The superbugs have colonized the International Space Station, but there is a good side


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Astronauts leave a lot behind when they go boldly. The bacteria, however, remain with them.

The extreme conditions of spaceflight can force these bacteria to harden, while simultaneously lowering the immune defenses of the stressed and isolated crew. These effects – and the risk of infection – increase with the duration of the mission.

Researchers have now taken a new step in deep space exploration by testing a new antimicrobial silver and ruthenium coating on board the International Space Station (ISS). Posted in Frontiers in Microbiology, their study shows that the AGXX has significantly reduced the number of bacteria on surfaces prone to contamination and could help protect future astronauts beyond the Moon and Mars.

A perfect storm

Microgravity. Cosmic radiation. Psychological stress. Supernatural conditions at the ISS create a perfect storm of weakened immune system and enhanced bacteria, which can put his crew at risk.

"Spaceflight can turn harmless bacteria into potential pathogens," said Professor Elisabeth Grohmann of Beuth University of Berlin. "Just as stress hormones make astronauts vulnerable to infections, the bacteria they carry become more robust – they develop thick protective coatings and antibiotic resistance – and are more vigorous, multiplying and metabolizing faster."

To make matters worse, the genes responsible for these new traits can be easily shared between different species of bacteria, either through direct contact or into the "matrix" of mud that they secrete – creating new villains, in the manner of Agent Smith.

The silver lining

To solve this problem, Grohmann and his colleagues tested a new antimicrobial coating, AGXX, on a surface prone to contamination aboard the ISS: the toilet door.

"AGXX contains both silver and ruthenium, conditioned by a vitamin derivative, and kills all kinds of bacteria, as well as certain fungi, yeasts and viruses." The effects are similar to those of the drug. bleach, with the exception of the coating that self-renews and never uses, "says Grohmann.

Silver alone has been used since prehistory to prevent microbial growth. Today, it is found in everything from socks to pools, which may explain why resistant bacteria have begun to emerge. AGXX is one of the last attempts to reinvigorate this ancient antimicrobial.

A glimmer of hope

The AGXX coating has proven to be very effective.

"After 6 months of exposure to the ISS, no bacteria was recovered on AGXX coated surfaces," reports Grohmann.

Even at 12 and 19 months, only 12 bacteria were recovered, a reduction of 80% compared to bare steel. A regular silver layer tested for comparison purposes had only a slight antimicrobial effect, reducing the number of bacteria by 30% compared to steel.

"With prolonged exposure time, some bacteria have escaped the antimicrobial action.Anti-microbial test materials are static surfaces, where dead cells, dust particles and cellular debris can occur. accumulate over time and interfere with the direct contact between the antimicrobial surface and the bacteria. "

Severe weather

"More importantly, no serious human pathogen has been detected on any surface so the risk of infection for the ISS crew is currently low," Grohmann points out.

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

"Immunosuppression, bacterial virulence and therefore the risk of infection increase with the duration of spaceflight.We must continue to develop new approaches to fight against bacterial infections if we want to try longer missions to Mars and beyond, "concludes Grohmann.

"For our part, we continue to analyze the antimicrobial performance of AGXX, most recently as part of the joint IBMP-NASA SIRIUS 18/9 isolation mission."

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More information:
Frontiers in Microbiology, DOI: 10.3389 / fmicb.2019.00543,

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