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Silver Keeps the ISS Healthy for Astronauts

Harmful bacteria can survive in space under zero-gravity conditions. That can make for some pretty unhealthy living and working conditions on the International Space Station (ISS), which has been continually inhabited since November 2000.

One of the areas which scientists found particularly rife with bacteria is the toilet door. Such infestations are more dangerous for astronauts in space because prolonged time in orbit has been shown to reduce a person’s immune system. Microgravity, along with solar and cosmic radiation, changes the immune-regulatory system of the crew, leaving them more susceptible to pathogens.

“Spaceflight can turn harmless bacteria into potential pathogens,” said senior study author Elisabeth Grohmann of Beuth University of Applied Sciences, Berlin, in a prepared statement. “Just as stress hormones leave astronauts vulnerable to infection, the bacteria they carry become hardier -developing thick protective coatings and resistance to antibiotics and more vigorous, multiplying and metabolizing faster.”

The safest and perhaps simplest way to get rid of the microbes is a coating of silver and ruthenium, according to astronauts who tested the new combination. The surface coating is called AgXX. (Ruthenium is a rare metal belonging to the platinum group of the periodic table and is inert to most other chemicals. The element offers some antibacterial powers.)

AgXX works by killing bacteria as well as certain fungi, yeasts and viruses, Grohmann noted. “The effects are similar to bleach except the coating is self-regenerating, so it never gets used up.”

After coating the door to the space toilet with AgXX, the space station astronauts tested the surface for bacteria three times over a 19-month period. After the first six months, the AgXX-coated surface remained bacteria-free. However, six months later, nine strains of bacteria were found and three more strains were discovered by the end of the study period.

In the long term, the AgXX-coated surface had 80 percent fewer bacterial strains compared to an uncoated area of bare steel. Interestingly, the coating’s germ-killing powers were lessened but not because the material itself became less effective. Instead, a build-up of dust and dirt decreased the coating’s ability to make contact with bacteria.

“With prolonged exposure time a few bacteria escaped the antimicrobial action. The antimicrobial test materials are static surfaces where dead cells, dust particles and cell debris can accumulate over time and interfere with the direct contact between the antimicrobial surface and the bacteria,” Grohmann explained.

NASA astronaut Serena Auñón-Chancellor, who handles plumbing aboard the ISS, said: “Most importantly, no serious human pathogens such as Methicillin-resistant Staphylococcus aureus (MRSA) or Vancomycin-resistant Enterococci (VRE) were found on any surface. Thus, the infection risk for the crew is low.”

“Immunosuppressant, bacterial virulence and therefore infection risk increase with duration of spaceflight,” Grohmann added. “We must continue to develop new approaches to combat bacterial infections if we are to attempt longer missions to Mars and beyond.” The researchers’ results are in the journal Frontiers in Microbiology.

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