A detailed analysis of the microbes that live in houses and apartments shed light on the complicated interaction between humans and the microbes that live on and around us / Argonne National Laboratory

Home is where the microbes are, millions and millions of microbes. Every single household has a different microbial community, and every time we pack up our stuff and move someplace else, our microbiological auras move too, according to a study published in Science this week. These microbes can populate new homes within just a single day.

“We know that certain bacteria can make it easier for mice to put on weight, for example, and that others influence brain development,” says Jack Gilbert at Argonne National Laboratory in a news release. “We want to know where these bacteria come from, and as people spend more and more time indoors, we wanted to map out the microbes that live in our homes and the likelihood that they will settle on us.”

Gilbert and colleagues from the Home Microbiome Project studied seven families—that’s 18 people, three dogs, and one cat—and their homes over the course of six weeks. The researchers collected daily swabs and sequenced the genomes of bacteria colonizing the skin of each family member, pet, and household surface—from doorknobs and light switches to countertops and floors.

The researchers identified 4 million DNA sequences and 21,997 distinct genomes (or operational taxonomic units, OTUs) from 1,586 different samples. Not surprisingly, the microbial communities on hands, feet, and noses reflected those on the home surfaces: Doorknobs looked like hands and floors looked like feet, microbially speaking. Homes with indoor-outdoor dogs or cats had more plant and soil bacteria.

By tracking the transfer of OTUs, the team found that people act as sources of bacteria more often than household surfaces. In one case, the potentially pathogenic Enterobacter first appeared on a person’s hands, then the kitchen counter, and then another person’s hand.

And it all happens fast. When someone leaves the house for a few days, that person’s aura quickly diminishes. And when three of the families moved to a different house or apartment—including one family that moved from a hotel room to a house—it took less than a day for the microbial signature of the new abode to look just like that of the old digs.

“People always say, ‘Ewwwww, someone else was in this room and it has their microbes all over it.’ That’s irrelevant,” Gilbert tells National Geographic. “You are constantly overwriting the microbes in the world around you with your own.”

Compared to other people, those living in the same home have more microbes in common with each other: Roommates share some, couples share more, and parents with young children share the most. However, individuals do have somewhat unique microbial signatures, no matter where we move, inside our noses.

Home microbiome signatures might one day be used as a forensic tool to catch criminals. Given an unidentified sample from a floor in this study, “we could easily predict which family it came from,” Gilbert says. And theoretically, he tells New Scientist, the technique could detect a new relationship or uncover a cheating partner.

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