As you move through your house, you leave behind a measurable, microbial "fingerprint."
Researchers made that discovery in a recent study called the Home Microbiome Project.
The project was led by Jack Gilbert, who heads the microbial ecology group at the Argonne National Laboratory and is also an associate professor at the University of Chicago.
His team followed seven healthy families and looked at the microbial map of their homes to find out how bacteria travelled between humans, surfaces and pets. The goal was to figure out how the bacteria move and in which direction, and how that affects the overall microbiome of the house — all the beneficial and pathogenic bacteria that make up the surrounding environment.
The researchers recently published their results in the journal Science.
Gilbert and his team also discovered they could track when someone went away by identifying how the local microbiome changed.
"If somebody left the home, their microbiome signature started to decay very slowly," Gilbert explained. "We could still detect that they used to be in the home, but after about 72 hours it looked like their microbiome signature disappeared. It had been taken over by the other occupants in the house.”
The research also extends outside the confines or the home, into other areas people inhabit, like hotel rooms. Studies trumpeting the most bacteria-laden surfaces in a hotel room are common and have some wary travellers reaching for antibacterial spray or removing comforters from the beds after checking in. Gilbert said he doesn’t do any of those things when he travels.
"If you go into a hotel room, your microbiome takes over that hotel room in under three hours," he said. "Toilet, bed, floor — everything, starts to look like the microbiome of your home and your microbiome, particularly. Within two to three hours you’ve eradicated the previous [guest's] microbiome.”
Gilbert says viruses are a different story, but in order for bacteria to make you sick, all the elements have to align in a perfect storm.
“The likelihood that somebody in that hotel room left a severely nasty pathogen in there and that you are susceptible to picking up that nasty pathogen is infinitesimally remote," Gilbert said.
"And so it’s very hard for a microbiologist to listen to those anecdotal stories and not get a little bit cringey."
Gilbert says most bacteria have no influence on your health.
Real estate for bacteria
On the other hand, some bacteria in and around us do affect our developmental physiology and may have an impact on our behaviour and neurological development, but in a good way.
Citing an example, Gilbert pointed to a recent study by his colleague Cathryn Nagler, that identified a type of bacteria that protects mice from an allergy to peanuts.
Having a diverse microbiome appears to be healthy.
"Think of yourself as real estate," he explained. "And if the bacteria that populate your body are depleted then there’s lots of spare real estate available."
If that happens and you come into contact with a known pathogen, the pathogen will take up that available real estate, Gilbert said.
"But if you’ve got a rich rainforest full of bacteria living inside and on you, [and] don’t have any spare real estate, it [the pathogen] can’t settle on you and it can’t propagate and you won’t get sick.”
Gilbert and his team have now moved on to a new study called the Hospital Microbiome Project. They had noticed that pathogenic bacteria found in the home study didn’t make occupants sick. Now they want to figure out why those same bacteria can become a problem for people with depressed immune systems in the hospital.
In the meantime, Gilbert says there are easy ways to increase your chances of having a rich, healthy microbial environment in your house — by opening windows, adding houseplants and getting a pet.
“We bought a dog because of the Home Microbiome Project," Gilbert said. "The evidence from that was that dogs are really helpful at increasing that microbial transmission. They rapidly increase the types of bacteria and the amount of bacteria that move between us and our surfaces, us and our other occupants.”
Essentially, the research is uncovering "the mechanisms behind everything your mother ever told you to do" to stay healthy, from getting some fresh air to eating a proper meal, Gilbert said.
"My mother was right — that’s what we should be doing. But we now have evidence-based reason why we should be doing that.”