Study Shines Light on Antibiotic Use in Space

Jan. 15, 2019
Tuesday, Jan. 15, 2019

Washington, D.C. – January 15, 2019 – Antibiotics should be used sparingly in the space environment, according to a new study published this week in the journal mBio. The study found that using antibiotics as a preventive measure in a simulated microgravity environment could be counterproductive and will likely result in persistent resistance to antibiotics.
“The key finding of our study is that bacteria very rapidly become resistant to antibiotics in a simulated microgravity environment. Once exposure to an antibiotic ceases, the bacteria continue to be resistant for significant periods of time, so once you have made bacteria resistant, it doesn’t become nonresistant,” said the study’s principal investigator George E. Fox, Ph.D., Moores Professor of Biology and Biochemistry and Chemical and Biomolecular Engineering, in the Department of Biology and Biochemistry, University of Houston, in Texas. “The bottom line message is you want to avoid using antibiotics as much as possible in the space environment, as well as in the earth environment.”
Minimizing antibiotic resistance is desirable in the space environment, because stress factors during space, including microgravity, sleep deprivation, radiation, isolation and microbial contamination, can promote immune suppression. Especially during long-term missions, these conditions can increase the risk of infection from opportunistic pathogens.
Researchers at the University of Houston, collaborating with researchers at the National Aeronautics and Space Administration, launched their study, in part, because there is a question of whether using antibiotics on the International Space Station can have unintended consequences. The long-term response of microbial communities to the microgravity environment of space is not fully understood. “The question is what happens if you expose bacteria in the space station to an antibiotic? You might want to consider coating a small area in the space station with an antibiotic to prevent fungus from growing, for example,” said Dr. Fox. 
In the new study, researchers grew Escherichia coli cells under low shear modeled microgravity conditions for over 1,000 generations using an antibiotic chloramphenicol treatment between cycles to prevent contamination. “The rotation vessel we use in our study simulates microgravity, and the bacteria are in continuous freefall. When you are in space, gravity disappears, and this simulates that,” said Dr. Fox. “We were using chloramphenicol to disinfect the apparatus with the result that the bacteria rapidly become resistant to chloramphenicol. 
In addition to acquiring resistance to chloramphenicol, the adapted strain acquired resistance to cefalotin, cefuroxime, cefuroxime axetil, cefoxitiin, and tetracycline. Resistance to chloramphenicol and cefalotin persisted for over 110 generations, despite the removal of both the low microgravity conditions and trace antibiotic exposure. Genome sequencing of the adapted strain revealed 22 major changes, including those involved in bacterial adhesion, motility, and chemotaxis (movement of a cell or organism in a direction corresponding to a gradient of increasing or decreasing concentrations of a particular substance).
“This study shows that bacteria in space are going to become resistant to antibiotics, so you want to be very careful about using antibiotics,” said Dr. Fox. “Unintended resistance to other antimicrobials might also occur as well as permanent genome changes that may have other unanticipated and undesirable consequences.”
The study is unique in that it examines roughly 1,000 generations of bacteria. “Previous studies have just been short-term, two or three days. This study and our earlier study are the first time that anybody created this model of microgravity environment and examined bacteria after 1,000 generations,” said Dr. Fox. The earlier study found that cells grown under identical conditions without antibiotic exposure did not acquire antibiotic resistance.
The findings of the new study are important given a renewed or heightened interest in space, perhaps sparked by the realization that humans are fast making their planet uninhabitable. The durations for planned missions to space range from roughly a month for lunar missions, one year on the ISS, to 30 months on Mars (Design Reference Mission). Efforts to understand the possible negative effects of the space environment on human physiology and immune function are seen as a high priority by NASA. “There is a lot of interest in going to Mars. The Chinese are sending somebody to the dark side of the moon. There is a lot of interest in space,” said Dr. Fox.
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