture (pine wood chips + swine manure compost, WC) were selected as biofilter media, respectively, and the biofilters were operated to treat air exhausted from a nursing pig house. 16S rRNA gene sequencing was applied to analyze the airborne bacterial community before and after biofiltration. Results indicated that α-diversity of airborne bacteria had no significant change during biofiltration (P>0.05), and β-diversity analysis demonstrated that the bacterial community in gases after biofiltration was significantly different from that before biofiltration according to statistical analysis (P<0.001), while they were quite similar and more than 96% OTUs of them were the same. Therefore, it could be speculated that the airborne bacterial structure after biofiltration mainly depend on the inlet airborne bacterial community. In addition, the variations of airborne bacterial relative abundance and functions related to human diseases during biofiltration in two treatments were not all the same, which might imply that the dynamics of airborne bacterial structure during biofiltration were also affected by biofilter media. These results could help us to be aware of the variation of airborne bacterial community during biofiltration and the relevant influence factors, which may promote the improvement of biofiltration for gases from pig houses and reduce the pollution of bioaerosols.

Airborne bacteria confirm the pristine nature of the Southern Ocean boundary layer

Microorganisms are ubiquitous and highly diverse in the atmosphere. Despite the potential impacts of airborne bacteria found in the lower atmosphere over the Southern Ocean (SO) on the ecology of Antarctica and on marine cloud phase, no previous region-wide assessment of bioaerosols over the SO has been reported. We conducted bacterial profiling of boundary layer shipboard aerosol samples obtained during an Austral summer research voyage, spanning 42.8 to 66.5°S. Contrary to findings over global subtropical regions and the Northern Hemisphere, where transport of microorganisms from continents often controls airborne communities, the great majority of the bacteria detected in our samples were marine, based on taxonomy, back trajectories, and source tracking analysis. Further, the beta diversity of airborne bacterial communities varied with latitude and temperature, but not with other meteorological variables. Limited meridional airborne transport restricts southward community dispersal, isolating Antarctica and inhibiting microorganism and nutrient deposition from lower latitudes to these same regions. A consequence and implication for this region's marine boundary layer and the clouds that overtop it is that it is truly pristine, free from continental and anthropogenic influences, with the ocean as the dominant source controlling low-level concentrations of cloud condensation nuclei and ice nucleating particles.

Air Microbiome and Pollution: Composition and Potential Effects on Human Health, Including SARS Coronavirus Infection.

Polluted air poses a significant threat to human health. Exposure to particulate matter (PM) and harmful gases contributes to cardiovascular and respiratory diseases, including allergies and obstructive lung disease. Air pollution may also be linked to cancer and reduced life expectancy. Uptake of PM has been shown to cause pathological changes in the intestinal microbiota in mice and humans. Less is known about the effects of pollution-associated microbiota on human health. Several recent studies described the microbiomes of urban and rural air samples, of the stratosphere and sand particles, which can be transported over long distances, as well as the air of indoor environments. Here, we summarize the current knowledge on airborne bacterial, viral, and fungal communities and discuss their potential consequences on human health. The current data suggest that bacterial pathogens are typically too sparse and short-lived in air to pose a significant risk for infecting healthy people. However, airborne fungal spores may exacerbate allergies and asthma. Little information is available on viruses including phages, and future studies are likely to detect known and novel viruses with a yet unknown impact on human health. Furthermore, varying experimental protocols have been employed in the recent microbiome and virome studies. Therefore, standardized methodologies will be required to allow for better comparisons between studies. Air pollution has been linked to more severe outcomes of SARS (severe acute respiratory syndrome) coronavirus (SARS-CoV) infections. This may have contributed to severe SARS-CoV-2 outbreaks, especially those in China, Northern Italy, Iran, and New York City.

