Air purifiers with high-efficiency particulate air (HEPA) filters remove not only particulate matter but also airborne microorganisms in indoor environments. We investigated the bacterial community in HEPA filters (used for 1 year) and that in the floor dust of 12 office rooms in Beijing. We found that the viable bacteria proportion in the filter was significantly higher than that in the floor dust (p < 0.001). The Non-Metric Multi-Dimensional Scaling analysis showed that the bacterial communities in the filters and dust were significantly different (p = 0.001). The Chao1, Shannon-Wiener and phylogenetic diversity values in the filter were significantly higher than those in the dust (p < 0.001). The predominant bacterial classes in the filter were Alphaproteobacteria and Actinobacteria, whereas those in the dust were Bacteroidia, Clostridia and Bacilli. Human occupancy contributed more to the bacterial community in the filter than that in the dust. Klebsiella and Alloprevotella in the dust and filters positively correlated with the occupancy density. Soil bacteria contributed to a significantly higher proportion of the bacteria in the HEPA filter (p < 0.001). In contrast, human oral, indoor air and outdoor haze contributed to a higher proportion of the bacteria in the dust samples (p < 0.001, p < 0.01 and p < 0.05, respectively). As HEPA filters serve as an ecological niche for indoor bacteria, they should be carefully investigated during the assessment of indoor environmental health. People spend the majority of their time indoors, wherein air pollution levels highly correlate with outdoor pollution levels 1-6. In recent years, haze pollution, fine particulate matter (PM) in particular, has been reported to increase human mortality rates owing to the development of heart disease 7,8 , stroke, respiratory disease 9 and lung cancer 10,11. The level of air pollution in China is substantially higher than in many developed countries 12. Moreover, its threat to public health has become a serious concern, particularly concerning haze events 13. Thus, an effective technology is essential for the removal of PM from indoor environments during periods of haze. To this end, air purifiers with high-efficiency particulate air (HEPA) filters are widely used in the indoor environment, particularly in areas with heavy haze 14. People are exposed to various microbes in indoor environments. Many factors could affect indoor microbial composition, including human occupancy, occupant behavior, pets and outdoor environment 15-18. The air purifier was mainly used to remove indoor PM, partly comprising microorganisms. Microbes in the air could be transmitted to the HEPA filter in the air purifier. Suzuki et al. (2003) collected swab samples from the air purifier filters in the houses of seven healthy children with varicella. They found the varicella-zoster virus was detected in 29% of filters in air purifiers by day 3 19. Furthermore, Maus et al. (2001) studied the effect of the filters on the viability of microbes. They reported microb...

Introduction: Vaccination is an essential means for prevention of tuberculosis infection, but the effects of various vaccines on the intestinal flora of mice and their response to Mycobacterium tuberculosis (Mtb) infection remain poorly understood. Methodology: In this study, two different vaccinations − ESAT6 and ESAT6 + TLR8 agonists - were administered to mice transgenic for human TLR8 to investigate gut microbiota characteristics following vaccination. Gut microbiota was investigated by next generation sequencing in the MiSeq Sequencing System. Adonis analysis was used to evaluate the effect of variables on gut bacterial community stucture. Chao1, Shannon index, and phylogenetic diversity index were used to explore the gut bacterial diversity. Results: The results showed that different vaccines have significant influence on mice intestinal bacteria (adonis analysis, p < 0.01), with gut bacterial diversity within the ESAT6 + TLR8 agonists group being significantly decreased compared to the ESAT6 treatment group (p < 0.01). Following infection with Mtb via tail vein injection, the bacterial community structure within the control versus vaccinated groups altered significantly (adonis analysis, p < 0.01), and the altered changed genera were markedly different between the groups. Following infection, Bifidobacteria differed between the groups, indicated that they play a vital role in the response to infection. Conclusions: Our results indicated that different vaccines might have distinct influences on intestinal flora, and their role should not be ignored.