The International Space Station isn't just home to a handful of astronauts. In fact, with each crew change, a new batch of bacteria joins the microbial communities that live in the station, traveling inside the astronauts' bodies, and on the surface of the objects and equipment they bring with them. In many cases, these are harmless bacteria. Inevitably, however, in 26 years of honorable service, various strains of pathogenic bacteria have also reached the ISS. And after thousands of generations, the microgravity environment has changed them, providing them with unique characteristics and very high resistance to antibiotics. This was revealed by a study published in recent weeks in the journal Microbiome by researchers from the California Institute of Technology and the Indian Institute of Technology.
The presence of resistant bacteria on the ISS is nothing new: since 2018, in fact, with the first large-scale sampling of the microorganisms that inhabit the station, it has been discovered that there is a vast bacterial community that coexists with our astronauts in space, and that some of these present a high resistance to the action of many common antibiotics. It is also known that microgravity, the high presence of CO2 and solar radiation that characterize the ISS are environmental conditions that favor the evolution of bacteria towards a greater ability to resist in extreme environments, and that this favors the development of antibiotic resistance. Combined with the fact that the same environment seems to worsen the action of the human immune system, and it is clear that the possibility of contagion in orbit with a so-called “superbug” (a multi-resistant pathogenic bacterium) worries ESA and NASA all too concretely .
For this reason, in the new study American and Indian researchers decided to study in depth the evolutionary trajectories of a species of bacteria known as Enterobacter bugandensis, of which several strains were found on the International Space Station. The researchers analyzed 13 capable of producing infections in humans, comparing their genome with that of their cousins who live on earth. The analyzes demonstrated profound differences between the bacteria collected at the station and those that live on our planet, with an average of 578 mutations that differentiate them from the genetically more similar terrestrial samples.
“Space” bacteria also present some new genetic mutations, which are practically unknown in terrestrial ones. The authors of the study believe that these characteristics are indicative of an evolution that took place in the peculiar environment of the International Space Station, and that they are therefore a response to the environmental stress to which the bacteria are subjected in the microgravity of the ISS. Focusing attention on the antibiotic susceptibility of strains collected in space, researchers have discovered in their genomes genes that confer resistance to as many as 23 different classes of drugs, including some of the most used such as cephalosporins and metronidazole.
This latest discovery, according to the researchers, is of particular importance, because the strains of Enterobacter bugandensis present on the ISS appear to be extremely adapted for life on the space station, capable of coexisting with many other species of bacteria, and possessing a very high resistance to antibiotics. All details that raise fears that the genes that confer antibiotic resistance could easily spread in the ISS microbiota, and could therefore represent a risk to the health of astronauts in the future.