Variation in Near-Surface Airborne Bacterial Communities among Five Forest Types

Airborne bacteria play important roles in air pollution, human health and biogeochemical cycles. However, their spatial variation and determinant factors in forest environments are poorly understood. In this study, we selected five forest types in the Liuxihe National Park, South China, to analyze how near-surface bacterial community structure is related to the forest community structure and soil physicochemical properties. The results indicated that the dominant communities were mainly constituted by seven bacterial genera of the phyla Proteobacteria (49.7%–55.4%) and Firmicutes (44.2%–49.8%), including Exiguobacterium (42.0%–46.4%), Citrobacter (20.7%–25.8%), Acinetobacter (20.1%–22.1%), and Pseudomonas (7.8%–8.9%) etc. However, differences in the composition and diversity of the airborne bacterial communities were evident among the five forests, especially with respect to the dominant taxa. The relative abundance of Enterococcus and Bacillus in coniferous and broad-leaved mixed forest (MF), broad-leaved mixed forest (BF), and pure Cunninghamia lanceolata forest (CL) was significantly higher than that of the other forests, while the relative abundance of Citrobacter was significantly lower. The relative abundance of Citrobacter, Acinetobacter, and Pseudomonas in Proteobacteria were significantly negatively correlated with plant diversity and acid phosphatase activity but positively correlated with soil pH and soil available potassium. Contrastingly, the correlation between the relative abundance of most genera of Firmicutes and the above environmental factors is just the opposite of that for Proteobacteria. We provide direct evidence that native plant communities in the middle stage of succession, compared to planted forests and forest open space, generally had higher airborne bacterial diversity. Airborne bacterial diversity showed a significantly positive correlation with plant diversity (p &lt; 0.05). Over all, soil pH, soil available potassium, and soil available phosphorus contributed to a high rate of the diversity of the airborne bacterial community in near-surface, followed by the plant diversity of the arbor layer and the near-surface air temperature. These results extended our understanding of the ecological patterns of airborne bacteria in forest ecosystems.

The major chemical constituents of PM2.5 and airborne bacterial community phyla in Beijing, Seoul, and Nagasaki

Ambient particle (PM2.5) samples were collected in three East Asian cities (Beijing, China; Seoul, South Korea; Nagasaki, Japan) from December 2014 to November 2015 to quantitatively investigate airborne bacteria at the phylum level. Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Cyanobacteria represented the top five airborne bacterial phyla in all three cities. The most dominant airborne phylum, Proteobacteria, was more prevalent during the winter (at rates of 67.2%, 79.9%, and 87.0% for Beijing, Seoul, and Nagasaki, respectively). Correlations among airborne bacteria and environmental factors including PM2.5, its major chemical constituents, and meteorological factors were calculated. Temperature correlated negatively with Proteobacteria but positively with Firmicutes and Bacteroidetes. The abundance of Cyanobacteria correlated positively with particulate NO3− and SO42− levels in Beijing (R = 0.46 and R = 0.35 for NO3− and SO42−, respectively) but negatively in Seoul (R = −0.14 and R = −0.19 for NO3− and SO42−, respectively) and Nagasaki (R = −0.05 and R = −0.03 for NO3− and SO42−, respectively). Backward trajectory analysis was applied for 72 h and three clusters were classified in each city. Five dominant bacteria and other bacterial groups showed significant differences (p < 0.05) in local clustering, as compared to the long-range transport clusters from Beijing. The proportions of the five bacterial phyla in Seoul were significantly different in each cluster. A local cluster in Nagasaki had higher ratios of all major airborne bacterial phyla, except Proteobacteria.

