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Astronauts aboard the International Space Station (ISS) live and work in a hyper-organized place full of computers and laboratory experiments. Neighborhoods are confined and clean.
But at the microscopic level, the ISS, like our homes and workplaces, is teeming with bacteria.
And in space, microgravity (weightlessness), cosmic radiation and psychological stress can weaken the immune system of astronauts and, at the same time, propel bacteria to become stronger.
A study by German scientists, published in the journal Frontiers in Microbiology, showed that an antimicrobial coating based on silver and ruthenium significantly reduced the number of bacteria on surfaces prone to contamination in the environment. ; ISS.
The coating, called AGXX and manufactured by the German company Largentec Vertriebs in Berlin, could help protect future astronauts.
Here on Earth, the coating undergoes tests for possible use in hospitals and medical and hydraulic systems applications.
Elisabeth Grohmann, PhD, is the lead author of the study. She is Professor of Microbiology in the Department of Life Sciences and Technology at the Beuth University of Applied Sciences in Berlin.
"Spaceflight can turn harmless bacteria into potential pathogens," she told Healthline. "Just like stress hormones make astronauts vulnerable to infections, the bacteria they carry become more resistant – develop thick protective coatings and antibiotic resistance – and more vigorous, multiply and metabolize faster."
In addition, the genes responsible for these new traits can be easily shared between different species of bacteria by direct contact or in the "matrix" of mud they secrete, she says.
Grohmann and his colleagues conducted their study from 2013 to 2015.
The members of the ISS team applied the AGXX on the outside surface of the toilet door. The performance tests of the coating were carried out after 6, 12 and 19 months.
"We have successfully applied AGXX, a new antimicrobial material, which can be used as a coating for virtually all types of materials, from metals to plastic," said Grohmann.
"It greatly reduces the growth of bacteria, including many dangerous pathogenic bacteria. The coating kills bacteria by importing toxic and highly reactive substances (reactive oxygen species) into bacterial cells. These substances attack the biomolecules of the bacterial membranes, thus killing the bacteria, "she explained.
After six months, no bacteria were recovered from the ISS coated surfaces.
According to Mr Grohmann, even at 12 and 19 months, a total of 12 bacteria were recovered, a reduction of 80% compared to uncoated surfaces.
A regular silver coating tested for comparison purposes had only a slight antimicrobial effect and reduced the number of bacteria by 30%.
"With the prolonged exposure time, some bacteria have escaped the antimicrobial action," she said. "Antimicrobial test materials are static surfaces, where dead cells, dust particles and cellular debris can accumulate over time and interfere with direct contact between the surface of the antimicrobial and the bacteria. "
AGXX contains both silver and ruthenium conditioned by a vitamin derivative. It kills many bacteria as well as some fungi, yeasts and viruses, says Grohmann.
The effects are similar to those of bleach, with the difference that the coating is self-regenerating and is never used, she adds.
"But I want to point out that the study was initiated not because of crew member health problems, but because of the corrosion of materials on the ISS caused by microbial growth and biofilms on rubber seals, on observation windows and on different material surfaces, "said Grohmann. .
David Coil, PhD, a microbiologist and project scientist at the University of California at Davis, has also participated in published studies on bacteria on the ISS.
"In the first study, we took a group of bacteria from the Earth and compared their growth on the ISS and on Earth. We found that almost all bacteria grew very similar, one of them developing better in the space. We have not looked at antibiotic resistance, the formation of biofilms or anything like that, "he told Healthline.
"The second was a sequencing survey of the ISS's DNA. We examined which bacteria were present on the surfaces of the ISS. Our main message to remember was that the ISS was dominated by bacteria badociated with humans and actually looked like a house on Earth, "he added.
The antimicrobial coating seems to work well on Earth and on the ISS, he said, but the recent study is presented "in a more alarmist context than I think is justified," said Coil.
"There is indeed work showing that bacteria behave differently on the ISS (formation of biofilms, etc.), but virtually none of these works has been translated by a real increase in virulence or risk, "he said. "Most of the results, both in this document and referenced by this one, lack appropriate context."
The authors of the study said that 60% of their bacterial strains had resistance to three or more antibiotics, Coil said.
But this discovery means nothing without comparison with equivalent constraints on Earth, he notes.
"All" human pathogens "belong to groups known to form biofilms, resist antibiotics and undergo horizontal gene transfer," said Coil.
"What they really mean are organisms belonging to groups known to contain pathogens. Think about E. coli. It can be a pathogen or a bacterium important and beneficial in humans. I find it very misleading to report only this type of data from the ISS. It's easy to infer that these traits are "because" the bacteria were from the ISS, Coil said.
Coil says the study does not discuss the idea of neutral and beneficial bacteria either.
Is it a good idea to kill everything on board the ISS? "Probably not," Coil said.
Evidence provided by hospitals shows that when medical staff strive to create a sterile environment, these environments tend to colonize with the most resistant and potentially most dangerous organisms, he said.
"Yes, astronauts have had an impact on immune function in the space," said Coil. "And yes, some bacteria behave differently on the ISS. But I do not think it's justified to say, for example, "Spaceflight can turn harmless bacteria into potential pathogens," said Coil.
"Of course, she says" potential ", but I still think the average reader of this sentence would understand the idea that spaceflight makes these bugs dangerous. I do not see proof of that, "he continued.
"Although I think the data in this document is correct," said Coil, "I think that they are framed in a context that is very scary and that they might not be the type of solution that we wish anyway. "
Nevertheless, the antimicrobial coating could still have a promising future in space and on Earth.
"AGXX is being tested for future applications, such as the coating of catheters for urine. The first successful study was conducted for several years, but has not been published yet, "Grohmann said.
"Other tests involve its use as an antimicrobial coating for wound dressings, as a component of eliminating ointments and lotions and water filtration systems." . A next test will try to eliminate the germs in the filters for air conditioners, "she added.
Another current test examines the effect of AGXX on bacterial endospores, the most resistant life form of certain bacteria, and on pathogenic viruses for humans likely to cause disease, she says.
The Institute of Biomedical Problems of the Russian Academy of Sciences in Moscow has just inaugurated a four-month isolation study using an antimicrobial coating in an inhabited habitat , a pretest and preparatory research for future lunar and Martian expeditions, explains Grohmann.
The study is funded by the European Space Agency and NASA.
The objective is to identify bacteria that survive on antimicrobial-covered areas and to badess potential health risks to crew members including antibiotic resistance, toxin production, virulence factors and the formation of biofilms.
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