Looking up at the night sky brings to mind flights of fancy and traveling through space on far off adventures. In reality, astronauts on the International Space Station (ISS) are still learning the challenges of long-term space travel and living in space.

One of those challenges includes maintaining a healthy work environment that is clean and free of potential dangers to the health of astronauts.  

During the first decade of the 21st-century studies on the health of astronauts revealed a unique set of challenges. In space microgravity, solar and cosmic radiation weaken the immune system, this, in turn, makes the astronaut more susceptible to bacterial infections.

Conversely, mounting studies are telling us that bacteria in space become more virulent and pathogenic. Bacteria have a greater tendency to form biofilms, which are bacteria that form protective layers, making them less susceptible to the environment and by their composition, resistant to chemical penetration and antibiotics.

Obtaining swabs from various surfaces on the ISS has revealed that the long-term space habitat is teeming with microbial life. But this isn’t a big surprise, studies in the early 21st century examining the MIR space station identified 234 bacterial and fungal species. These early studies revealed that finding microbes on spacecraft including the ISS would be inevitable. A recent study has shed more light on these space stowaways, revealing they harbor dangerous antibiotic resistance genes on plasmids. Plasmids are small pieces of mobile DNA, smaller than bacterial genomes and encode various antibiotic resistance genes capable of moving into different bacteria and conferring resistance. The researchers also found that most of these drug-resistant isolates can form biofilms.  

These dangerous combinations of traits presents a major risk to astronauts who live in enclosed habitats for extended periods of time where these pathogens can survive. The limited access to medical intervention available in space coupled with the dwindling number of antibiotic options left here on earth mean an innovative solution must be discovered. At the same time these are challenges we face everyday in hospital settings. Hospital surfaces and medical equipment are notorious for transmitting bacteria and harboring bacteria in biofilms. The transfer of these organisms to hospital patients with already weakened immune systems means they are likely to get an infection all while being in the hospital for what is most commonly an unrelated health issue.

Researchers working in antimicrobial development have engineered an innovative coating to keep surfaces free of bacterial contamination. This invention which is named AGXX is a metal-based surface coating capable of preventing microbes from colonizing surfaces. The AGXX coating is an alloy of silver and ruthenium and employs nanotechnology-based metals to create an advanced coating. Nanotech research has produced these next-generation metals, far superior to traditional metals in their uniformity and almost universal application. Nanometals have been incorporated into many everyday human use products like yoga mats, underwear, and bedsheets, but their potential effects on human health raise questions about safety and toxicity. These nanometals are small enough to penetrate human cells as well as bacteria.  The other concern is the rise of resistant mutants. Just like other solutions developed against bacteria, the organisms may figure out a way to circumvent or become resistant to these metal alloys.

For thousands of years traditional metals like copper and silver were used as containers for food and water, however, after the discovery of the first antibiotics, metal research in this area began to lose favour. Today, in the grip of so few antibiotic options, metals have once again become an area of intense research. The AGXX coating is thought to kill bacteria by the generation of reactive oxygen species which damage biological molecules like proteins, DNA and lipids. Studies using the AGXX coating such as one performed on the ISS have shown bacteria are unable to survive on surfaces sprayed with these coatings compared to silver or stainless steel. The AGXX coating was compared to a silver coating and stainless steel and placed on the ISS in frequently visited areas. Over the course of 19 months, only 8 pathogenic isolates were recovered from the AGXX coated surface compared to 28 from the silver coated surface and 42 from the stainless steel surface.

The isolated strains were tested for biofilm formation, most strains were able to produce biofilms. Additionally, most of the strains isolated were multidrug resistant, traits commonly found on isolates obtained from the space stations in previous studies. Why most isolates were found to express these dangerous characteristics is not clear, but the strains likely originated from mission astronauts and crew members helping on earth. Further studies will be required to understand why pathogenicity and virulence increase in microgravity environments.

In the meanwhile, antimicrobial coatings will continue to be explored as preventative mechanism to bacterial contamination while their safety profiles are monitored and studied.

Original research article: "Biofilm Forming Antibiotic Resistant Gram-Positive Pathogens Isolated From Surfaces on the International Space Station" 

Front. Microbiol, 2019, doi: 10.3389/fmicb.2019.00543

Dr. Dinesh M Fernando

@Dineshmfernando