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

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

Effects of aerosol pollution on PM2.5-associated bacteria in typical inland and coastal cities of northern China during the winter heating season

Frequent heavy aerosol pollution occurs during the winter heating season in northern China. Here, we characterized the airborne bacterial community structure and concentration, during typical pollution episodes that occurred during the winter heating season of 2017–2018 in Jinan and Weihai. During this heating season, five and four heavy pollution episodes were observed in Jinan and Weihai, respectively. Compared with December and January, pollution episodes in March were significantly affected by sand dust events. Higher Bacillales were identified in the March samples from Jinan, indicating that sand dust influences bacterial communities. During similar pollution episodes, air pollution in the coastal city of Weihai was lower than the inland city of Jinan. The predominant bacteria included Staphylococcus, Cyanobacteria, Lactobacillus, Deinococcus, Enbydrobacter, Ralstonia, Bacillus, Comamonas, and Sphingomonas. These predominant bacteria are mainly from Proteobacteria, Firmicutes, Cyanobacteria, Actinobacteria, and Bacteroidetes phyla. Bacterial concentration showed significant variation with increased airborne pollutants. The highest concentration appeared during moderate pollution (up to 106 cells/m3), whereas bacterial concentration decreased during heavy and severe pollution (105 cells/m3), which may be related to toxic effects of high pollutant concentrations during heavy or severe pollution. Community structure variation indicated that Cyanobacterial genera were dominant in clean or slight pollution. With increased PM2.5, Staphylococcus increased and became the most abundant bacteria in moderate pollution (up to 40%). During heavy or severe pollution, bacteria that are adaptable to harsh or extreme environments predominate, such as Deinococcus and Bacillus. In the assessment of health risks from air pollution, the bioaerosols risks must consider. Additionally, although most microbial genera are similar between the two cities, there are important differences associated with pollution level. During air pollution regulation in different regions with varied geographical and climatic conditions, bioaerosol pollution difference is an unignored factor.

Seasonal shift in airborne microbial communities.

Microorganisms are ubiquitous in the atmosphere. Global investigations on the geographical and temporal distribution of airborne microbial communities are critical for identifying the sources and the factors shaping airborne communities. At mid-latitude sites, a seasonal shift in both the concentration and diversity of airborne microbial communities has been systematically observed in the planetary boundary layer. While the factors suspected of affecting this seasonal change were hypothesized (e.g., changes in the surface conditions, meteorological parameters and global air circulation), our understanding on how these factors influence the temporal variation of airborne microbial communities, especially at the microbial taxon level, remains limited. Here, we investigated the distribution of both airborne bacterial and fungal communities on a weekly basis over more than one year at the mid-latitude and continental site of puy de Dôme (France; +1465m altitude above sea level). The seasonal shift in microbial community structure was likely correlated to the seasonal changes in the characteristics of puy de Dôme's landscape (croplands and natural vegetation). The airborne microbial taxa that were the most affected by seasonal changes trended differently throughout the seasons in relation with their trophic mode. In addition, the windy and variable local meteorological conditions found at puy de Dôme were likely responsible for the intraseasonal variability observed in the composition of airborne microbial communities.

Airborne bacterial communities and antibiotic resistance gene dynamics in PM2.5 during rainfall

The biotoxicity and public health effects of airborne bacteria and antibiotic resistance genes (ARGs) in fine particulate matter (PM2.5) are being increasingly recognized. The characteristics of bacterial community composition and ARGs in PM2.5 under different rainfall conditions were studied based on the on-site synchronous measurements in downtown Beijing. Marked differences were evident in the bacterial community characteristics of PM2.5 before, during, and after rain events (p < 0.05). The rain intensities affected the bacterial community abundance in PM2.5 and heavy rain had greater washing effects. The Proteobacteria (phylum level), α-Proteobacteria (class level), Pseudomonadales (order level), Pseudomonadaceae (family level), and Cyanobacteria (genus level) were the dominant bacterial taxa associated with PM2.5 in Beijing during rain events. However, the bacteria at each level that displayed the biggest percentage variance was not the dominant type under different rain intensities. The ermB, tetW, and mphE genes were the primary ARGs, with abundances of 18 to 30 copies/m3, which was a relatively smaller value than other observations. Real-time monitoring of the meteorological condition of rain events and physicochemical properties of PM2.5 were used to identify the main factors during rainfall. The bacterial community was sensitive to the ionic and metal element components of PM2.5 during rainfall. The abundance of ARGs was closely correlated with some groups of the bacterial community, which were also close to the initial value before the rain. Statistical analysis demonstrated that temperature, relative humidity, and duration of rain were the primary meteorological factors for the biological characteristics. The ionic species, rather than metal elements, in PM2.5 were the sensitive factors for the bacteria community and ARGs, which varied at the phylum, class, order, family, and genus levels. The observations provide insights for the biological risk assessment in an urban rainfall water and the potential health impact on citizens.

