国际空间站内有多干净？

State-of-the-art molecular analysis of dust samples from the International Space Station (ISS) has been employed to reveal new information about some of the potential bacterial agents present in the astronauts' space environment. The research, published in the open access journal Microbiome, reported presence of the opportunistic bacterial pathogens that are mostly innocuous on Earth but can lead to infections that result in inflammations or skin irritations. The findings of this study help NASA establish a baseline for monitoring the cleanliness of the ISS, which will in turn help manage astronaut health in the future. However, since the study is based on genetic analysis, it could not conclude whether these bacteria are harmful to astronaut health. The ISS is a unique built environment, experiencing microgravity, space radiation and elevated carbon dioxide, and constant presence of humans. Understanding the nature of the communities of microbes -- the microbiome -- in the ISS is key to managing astronaut health and maintenance of ISS equipment. 

Traditional microbiology techniques, which culture bacteria and fungi in the lab, have previously been used to assess the composition of this community. Now scientists from NASA's Jet Propulsion Laboratory have used the latest DNA sequencing technologies to rapidly and precisely identify the microorganisms present on the ISS, filling in the gaps left by traditional methods, and highlighting pathogens that may pose a threat to astronauts.

The team collected air filter samples and vacuum bag dust from the ISS. They then compared these samples with dust from NASA 'cleanrooms', environmentally controlled and closed built spaces on Earth. Key differences between the cleanrooms and the ISS are the cleanrooms circulate fresh air while the ISS filters and recirculates air, and the ISS is inhabited continuously with only six people while 50 people may be in a cleanrooms in a day but not inhabit it continuously. Whilst these Earth cleanrooms are not air-tight, they have several layers of rooms that would prevent free exchange of air particulates.

Their results show that Actinobacteria, a type of bacteria associated with human skin, made up a larger proportion of the microbial community in the ISS than in the cleanrooms, which the authors conclude could be due to the more stringent cleaning regimes possible on Earth.

Two groups of opportunistic pathogens that can lead to infections were also found in the ISS dust samples, but the research did not address the virulence of these pathogens in closed environments or the risk of infection to astronauts.