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Relative abundances of bacteria in the indoor air, ventilation duct air, floor dust, and HVAC filter dust samples. Relative abundances of the 20 most common bacterial taxa in indoor air, ventilation duct air, HVAC filter dust, and floor dust. Indoor and ventilation duct air include PM 10 samples from indoor air when the 

Relative abundances of bacteria in the indoor air, ventilation duct air, floor dust, and HVAC filter dust samples. Relative abundances of the 20 most common bacterial taxa in indoor air, ventilation duct air, HVAC filter dust, and floor dust. Indoor and ventilation duct air include PM 10 samples from indoor air when the 

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Exposure to specific airborne bacteria indoors is linked to infectious and noninfectious adverse health outcomes. However, the sources and origins of bacteria suspended in indoor air are not well understood. This study presents evidence for elevated concentrations of indoor airborne bacteria due to human occupancy, and investigates the sources of t...

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... shown in Figure 1. Occupancy results in an increase in airborne concentrations of both total particle mass and bacterial genome copy numbers (GCN). For indoor PM 10 , mass increased by 15 times ( p = 0.00001) and GCN increased by 66 times ( p = 0.001) for occupied conditions compared with the vacant case, while smaller increases of 2.5 times ( p = 0.015) and 16 times ( p = 0.02) occurred in PM 2.5 mass and GCN, respectively. Ratios 6 standard error of PM 10 to PM 2.5 mass concentrations were 4.9 6 0.3 for indoor occupied air, 0.8 6 1.2 for indoor unoccupied air, 1.2 6 0.9 for occupied outdoor air and 1.1 6 0.9 for vacant outdoor air, respectively, indicating a strong influence on respirable particles larger than 2.5 m m for the indoor environment when occupied, and substantiating the expectation that occupancy is an important contributor to suspended coarse particulate matter [24]. To elucidate potential sources of increased aerosol concentrations during occupancy, experiments were conducted to investigate separately the impacts of resuspension from the carpet during walking and direct shedding from humans. The ratio of the indoor particle number concentration to the outdoor particle number concentration for three experimental conditions are presented in Figure 2. These conditions included (a) one person walking on the carpet, (b) one person walking on the same floor covered with plastic sheeting to eliminate resuspension of particles from the carpet, and (c) 30 adults occupying the room while the carpet was covered with plastic sheeting. For condition (c), occupants were allowed to moved freely about the room and activities centered on talking, reading, and writing. The results in Figure 2 suggest that significant particle generation in the occupied test room may occur through resuspension of dust deposited on the floor, through direct shedding of particles from human occupants, or both. Cases (a) and (c) resulted in particle number concentrations that were greater than the outdoor concentrations for all size ranges. In case (a) when the carpet was not covered with plastic sheeting (resuspension), these increases were 1.2 to 11 times across the range of particle sizes with an average increase of 5.2 times ( p = 0.05). In case (c), proportional increases of 1.2–4.5 times with an average of 2.7 times ( p = 0.18) were observed for the floor covered with plastic when the occupancy level was 30 people. Case (c) is suggestive of shedding rather than resuspension. In both cases, the proportional extent of particle concentration increase rose monotonically with increasing optical particle size throughout the instrument’s measurement range. A comparison of the bacterial mass percentage of airborne particle and floor dust samples is shown in Figure 3. Estimates of bacterial mass were computed assuming the mass of a bacterium to be 655 femtograms [25], and an average 16 S rDNA gene copy number of four per bacterium [26]. Results displayed in Figure 3 demonstrate that the PM 10 and PM 2.5 fractions of resuspended floor dust are enriched with bacteria, compared to indoor air, ventilation duct supply air, and outdoor air. The median bacterial mass percentages of indoor and outdoor airborne particles were less than 0.3%, whereas the bacterial proportion of aerosolized floor dust exceeded 2.2% in both size fractions. Based on a Tukey’s range test, resulting ranks for bacterial abundance in both PM 2.5 and PM 10 cases are resuspended floor dust & outdoor air . duct supply air . indoor air. However, only differences between resuspended floor dust and the three air samples were statistically significant at a 95% confidence level. Sixteen samples from indoor air, ventilation duct supply air, floor dust, and HVAC filter dust (Table 1) were analyzed for bacterial population composition using the 454 GS-FLX pyrosequencing platform with multiplex identifiers (MIDs). Sample MIDs are presented in Table S1. After machine- and method- based quality control, denoising, and chimera checking, 10,675 partial 16 S rDNA gene sequences were generated at an average trimmed length of 500 base pairs (bp). Rarefaction values based on 97% similarity were produced for each sample and were then averaged based on their sample type (Figure S2). Rarefaction curves of observed OTUs continued to rise with increasing numbers of sequences, suggesting that further increases in sample size would yield more species. Chao1 richness estimator predicted 3720, 1260, 2990, and 640 OTUs, respectively, for floor dust, HVAC filter dust, indoor air, and ventilation duct supply air (Figure S1). The diversity metrics reported here are higher than those previously determined for floor dust, which ranged from 83 to 