Structural Characteristics and Functional Implications of PM2.5 Bacterial Communities During Fall in Beijing and Shanghai, China.

Air pollution characterized by fine particulate matter (PM2.5) frequently has occurred in China, and has posed threats to human health. The physiochemical characteristics of airborne PM2.5 have been extensively studied, but its bacterial structures and functions have not yet been well studied. Herein, we focused on the structural characteristics and functional implications of airborne bacteria under different pollution levels in Beijing and Shanghai. The α- and β-diversities showed no obvious difference in two cities (p > 0.05). The dominant phyla Proteobacteria, Firmicutes, and Actinobacteria with total abundance of over 92% were found in all PM2.5 samples. The results of weighted unifrac non-metric multidimensional scaling (NMDS) suggested that air pollution was no obviously correlated with bacterial community but dispersed disorderly. Furthermore, canonical correlation analysis (CCA) and permutation test indicated that , , and wind speed were the key factors that associated with airborne bacterial community structure. Chemical components of particulate matter played more important role in structuring bacterial community than meteorological conditions based on the result of partial CCA. In addition, the annotation of metabolic pathway suggested that the predominant genus Pseudomonas was obviously correlated with disease infections. Several dominant species might contribute to organic degradation, nitrogen cycles, and ice-nuclei activities in environments. Overall, this work enhanced our understanding of functions of airborne bacteria and highlighted their potential role in atmospheric chemical progresses.

Source identification of airborne bacteria in the mountainous area and the urban areas

Abstract Airborne microbes are an abundant component of the atmospheric aerosol, which has important influences on atmospheric conditions and public health. However, their possible sources have not been well-studied. To identify the sources of airborne bacteria, airborne PM2.5, PM10 samples and microorganism samples from surface-soil and leaves were collected at three different sampling sites involved in the mountainous area and urban areas in Xi'an, China in summer and autumn. The samples were then analyzed by fluorescence staining and high-throughput sequencing to explore the relationship in bacterial community structures between ambient air samples and possible sources. Results show that the concentrations of airborne microbes differed among sites and between seasons. The airborne bacterial community structures also varied with seasons and sites, with seasonal differences being greater than spatial ones. In both seasons, leaf-surface represented the main local source of airborne bacteria. At the mountainous area, bacteria from surface-soil and leaf-surface contributed the most to the airborne microbial community; at both mountainous and urban areas, this contribution was more pronounced in autumn. Furthermore, back trajectories arriving at the three sampling sites showed that the airborne bacteria may come from other regions by long-distance airflow. The results of this study provide a better understanding about the sources of ambient bacteria.

Microbial composition in seasonal time series of free tropospheric air and precipitation reveals community separation

