Astronauts aboard the International Space Station (ISS) follow a daily routine: sleep, eat meals, exercise, work. Their stay there can last anywhere from six months to a year.
During this period, the station can build a diverse range of pathogenic and non-pathogenic microorganisms that can interact with the herd. To minimize the risk of astronauts experiencing infections as a result, it is important to understand these microbes as well as antibiotics and how they interact in microgravity.
Microgravity is a strange thing. An apple fell inside the space station doesn't seem to fall because the apple and the station both fall to the ground at the same rate. Similarly, cells in microgravity are in a continuous suspension state and do not settle in the bottom of their container.
One way to restore a similar state to Earth is to continually touch the contents of the container. Another is to continually rotate the cells in a cylindrical container using a drill – a design NASA scientists hit in the 1970s. These are called high aspect ratio vessels (HARVs).
Older studies attempting to study bacteria in microgravity were short-lived and came to various conclusions: either the bacteria were more resistant or antibiotics were found to be more effective. This is not very useful.
Then a research group from the University of Houston and NASA grew Escherichia coli bacteria for a long time – 1,000 generations over six months – in microgravity.
When an antibiotic is used, some bacteria can resist it while the others break and leave a colony of antibiotic resistant bacteria.
According to Madhan Tirumalai, one of the researchers and a biologist at the University of Houston, they postponed E coli for small amounts of chloramphenicol in a HARV for two hours before rinsing repeatedly with sterile water.
At the end they found something strange. The E coli Exposed to background values of chloramphenicol appeared to be able to withstand not only chloramphenicol but also five other antibiotics that they had not been exposed to. Some bacteria also inherited the resistance over 100 generations after chloramphenicol was removed.
When the researchers inspected their DNA, they found that E coli had undergone 22 major genetic changes. The altered genes were involved in chemical pathways that control how bacteria move, attach and react to antibiotics.
In a previous study, E coli Grown for 1,000 generations in microgravity without being exposed to antibiotics, had only mutated to become better at binding to host cells.
"Room conditions are known to suppress the immunity of the astronauts," said Amit Singh, a scientist at the Indian Institute of Science, Bengaluru. "Stress in the room reduces immunity while mutated bacteria become more drug-resistant."
But if both of these mechanisms work in parallel, "astronauts are more likely to get sick of drug-resistant infections." Singh was not involved in the study.
The study has many implications, in addition to being one of the first to conclude more specifically that bacteria become more resistant to antibiotics in space than previously assumed.
Many spaceflight agencies around the world are preparing for earth orbit and moon missions, where astronauts are expected to spend more and more time in space.
Even when ISS is expected to drain the next decade, China's Tiangong space station is expected to start operating. In a similar timeframe, India will also attempt to launch its own occupied mission to Earth's orbit.
In addition, some bacteria can also survive very harsh conditions such as extreme heat and pressure. As a result, vehicles returning to the ground after time in space can bring dangerous bacteria to the ground than they are known.
The current study, published in the journal mBio January 15, 2019 studied only E coli exposed to chloramphenicol. Researchers will need to investigate interactions between a wider range of pathogens and antibiotics before we know we can keep our astronauts healthy on longer missions.
Surat Saravanan spent his PhD At Tata Institute of Fundamental Research, Mumbai, look down a microscope to understand how tissues create beautiful patterns. Currently, she writes about the science that catches her eye.