That ISS is laden with germs is not, honestly, much of a surprise. But some of them are highly resistant to antibiotics, and that's worrying.
The International Space Station may sound spacey-clean but it is, in fact, crawling with microbes. JPL-NASA scientists report identifying several strains of Enterobacter in samples collected from the toilet and exercise area's space station. Enterobacter is best known for infecting patients with weakened immune systems in hospitals, and being extremely resistant to antibiotics.
Luckily, the strains identified on the ISS are not pathogenic to (they do not infect) humans. And, while it's virtually impossible to have humans without bacteria – we trail our own microbiomes around wherever we go – just finding any strain of Enterobacter on the station is enough to cause concern.
The genus is infamous for its preying on immunocompromised patients here on Earth; it's also renowned for its ridiculous resistance to antibiotics. Space is an environment out of this world. There's more radiation, there's virtually no gravity, there are people everywhere, crammed up in a tube with lots of their carbon dioxide. All of these constraints could alter how microbes live and multiply – these changes could, in turn, cause them to become pathogenic to humans.
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NASA employs quite a handful of microbiologists at its Jet Propulsion Laboratory, which regularly analyzes microbe samples sent from the ISS to see if space life alters their populations or habits. The microbiologists also keep an eye on any potential biologic hazards to either equipment or astronauts' health. This is the first time they have identified the antibiotic-resistant Enterobacter strains in the station.
"To show what types of bacteria were present on the ISS, we used various methods to characterize their genomes in detail. We have revealed that genomes of five ISS Enterobacter strains were genetically most similar to three strains newly found on Earth, "explained microbiologist Kasthuri Venkateswaran.
"These three strains belonged to one species of the bacteria, called Enterobacter bugandensis, which had been found to cause illness in neonates and a compromised patient, who were admitted to three different hospitals (in East Africa, Washington State and Colorado). "
The samples were collected in 2015. Since no astronauts have been struck down since then, the bugs do not seem to be an immediate threat. However, the team says this state of affairs can quickly change – and it would be bad. The space-borne Enterobacter was found to be resistant to a wide range of antibiotics and virtually completely immune to cefazolin, cefoxitin, oxacillin, penicillin, and rifampin.
The strains also share 112 genes with clinical strains, associated with virulence, disease, and defense. The team reports that computer models show and 79% probability that the space strains will develop a human pathogen and cause disease.
Right now, however, the astronauts are safe. The possibilities, however worrying, have yet to be tested in living organisms. So the team is working to better understand the situation and develop a response procedure (that they hope never use) against these bacteria.
"Whether or not an opportunistic pathogen like E. bugandensis causes disease and how much of a threat it is, depends on a variety of factors, including environmental ones," said Venkateswaran. "Further in vivo studies are needed to discern the impact that conditions on ISS, such as microgravity, other space, and spacecraft-related factors may have on pathogenicity and virulence."
The paper "Multi-drug resistant Enterobacter bugandensis species isolated from the International Space Station and comparative genomic analyzes with human pathogenic strains" has been published in the journal BMC Microbiology.
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