According to researchers, The International Space Station (ISS) has a 'very different’ community of microbes that are more similar to that of homes than of humans.
The conclusion came from Project MERCCURI, a citizen science project that analysed bacteria found on 15 locations on the International Space Station and compared them with samples from homes on Earth as well as the Human Microbiome Project.
As per this study, Earth is surrounded by mostly harmless microbes, and a broadly similar microbial community on the ISS too.
The study said that generally, the International Space Station is habitat to at least 12,554 distinct microbial species, and the proportion of species that are closely related to known human pathogens is on par with related built environments on Earth.
The report also said that since the ISS is completely covered, the microbes inside the station come from the people on the ISS and the supplies sent to them.

Project MERCCURI
MERCCURI stands for Microbial Ecology Research Combining Citizen and University Researchers on the International Space Station (ISS). It is an association between UC Davis and other organisations, including Science Cheerleader, a group of current and former professional cheerleaders pursuing careers in science and math.