464 based on the Chao1 approach in conjunction with a cloning and Sanger sequencing method [20,27]. The relative abundances of the 20 most prominent bacterial taxa from indoor air, ventilation duct supply air, HVAC filter dust, and floor dust are shown in Figure 4. (Phyla level data are presented in Figure S3.) Indoor air, ventilation duct supply air, and floor dust samples show heavy representation from the dominant bacteria previously found to be associated with human skin, hair, and nostrils [28,29,30,31,32]. These five human associated taxa — Proprionibacterineae , Staphylococcus , Streptococcus , Enterobacteriaceae , and Corynebacterineae — comprise 17%, 20%, and 17.5% of all bacteria in samples of indoor air, floor dust, and ventilation duct supply air, respectively. The HVAC filter dust sample demonstrated significant differences from all other samples, being strongly dominated by the Streptophyta phylum (chloroplast 16 S rRNA encoding gene from plants) with only minor (3%) representation from the five human-associated taxa described above. To quantitatively compare populations, the similarities and differences between the sample bacterial community structures are presented in relation to principal coordinate analysis (see Figure 5A) on a weighted-UniFrac basis. Stemming from p -test significance evaluation using the Bonferroni correction for multiple comparisons, the bacterial communities characterized in indoor air and duct air during human occupancy were significantly different from the communities collected on the HVAC filter dust sample ( p , 0.001). Differences were not statistically significant between indoor air and ventilation supply duct air bacterial communities ( p . 0.1), or between ventilation supply duct air and floor dust communities ( p . 0.1). Indoor air bacterial communities reveal almost significant differences compared to those of floor dust (0.05 , p , 0.1). Figure 5B displays the indoor air, ventilation supply duct air, HVAC filter dust, and floor dust samples in this study along with other samples from published studies on the microbial diversity of potential sources including floor dust, human skin, and outdoor air. In all, 104 samples were evaluated for this comparison: 16 samples from the present study; 12 floor dust samples from nursing homes and private residences [20,27]; 15 outdoor air samples taken in areas with varying land use types including urban, rural, and agricultural sites [33]; and 61 human skin samples from two female and two male individuals sampled at different times including left and right palms, index fingers and forearms [31]. The weighted UniFrac analysis, which encompasses several different environments, demonstrates distinct groupings for aerosol samples, for human skin samples, and for floor dusts samples. The data show broad similarities among outdoor and indoor aerosol bacterial ecology, likely owing to the presence of many environmentally associated organisms in the indoor air samples taken in this study (Figure 4). Larger differences are observed in floor dust samples across studies, with the floor dust measured here (open blue circles) residing more closely to aerosol samples, and floor dust from nursing homes and private residences (closed blue circles) [20,27] clustering more closely to human skin samples than to aerosol samples. This study advances knowledge about the sources, origins, and character of bacterial aerosols in indoor settings through two main findings. First, human occupancy produces a marked concentration increase of respirable particulate matter and bacterial genomes. Second, bacteria from human skin and from ...
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... samples is shown in Figure 3. Estimates of bacterial mass were computed assuming the mass of a bacterium to be 655 femtograms [25], and an average 16 S rDNA gene copy number of four per bacterium [26]. Results displayed in Figure 3 demonstrate that the PM 10 and PM 2.5 fractions of resuspended floor dust are enriched with bacteria, compared to indoor air, ventilation duct supply air, and outdoor air. The median bacterial mass percentages of indoor and outdoor airborne particles were less than 0.3%, whereas the bacterial proportion of aerosolized floor dust exceeded 2.2% in both size fractions. Based on a Tukey’s range test, resulting ranks for bacterial abundance in both PM 2.5 and PM 10 cases are resuspended floor dust & outdoor air . duct supply air . indoor air. However, only differences between resuspended floor dust and the three air samples were statistically significant at a 95% confidence level. Sixteen samples from indoor air, ventilation duct supply air, floor dust, and HVAC filter dust (Table 1) were analyzed for bacterial population composition using the 454 GS-FLX pyrosequencing platform with multiplex identifiers (MIDs). Sample MIDs are presented in Table S1. After machine- and method- based quality control, denoising, and chimera checking, 10,675 partial 16 S rDNA gene sequences were generated at an average trimmed length of 500 base pairs (bp). Rarefaction values based on 97% similarity were produced for each sample and were then averaged based on their sample type (Figure S2). Rarefaction curves of observed OTUs continued to rise with increasing numbers of sequences, suggesting that further increases in sample size would yield more species. Chao1 richness estimator predicted 3720, 1260, 2990, and 640 OTUs, respectively, for floor dust, HVAC filter dust, indoor air, and ventilation duct supply air (Figure S1). The diversity metrics reported here are higher than those previously determined for floor dust, which ranged from 83 to 464 based on the Chao1 approach in conjunction with a cloning and Sanger sequencing method [20,27]. The relative abundances of the 20 most prominent bacterial taxa from indoor air, ventilation duct supply