New study reveals exactly how much unknown bacteria is covering your phone and shoes

Photo: John Voo

Considering everything that’s happened this year, you’re probably already spending a bit more time focusing on keeping your smartphone clean. Just in case you needed some extra motivation to break out the anti-bacterial wipes every once and a while, look no further than a recent study released by the University of California, Davis.

UCD researchers just performed the largest study ever on bacteria found residing on people’s phones and shoes, and the results were eye-opening, to say the least. Thousands of different forms of bacteria were found all over examined phones and shoes. Moreover, many of those bacteria groups are considered “microbial dark matter,” meaning they’re barely known to modern science at all.

Yup, that means the next time you use your phone then touch your face there’s a decent chance you’re spreading some bacterial dark matter all over your cheeks. While all of that is enough to make most of us throw our phones in the trash and start using a beeper again, there’s a silver lining to these findings. As far as the study’s authors can tell, the vast majority of bacteria found on our shoes and phones, unknown to modern science or not, appear to be largely harmless.

“This highlights how much we have to learn about the microbial world around us,” says first study author David Coil, a researcher at the University of California, Davis Genome Center, in a press release.

It’s not something any of us want to dwell or focus on all too often, but our planet is covered in communities of bacterial microbes, referred to as microbiomes. Similarly, every person has a personal collection of bacteria, or microbiome, of their own. Ultimately, though, most of the bacteria found among and inside us are either benign or even beneficial. 

To try and get a better sense of typical bacteria found on people’s phones and shoes, the research team started collecting microbe samples from fans attending sporting events all over the country back in 2013-2014. At the time, each volunteer had their cell phone and shoes swabbed for bacterial samples. In all, samples were collected from nearly 3,500 people.

Then, those samples were sent to the University of Chicago’s Argonne National Laboratory for processing and assessment. Each sample’s DNA was amplified and sequenced, then those sequences were used to ID and categorize all the different types of collected bacteria.

Generally, bacterial phone and shoe samples collected from the same person displayed similar, or distinct, bacterial communities. For the most part cell phone samples usually contained bacteria synonymous with people, while shoe samples carried microbes typically found in soil. Also, microbes taken from shoes were almost always more diverse than phone samples. All of these initial findings were fairly straightforward and expected. 

Now, moving on the more unexpected conclusions drawn from the research; despite samples being collected from areas all over the United States, there were no bacterial regional trends discovered. Some people attending the same event in the same place had very similar bacteria on their phones and shoes, but many others had big bacterial differences.

Besides that, the study’s authors were most surprised by all of the microbial dark matter they found on collected samples. They even went so far as to say that a “substantial portion” of the bacteria taken from volunteers is considered pretty much a mystery to modern science.

So, why are these microbes such a mystery? And why are they called “dark matter” in the first place? Such forms of bacteria are very difficult to grow or maintain within a laboratory setting. It’s that characteristic that earned these microbes their dark matter nickname, as they are somewhat comparable to the mysterious dark matter found throughout our universe.

Most of these dark matter microbes weren’t even discovered until the recent development of genetic sequencing technology. Regarding where these elusive forms of bacteria come from, researchers say their origins vary greatly. Some can be traced back to obscure origins, such as a boiling acid spring or underground aquifer, while others have simple origins (soil).

“Perhaps we were naïve, but we did not expect to see such a high relative abundance of bacteria from these microbial dark matter groups on these samples,” comments co-author & Professor Jonathan Eisen of the UC Davis Genome Center.

Many dark matter microbe types were found in over 10% of all samples, and two specific types were even noted in nearly 50% of all collected swabs.

“A remarkable fraction of people are traveling around with representatives from these uncultured groups on commonplace objects,” concludes Coil. 

These findings are fascinating and showcase just how much we still have to learn about the microscopic world all around us. While many may be disturbed by all of the unknown bacteria potentially lurking on their phone and shoes, it’s important to remember that the vast majority of these microbes are harmless. Still, it’s a good idea to make a habit of cleaning one’s phone a few times per week.

The full study can be found here, published in PeerJ.