Scientists have been raising the alarm for years about a possible nightmare for astronauts at the international space station: antibiotic-resistant super boats that can be even more dangerous in space than they are on Earth. This week, research says they have found a way to better prevent such strong bacteria from growing on surfaces of the ISS.
The ISS and other spacecraft in the future can be an excellent breeding ground for super bacteria for various reasons. First, spacecraft are tight, busy environments, where microbial passengers (and the interchangeable resistance genes of those microbes) are constantly being shared. Second, studies have suggested that the conditions of space travel itself, such as a micro-gravity environment and low-dose radiation, may promote mutations in bacteria that make them likely to become antibiotic-resistant.
For example, some bacteria in the room develop thicker cell walls, making antibiotics less effective in killing them; others can stroll together in impenetrable biofilms. In both cases, the greater chance of survival of these bacteria can contribute to the development of more antibiotic resistance. And the immune system of astronauts is usually weaker in space, increasing the risk that these bacteria can be dangerous.
So far, that risk is theoretical. Scientists have found antibiotic-resistant bacteria in the ISS and last year a study suggested that at least some of these bacteria could cause human disease. But there is not yet a superug outbreak inspired by Ridley Scott, at least not yet.
Given the dangers of being sick in space, where medical facilities are limited, scientists have started looking for new anti-contamination instruments that are not dependent on antibiotics. The researchers behind this latest study, published in Frontiers in Microbiology, have given a new twist to an old bactericidal trick that is older than antibiotics: metal. They placed three steel plates on the ISS toilet door: one silver-coated, a well-known but decreasing antimicrobial agent that bacteria have also developed resistance to, another covered with AGXX, a new material developed by German researchers at Largentec GmbH in Berlin, and an uncoated check.
AGXX is a mix of silver and ruthenium. The developers claim that AGXX can kill bacteria and other microbes such as fungi more effectively than conventional silver, while having a lower risk of depositing silver in the environment (the metal in low doses is not considered a danger to humans, but it can for marine animals). The chemical composition of AGXX even makes it possible for the coating to regenerate itself, so that the effects last longer.
Compared to the uncoated steel of the toilet door and the silver-coated surface, AGXX seemed to be pulling its weight. After six months, no bacteria were collected from the AGXX-coated part of the door. And by the 19th month, a total of 12 bacterial strains were isolated – still a difference of 80 percent from what was collected from the uncoated steel.
"AGXX proved to be a long-term, efficient antimicrobial agent, even under the harsh conditions of the ISS," the authors wrote.
Impressive as the results were, but there were some gaps. Even in the AGXX-coated section, some antibiotic-resistant bacteria were able to grow, probably thanks to an accumulation of dead skin cells and debris that protected them from the deadly surface. And although none of the strains found in any of their tests were likely to cause a serious human disease, they were still able to form biofilms and pass through resistance genes. So although AGXX could dramatically reduce the risk of surface contamination in space, it will not even be infallible, the authors warn.
"Immunosuppression, bacterial virulence and thus risk of infection increase with the duration of space flight," said senior study author Elisabeth Grohmann, a microbiologist at Beuth University of Applied Sciences Berlin, in a statement. "We must continue to develop new approaches to combat bacterial infections if we want to try longer missions to Mars and beyond."
Grohmann and her team will continue to test AGXX on the upcoming SIRIUS 18/19 mission, a joint project between American and Russian astronauts intended to stimulate space travel in the long term. AGXX is also tested in more typical environments as a disinfectant in drinking water and elsewhere.