Researchers have developed an anti-microbial coating that reduced the growth of bacteria on contamination-prone surfaces at the ISS, and could help protect astronauts beyond the Moon and Mars from the antibiotic-resistant superbugs.

Microgravity, cosmic radiation, psychological stress and unearthly conditions at the International Space Station (ISS) lead to weakened immune system and strengthening of bacteria that can put the crew at risk. In the study, published in Frontiers in Microbiology journal, the team tested a new anti-microbial coating named AGXX, made of precious metals, on the toilet door. It proved to be highly effective.

After six months, no bacteria were recovered from AGXX-coated surfaces. Even at 12-19 months, just 12 bacteria were recovered -- a reduction of 80 per cent compared with bare steel. A regular silver coating tested for comparison had only a slight anti-microbial effect, reducing the number of bacteria by 30 per cent against steel.

"AGXX contains silver and ruthenium, conditioned by a vitamin derivative, and it kills all kinds of bacteria as well as certain fungi, yeasts and viruses," said Professor Elisabeth Grohmann from the Beuth University of Applied Sciences in Berlin, Germany.

"The effects are similar to bleach, except the coating is self-regenerating and never gets used up," Grohmann said.

Grohmann noted that spaceflight can turn harmless bacteria into potential pathogens as the stress hormones leave astronauts vulnerable to infection. Thus, the bacteria they carry become harder -- developing thick protective coatings and resistance to antibiotics -- more vigorous, multiplying and metabolising faster.

To make matters worse, the genes responsible for these new traits can be readily shared among different species of bacteria. "Immuno-suppression, bacterial virulence and infection risk increase with duration of spaceflight. We must continue to develop new approaches to combat bacterial infections if we are to attempt longer missions to Mars and beyond," Grohmann noted.