MIAMI BEACH--Russia's Mir space station has had its share of problems, from fires to dwindling oxygen supplies. But astronauts there can now worry less about one potential nightmare: the prospect that harmless microbes on Earth may evolve into killers in space. Scientists have found that common microbes in astronauts didn't multiply or change much over months aboard Mir. The findings, reported here yesterday at the American Society for Microbiology's annual meeting, also allay fears that superbugs might arise on long space flights to Mars or on the planned international space station.
The findings appear at odds with those from space shuttle missions, where two common bacteria, Escherichia coli and Staphylococcus aureus, became more resistant to antibiotics in culture. Bacteria also tended to grow more quickly in the astronauts' bodies and on the space shuttle's interior surfaces, where some species became 600 to 700 times more numerous during a mission. Coupled with evidence that astronaut immune systems are more sluggish in space, the findings raised fears that long space flights might pose a formidable risk of harmful infections.
Wondering if microbes aboard Mir showed a similar enthusiasm for space, Dwayne Pierson at NASA's Johnson Space Center in Houston and his colleagues swabbed and scraped microbe samples from three American astronauts 5 months before their Mir 18 mission in 1994. The researchers collected more samples 1 week before launch, immediately after the astronauts returned from the 115-day mission, and 1 week after touchdown. Microbiologist Henry Isenberg of the Long Island Jewish Medical Center in New Hyde Park, New York, who helped identify the specimens, says the microbes changed little in numbers or characteristics during the mission, actually decreasing slightly in two crew members. "It really surprised us; the populations were remarkably constant," Isenberg says. Experiments on the following Mir mission gave similar results.
Scientists speculate that microbe populations fresh from Earth may grow rapidly early in a Mir mission, just as they do on the shorter shuttle flights--then crash to sustainable levels, a common ecological phenomenon. Another possibility, says team member Theron Groves, a microbiologist at KRUG Life Sciences in Houston, is that astronauts aboard Mir are simply more hygienic. "They don't clean on the shuttle like they do on Mir," she says.