There was a time when space still felt like a distant environment, much different from our own. Now we know that space is full of the same gross issues that also plague Earth: herpes and dirty toilets plague the International Space Station, and new research shows that bacteria are just as plentiful on this orbiting petri dish as they are on the handlebars of the gym’s stationary bike.

In a paper published Monday in Microbiome, a team of microbiologists at NASA presents a complete catalog of all the bacterial communities that have thrived aboard the ISS. These characters include Staphylococcus (26 percent of all bacteria aboard the space station), Pantoea (23 percent) and Bacillus (11 percent). Of these three main characters, certain strains of staph are known to cause devastating infections in humans —specifically Staphylococcus aureus, which makes up 10 percent of the staph on the ISS.

The bacteria that live on human skin also thrive on the surfaces inside the International Space Station. Wikimedia Commons

First study author Aleksandra Checinska Sielaff, Ph.D., a post-doctoral researcher at Washington State University who collaborated with NASA’s Jet Propulsion Laboratory on this paper, explains that we don’t know whether these strains will definitely cause diseases in humans. Nonetheless, the sheer quantity of them merits closer observation:

“Whether these opportunistic bacteria could cause disease in astronauts on the ISS is unknown. This would depend on a number of factors, including the health status of each individual and how these organisms function while in the space environment,” she said on Monday.

And while these bacteria may be living in space, they didn’t come from space. They too are passengers who traveled to the ISS from Earth — 68 percent of the bacterial genera the team cataloged are present in the human gut microbiome. But many of these bacteria also dwell on the surface of our bodies. Staph, for instance, is commonly found on human skin.

Average people encounter these bacteria every day as they touch keyboards, other humans, and sweaty gym equipment where these bacterial hitchhikers are left behind. Occasionally, this contact can cause infections — for instance, football or baseball teams that share helmets and other sports equipment deal with staph outbreaks now and then.

Shared gym equipment often carries the same bacteria found on human skin, which is why it needs to be periodically cleaned. Pixabay

On Earth, our immune systems usually have what they need to fight off these infections on a day-to-day basis. But in space, the odds are stacked against us. Unnatural cycles of light and dark already upset circadian rhythms, which can lead to health complications. And even more mounting evidence is making it clear that our immune systems can’t hang with the conditions of microgravity.

A study on mice released last year found that they had significantly depleted numbers of B lymphocytes, crucial immune cells, after only 30 days in space. And human studies have shown that opportunistic viral pathogens like herpes also tend to reactivate in space, signaling that they sense weakness in the immune system.

“Specific microbes in indoor spaces on Earth have been shown to impact human health,” said lead study author Kasthuri Venkateswaran, Ph.D., a senior research scientist at JPL. “This is even more important for astronauts during spaceflight, as they have altered immunity and do not have access to the sophisticated medical interventions available on Earth,” he added.

The key is to monitor these bacteria to ensure that they don’t become infectious to humans, and more importantly, that they don’t become antibiotic-resistant. So far, the bacteria aboard the ISS seem to be safe for humans, though this study notes that they may not stay that way.

The bacteria these authors cataloged are capable of forming biofilms, communities of tight knit bacteria that, on Earth, accumulate in places like shower heads. Biofilms have been shown to promote antibiotic resistance in bacterial populations, the authors write. Even aside from health concerns, biofilms are just inconvenient. They can cause mechanical blockages or even corrosion.

If these microbes turn out to one day become infectious, antibiotic-resistant, or both, we may soon face our first real space public health challenge. But for now, it seems as if hubs for life in space like the ISS are only as bacteria-laden as the humans who go there. Before we can take the next step into colonizing space for good, we’ll have to get our own body-dwelling bacterial colonies under control first.