air, HVAC filter dust, and floor dust are shown in Figure 4. (Phyla level data are presented in Figure S3.) Indoor air, ventilation duct supply air, and floor dust samples show heavy representation from the dominant bacteria previously found to be associated with human skin, hair, and nostrils [28,29,30,31,32]. These five human associated taxa — Proprionibacterineae , Staphylococcus , Streptococcus , Enterobacteriaceae , and Corynebacterineae — comprise 17%, 20%, and 17.5% of all bacteria in samples of indoor air, floor dust, and ventilation duct supply air, respectively. The HVAC filter dust sample demonstrated significant differences from all other samples, being strongly dominated by the Streptophyta phylum (chloroplast 16 S rRNA encoding gene from plants) with only minor (3%) representation from the five human-associated taxa described above. To quantitatively compare populations, the similarities and differences between the sample bacterial community structures are presented in relation to principal coordinate analysis (see Figure 5A) on a weighted-UniFrac basis. Stemming from p -test significance evaluation using the Bonferroni correction for multiple comparisons, the bacterial communities characterized in indoor air and duct air during human occupancy were significantly different from the communities collected on the HVAC filter dust sample ( p , 0.001). Differences were not statistically significant between indoor air and ventilation supply duct air bacterial communities ( p . 0.1), or between ventilation supply duct air and floor dust communities ( p . 0.1). Indoor air bacterial communities reveal almost significant differences compared to those of floor dust (0.05 , p , 0.1). Figure 5B displays the indoor air, ventilation supply duct air, HVAC filter dust, and floor dust samples in this study along with other samples from published studies on the microbial diversity of potential sources including floor dust, human skin, and outdoor air. In all, 104 samples were evaluated for this comparison: 16 samples from the present study; 12 floor dust samples from nursing homes and private residences [20,27]; 15 outdoor air samples taken in areas with varying land use types including urban, rural, and agricultural sites [33]; and 61 human skin samples from two female and two male individuals sampled at different times including left and right palms, index fingers and forearms [31]. The weighted UniFrac analysis, which encompasses several different environments, demonstrates distinct groupings for aerosol samples, for human skin samples, and for floor dusts samples. The data show broad similarities among outdoor and indoor aerosol bacterial ecology, likely owing to the presence of many environmentally associated organisms in the indoor air samples taken in this study (Figure 4). Larger differences are observed in floor dust samples across studies, with the floor dust measured here (open blue circles) residing more closely to aerosol samples, and floor dust from nursing homes and private residences (closed blue circles) [20,27] clustering more closely to human skin samples than to aerosol samples. This study advances knowledge about the sources, origins, and character of bacterial aerosols in indoor settings through two main findings. First, human occupancy produces a marked concentration increase of respirable particulate matter and bacterial genomes. Second, bacteria from human skin and from ...

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... Occupant bioaerosol emissions are due to direct respiratory emissions, shedding/resuspension from skin and clothing, and resuspension from surfaces in the room, of which resuspension from surfaces is the largest fraction [14,15]. Hospodsky et al. [10] reported that occupancy in a classroom resulted in an approximately 66-fold increase in PM 10 airborne bacterial genome compared to an unoccupied classroom, and Qian et al. [11] reported a 5-fold increase in indoor airborne fungal concentrations due to occupancy in the same classroom. The time-integrated bioaerosol emission factor, presented in colony-forming units (CFU) per hour, was measured for a number of bacteria and fungi in a middle school. ...
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Esta obra constituiu-se a partir de um processo colaborativo entre professores, estudantes e pesquisadores da área da microbiologia que reuniram alguns dos seus resultados recentes de pesquisas com foco na obtenção de produtos microbianos de interesse biotecnológico. Resulta também, de um movimento interdisciplinar trazendo como aliada a fotografia científica, onde a imagem da capa foi produzida a partir de um ensaio fotográfico para registro artístico da beleza e sutileza do trabalho executado na rotina de um laboratório de microbiologia, apresentando uma das Actinobactérias objeto de estudo nesta obra, trazendo portanto, a identidade deste livro. Esta iniciativa se construiu a partir de um movimento interdisciplinar e interinstitucional reunindo ações de incentivo à pesquisa que uniu pesquisadores de diferentes especialidades dentro da grande área da Microbiologia de instituições de ensino superior públicas e privadas, nacionais e internacionais. As informações aqui apresentadas tem a finalidade de estimular a leitura sobre a vivência da biotecnologia microbiana em nossa rotina e, portanto, fomentar a formação científica por meio da produção, socialização e estímulo de acesso ao conhecimento especializado. Agradecemos aos autores pela disponibilidade, empenho e dedicação para o desenvolvimento dessa obra, especialmente por aceitarem este desafio em um momento delicado que vivemos em reclusão devido à Pandemia de COVID-19. Esperamos também que esta obra sirva de instrumento didático-pedagógico para estudantes, professores dos diversos níveis de ensino em seus trabalhos e demais interessados pela temática.