Primary biological aerosols are transported over large distances, are traveling in various media such as dry air masses, clouds or fog, and eventually deposited with dry deposition, especially for larger particles, or precipitation like rain, hail or snow. To investigate relative abundance and diversity of airborne bacterial and fungal communities, samples have been collected with a liquid impinger (Coriolis µ) from the top of Mount Sonnblick (3106 m asl, Austrian Alps) from the respective sources under a temporal aspect over four seasons over the year to include all climatic conditions. Bacterial and fungal samples (16S rRNA and ITS) were sequenced using Illumina MiSeq paired-end sequencing, investigated for relative abundance by qPCR(16S rRNA and 18S rRNA) and ice nucleation activity. Results show that there is no stable free tropospheric air microbial community and air mass origin was different for the four sampling periods which exerted influence on the microbial composition of the atmosphere although a core microbiome could be identified consisting of 61 bacterial OTUs and eight fungal genera. Differentiation between seasons was stronger pronounced in air than in precipitation, with rain being most different and variable of precipitation types, indicating distinct forces driving microbial fate in the air. Microorganisms precipitated with snow, hail or rain or being transported by clouds differ in their species composition from free tropospheric air masses and do not mirror the air community structure. They were more diverse, distinct in composition, 16S:18S ratio and abundance from free-floating PBA. Hence, snow or cloud samples are not suitable proxies for free tropospheric air microbiome composition, since separation processes in aerosolization, transport and scavenging occur. The microbial composition of arriving precipitation or clouds represents only a part of the microbial air composition communities of the cumulative sources of origin. Relative abundance and composition of ice nucleation-active bacteria showed a higher share of relative % reads of known ice nucleation-active bacteria present in all wet phases compared to air. Results propose a separation of IN-active reads with higher shares occurring in precipitation. This study presents the first comparison of free tropospheric bacterial and fungal abundance and diversity in time series of air over several seasons in contrast to various precipitation forms in the free troposphere.

Airborne bacteria in the Central Mediterranean: Structure and role of meteorology and air mass transport

The 16S rRNA gene metabarcoding approach has been used to characterize the structure of the airborne bacterial community of PM10 samples, and investigate the dependence on meteorology, seasons, and long-range transported air masses. The PM10 samples were collected at a Central Mediterranean coastal site, away from large sources of local pollution. Proteobacteria, Cyanobacteria, Actinobacteria, Firmicutes, and Bacteroidetes, which were found in all samples, were the most abundant phyla. Calothrix, Pseudomonas, and Bacillus were the most abundant genera. The within-sample relative abundance (RA) of each phylum/genus varied from sample to sample. Calothrix was the most abundant genus during the advection of desert dust and Atlantic air masses, Pseudomonas was the most abundant genus when the advected air flows spent several hours over lands or close to lands affected by anthropogenic activities, before reaching the study site.The bacterial community richness and biodiversity of the PM10 samples on average increased from winter to spring, while the sample dissimilarity on average decreased from winter to spring. The spring meteorological conditions over the Mediterranean, which have likely contributed to maintain for longer time the bacterial community in the atmosphere, could have been responsible for the above results.The analysis of the presumptive species-level characterization of the airborne bacterial community has revealed that the abundance of human (opportunistic) pathogens was highly inhomogeneous among samples, without any significant change from winter to spring. We also found that the PM10 samples collected during the advection of desert dust and Atlantic air masses were on average the less enriched in human (opportunistic) pathogenic species.

Bacterial communities in PM2.5 and PM10 in broiler houses at different broiler growth stages in spring.

The welfare and healthy growth of poultry under intensive feeding conditions are closely related to their living environment. In spring, the air quality considerably decreases due to reduced ventilation and aeration in cage systems, which influences the meat quality and health of broilers during normal growth stages. In this study, we analyzed the airborne bacterial communities in PM2.5 and PM10 in cage broiler houses at different broiler growth stages under intensive rearing conditions based on the high-throughput 16S rDNA sequencing technique. Our results revealed that PM2.5, PM10 and airborne microbes gradually increased during the broiler growth cycle in poultry houses. Some potential or opportunistic pathogens, including Acinetobacter, Pseudomonas, Enterococcus, Microbacterium, etc., were found in the broiler houses at different growth stages. Our study evaluated variations in the microbial communities in PM2.5 and PM10 and potential opportunistic pathogens during the growth cycle of broilers in poultry houses in the spring. Our findings may provide a basis for developing technologies for air quality control in caged poultry houses.

