The Home Microbiome Project was conducted by researchers from the University of Chicago and the U.S. Department of Energy’s Argonne National Laboratory. The study followed 7 families, which included 18 people, 3 dogs and 1 cat, over the course of 6 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.
Samples were also collected from surfaces in the house, including doorknobs, light switches, floors and countertops. Then researchers performed DNA analysis to identify the different species of microbes in each sample. The results were published August 2014 in Science, giving a detailed analysis of the microbes that live in houses and apartments.
“We wanted to know how much people affected the microbial community on a house’s surfaces and on each other,” Gilbert said.
The study revealed that people have a major impact on their microbiome. In fact, when three of the families moved, it took less than a single day for the new house to look just like the old one, when it comes to the microbial profile.
The research also suggests that when a person (and their microbes) leaves a house, the microbial community shifts noticeably in a matter of days.
“You could theoretically predict whether a person has lived in this location, and how recently, with very good accuracy,” Gilbert said.
For members of the same household, the individual’s hands were most likely to share similar microbes; whereas, their nose would have a more unique variation.
Married couples and their young children were shown to share most of their microbial community.
Physical contact between people also mattered. For example, in one home, where two of the three occupants were in a relationship with one another, the couple shared many more microbes. Married couples and their young children were also shown to share most of their microbial community.
Due to the unique nature of a microbial signature, Gilbert suggests home microbiome studies could potentially serve as a forensic tool. Given an unidentified sample from a floor in this study, he said, “we could easily predict which family it came from.”
The researchers also wondered about how pets would change the mix. Gilbert said they found more plant and soil bacteria in houses with indoor-outdoor dogs or cats.
In one case, the researchers also tracked a potentially pathogenic strain of bacteria called Enterobacter, which first appeared on one person’s hands, then the kitchen counter, and then another person’s hands.
“This doesn’t mean that the countertop was definitely the mode of transmission between the two humans, but it’s certainly a smoking gun,” Gilbert said. “It’s also quite possible that we are routinely exposed to harmful bacteria — living on us and in our environment — but it only causes disease when our immune systems are otherwise disrupted.”
The study was funded by the Alfred P. Sloan Foundation. Additional funding also came from the National Institutes of Health, the Environmental Protection Agency, and the National Science Foundation.