Human beings, like many life forms, essentially live in an invisible sea of bacteria that follow us wherever we go.

Now scientists want you to know, your unique population of bacteria colonizes your home with you. New research has found that when you move into a new home, your family’s unique population of bacteria launches a complete take-over of the house, wiping out and replacing the bacteria that used to live there. When we move into a new place, we populate it with more new residents: millions and millions of bacteria.

A study published last week in Science provides a detailed analysis of the microbes that live in houses and apartments. The study, conducted by researchers from the U.S. Department of Energy’s Argonne National Laboratory and the University of Chicago, examined the complex interaction between humans and the microbes that live on and around us. A growing body of research provides evidence that these microscopic, teeming communities play an important role in human health, disease treatment, and transmission.

“We know that certain bacteria can make it easier for mice to put on weight, for example, and that others influence brain development in young mice,” said Argonne microbiologist Jack Gilbert, who led the study. “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.

“They are essential for us to understand our health in the 21st century,” he said.

The Home Microbiome Project followed seven families, which included eighteen people, three dogs and one cat, over the course of six weeks. The participants in the study swabbed their hands, feet and noses daily to collect a sample of the microbial populations living in and on them. They also sampled surfaces in common areas used by family members, such as doorknobs, light switches, floors and bathroom, kitchen counter tops.

The families sent the samples to Argonne, where researchers performed DNA analysis to characterize the different species of microbes in each sample. “We wanted to know how much people affected the microbial community on a house’s surfaces and on each other,” Gilbert said.

Researchers found that people substantially affected the microbial communities in a house when moving in. When three of the families moved, it took less than a day for the new house to look just like the old one, in terms of microbial make-up and bacteria species.

Couples that were more touchy-feely also shared many more microbes. Married couples and their young children tended to share most of their microbial community.  (Which is pretty much no surprise to anyone in a family that shared their colds, flus, and other benefits of close quarters.) Adding pets changed the makeup of organisms as well, Gilbert said.