Vertical distributions of airborne microorganisms over Asian dust source region of Taklimakan and Gobi Desert

Airborne microorganisms transported by dust events from Asian Deserts influence climate changes, ecosystem dynamics and human health in the westerly-wind blowing areas of East Asia. However, the vertical transport of airborne microorganisms was not understood in detail. We collected aerosols at high altitudes (800 m and 500 m) and ground levels (5 m and 10 m) at Asian dust-source area, such as the Taklimakan and Gobi Deserts, for analyzing compositions and abundances of the airborne microorganisms that are distributed vertically over desert area. Assessment of the dust particles using an optical particle counter and microscopic observation counts demonstrated that the mineral and microbial particles remained suspended at altitudes of over 300 m and decreased to half to one-tenth of concentrations compared to those at the ground level. High-throughput sequencing of 16S rRNA genes (bacterial taxonomic marker) revealed that the airborne bacterial communities were mixed vertically at the altitudes of some hundreds of meters over both the sites and were predominantly composed of the phyla Actinobacteria, Firmicutes, Bacteroidetes, and Proteobacteria. In contrast, using sequencing analysis of internally transcribed spacer regions (fungal taxonomic markers), the fungal community structures over both the sites were different at high altitudes and ground levels. Sequences belonging to the phylum Ascomycota increased at high altitudes and comprised those of a commonly detected mold that includes the genera Cladosporium and Alternaria and is thought to be resistant to atmospheric stressors. Our results indicate that airborne bacterial communities are easily mixed vertically over dust-source desert, while stressor-tolerant fungi of airborne Ascomycota remain at high altitudes of desert atmosphere.

Seasonal Changes of Airborne Bacterial Communities Over Tokyo and Influence of Local Meteorology.

In order to study airborne bacterial community dynamics over Tokyo, including fine-scale correlations between airborne microorganisms and meteorological conditions, and the influence of local versus long-range transport of microbes, air samples were collected on filters for periods ranging from 48 to 72 h. The diversity of the microbial community was assessed by next generation sequencing. Predicted source regions of airborne particles, from back trajectory analyses, changed abruptly from the Pacific Ocean to the Eurasian Continent in the beginning of October. However, the microbial community composition and the alpha and beta diversities were not affected by this shift in meteorological regime, suggesting that long-range transport from oceanic or continental sources was not the principal determinant controlling the local airborne microbiome. By contrast, we found a significant correlation between the local meteorology, especially relative humidity and wind speed, and both alpha diversity and beta diversity. Among four potential local source categories (soil, bay seawater, river, and pond), bay seawater and soil were identified as constant and predominant sources. Statistical analyses point toward humidity as the most influential meteorological factor, most likely because it is correlated with soil moisture and hence negatively correlated with the dispersal of particles from the land surface. In this study, we have demonstrated the benefits of fine-scale temporal analyses for understanding the sources and relationships with the meteorology of Tokyo’s “aerobiome.”

Assessment of Airborne Bacterial and Fungal Communities in Selected Areas of Teaching Hospital, Kandy, Sri Lanka

Nosocomial infections, in lay term known as hospital acquired infections, are caused mainly by airborne pathogens found in healthcare facilities and their surroundings. The aim of this study was to quantify and identify bacteria and fungi in a hospital, which is an understudied area of air quality in Sri Lanka. Air samples were collected in agar medium and petri plates containing sterile filter papers. The number of culturable and total airborne microorganisms was estimated by manual counting and fluorescent microscopy, respectively. The morphologically distant bacteria and fungi were identified by DNA sequencing. The statistical analysis revealed significant variances between studied sites (p < 0.05) where Outpatients Department and Respiratory Unit showed higher levels of airborne microbial load. Culturable microbial count was higher at noon (hospital visiting hours) compared to other sampling periods (after hospital visiting hours) within the hospital. Total count of airborne microbes was found to be the highest during the afternoon. The most sensitive zones such as Operating Theatre and Intensive Care Unit showed considerably higher counts of airborne microbes. Identification by molecular means revealed the presence of human pathogens in the hospital air including Bacillus sp, Micrococcus sp, Pseudomonas sp, Staphylococcu ssp, Exiguobacterium sp, Enterobacter sp, Escherichia sp, Sphingomonas sp, Massilia sp, Kocuria sp, Fusarium sp, and Aspergillus sp. In conclusion, the results from this study indicate that the hospital air was generally contaminated. Therefore, the implementation of proactive policies and strategies are needed to monitor hospital air quality in sensitive zones as well as other areas of the hospitals.

