Eliminating superbugs on the International Space Station

An antimicrobial coating made of precious metals has reduced growth of bacteria on contamination-prone surfaces inside the International Space Station (ISS), where extreme conditions can foster antibiotic-resistant superbugs.

When astronauts leave Earth, bacteria stay with them, remaining with them through spaceflight and on the unearthly conditions of the ISS. This creates a perfect storm of weakened immune system and strengthened bacteria, which can put crew at risk. Furthermore, these effects — and the risk of infection — grow with mission duration, and the genes responsible for these new traits can be readily shared among different species of bacteria.

“Spaceflight can turn harmless bacteria into potential pathogens,” said Professor Elisabeth Grohmann of Beuth University of Applied Sciences Berlin. “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 metabolising faster.”

To address this problem, Prof Grohmann and her colleagues tested a silver- and ruthenium-based antimicrobial coating, known as AGXX, on a contamination-prone surface aboard the ISS: the toilet door. Silver on its own has been used since prehistory to prevent microbial growth, and today it is found in everything from socks to swimming pools — which is, ironically, perhaps why resistant bacteria have begun to emerge.

“AGXX contains both silver and ruthenium, conditioned by a vitamin derivative, and it kills all kinds of bacteria as well as certain fungi, yeasts and viruses,” Prof Grohmann said. “The effects are similar to bleach — except the coating is self-regenerating so it never gets used up.”

Published in the journal Frontiers in Microbiology, the study showed that the AGXX coating proved to be highly effective, dramatically reducing the number of bacteria on contamination-prone surfaces. Prof Grohmann said, “After six months’ exposure on the ISS, no bacteria were recovered from AGXX-coated surfaces.”

Even at 12 and 19 months, a total of just 12 bacteria was recovered — a reduction of 80% compared to bare steel. A regular silver coating tested for comparison had only a slight antimicrobial effect, reducing the number of bacteria by 30% versus steel.

“With prolonged exposure time a few bacteria escaped the antimicrobial action,” Prof Grohmann said. “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.

“Most importantly, no serious human pathogens were found on any surface. Thus, the infection risk for the ISS crew currently is low.”

Nevertheless, all bacterial isolates were able to form immunity-evading slimy coatings, and most were resistant to at least three antibiotics. They were also able to share the genes responsible.

“Immunosuppression, bacterial virulence and therefore infection risk increase with duration of spaceflight,” Prof Grohmann said. “We must continue to develop new approaches to combat bacterial infections if we are to attempt longer missions to Mars and beyond.”

Image credit: ©stock.adobe.com/au/cosmicvue

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