SAN FRANCISCO — You may be bringing home a few new friends the next time you take a swim in the ocean. Researchers at the University of California have found that ocean bacteria invade and change the skin microbiome after just 10 minutes of swimming, increasing the likelihood of infections.
Our skin is naturally home to millions of bacteria and fungi, and while this may sound a bit unnerving at first, these little stow aways actually help regulate our immune systems and protect us from unwanted pathogens and infections. This community of organisms is referred to as the skin microbiome by the scientific community.
“Our data demonstrates for the first time that ocean water exposure can alter the diversity and composition of the human skin microbiome,” explains lead author Marisa Chattman Nielsen, in a release. “While swimming normal resident bacteria were washed off while ocean bacteria were deposited onto the skin.”
This accumulation of ocean bacteria and subsequent change in the skin microbiome can leave swimmers more susceptible to infections and worsen disease states. Examples include ear and skin infections, and gastrointestinal or respiratory illnesses.
The study’s authors say the research was commissioned due to previous studies that have already found a link between ocean swimming and infections, as well as the unfortunate fact that more and more beaches are displaying poor water quality due to waste and storm runoff.
Volunteers for this study had to meet a strict criteria of no sunscreen use, no bathing within the last 12 hours, rare exposure to ocean water, and no use of antibiotics in six months.
In all, nine swimmers were selected for the study. Each swimmers’ calf was swabbed four times; once before entering the water, again after drying off following a 10 minute swim, and again at six and 24 hours post swim.
Each swimmers’ microbiome changed dramatically following a 10 minute swim. Furthermore, all of the swimmers’ post-swim microbiomes were very similar to each other, indicating every single volunteer’s microbiome was indeed colonized by ocean bacteria. Over the course of the next 24 hours, the swimmers’ microbiomes almost completely reverted back to their original compositions. Ocean bacteria was only present on one volunteer after a full 24 hours.
Perhaps even more troubling, some of the bacteria detected on the swimmers’ skin was more than 10 times greater than the fraction detected in actual ocean water samples. This suggests that at least some ocean bacteria has an affinity for human skin.
This study was presented at the 2019 American Society for Microbiology meeting.