Aeolian Dispersal of Bacteria Associated With Desert Dust and Anthropogenic Particles Over Continental and Oceanic Surfaces

AbstractAeolian dust is emerging as a significant vehicle for long‐range transport of microorganisms. Nonetheless, many factors relating to this highly influential dispersal mechanisms remain unresolved, including the variation in dispersal bacterial communities during stochastic desert dust events, and the effect of aeolian transit over continental and oceanic surfaces to these communities. Here we report a temporal study that encompassed multiple dust events to elucidate 16S rRNA gene‐defined changes in airborne bacterial communities at a continental‐peninsula site (Yongin, central South Korea) and a downwind offshore island site (Yonago, Honshu Island, Japan) both lying along the trajectory for dust event transport. Aerosol collected on nondust days at both sites generally reflected local origin from freshwater, marine, plant, and animal sources. At both sites, the relative abundance of spore‐forming bacteria (Bacillaceae) and organic‐aggregating bacteria (Cytophagaceae) was positively correlated with the mineral particle. Actinobacteria increased in relative abundance at the continental‐peninsula site during dust events, while marine bacterial signatures (mainly Alphaproteobacteria) were more prevalent in island site after dust events dissipated upon Japanese Sea. Overall, dust events increased the richness of airborne bacteria communities originating from inland desert and other area during early spring and are associated with more variations in airborne bacteria in the island site than the continental‐peninsula site. Airborne desert dust is likely a significant transport vehicle for bacteria. The transit of air masses over continental and marine surfaces is selective for some taxa which can be transported to distant sinks with potential impacts toward ecosystems and public health.

Bacillus-Dominant Airborne Bacterial Communities Identified During Asian Dust Events.

Asian dust (AD) events have received significant attention due to their adverse effects on ecosystems and human health. However, detailed information about airborne pathogens associated with AD events is limited. This study monitored airborne bacterial communities and identified AD-specific bacteria and the potential hazards associated with these bacteria during AD events. Over a 33-month period, 40 air samples were collected under normal atmospheric conditions (non-AD events; n = 34) and during AD events (n = 6). The airborne bacterial communities in the air samples collected during non-AD events (non-AD sample) and AD events (AD sample) were evaluated using both culture-dependent and culture-independent methods. The bacterial diversity increased significantly, along with the 16S rRNA gene copy number, in AD samples (p < 0.05) and was positively correlated with PM10 concentration. High throughput sequencing of the 16S rRNA gene revealed that the relative abundance of the phylum Firmicutes increased substantially in AD samples (44.3 ± 5.0%) compared with non-AD samples (27.8 ± 4.3%). Within the phylum Firmicutes, AD samples included a greater abundance of Bacillus species (almost 23.8%) than non-AD samples (almost 13.3%). Both culture-dependent and culture-independent methods detected common predominant species closely related to Bacillus cereus during AD events. Subsequent multilocus sequence typing (MLST) and enterotoxin gene assays confirmed the presence of virulence factors in B. cereus isolates from AD samples. Furthermore, the abundance of bceT, encoding enterotoxin in B. cereus, was significantly higher in AD samples (p < 0.05). The systematic characterization of airborne bacterial communities in AD samples in this study suggests that B. cereus pose risks to public health.