How family, friends, and even neighbors influence our microbiome

People who live in the same home share more than simply a roof (and product from the fridge). Housemates, whether relatives or flatmates, have the same bacteria inhabiting their bodies, and the longer they live together, the more similar their microbiomes get.

The result, based on a study of thousands of people's gut and mouth microbiomes published in Nature, presents the prospect that disorders connected to microbiome malfunction, such as cancer, diabetes, and obesity, might be partially transmissible. According to Katherine Xue, a microbiome researcher at Stanford University in California, this is the most complete research so far on when and why microorganisms transfer into the gut and oral microbiomes. Throughout our lifetimes, new microorganisms can continue to change our microbiomes.

The majority of research on how humans obtain their microbiomes has focused on people's initial interaction with microbes: their mothers. Hilary Browne, a microbiologist at the Wellcome Sanger Institute in Hinxton, UK, explains that it's critical for giving a microbial beginner package.

A team led by microbiome experts Mireia Valles-Colomer and Nicola Segata at the University of Trento, Italy, examined DNA from roughly 10,000 feces and saliva samples from individuals all over the world, from rural settlements in Argentina to a metropolis in China to populations in Europe and North America. The researchers next examined similarities in the microbial strains discovered in the stomachs and mouths of family members, spouses, housemates, and other social interactions.

The study revealed a substantial association between mothers' microbiomes and those of their offspring, especially early in life. Half of the microbial strains in an infant's gut were shared with their moms throughout their first year of life. The level of overlap reduced, but did not disappear, as children matured. Older adults, aged 50 to 85, still shared gut microbial strains with their moms.

Other members of the family were also a significant source of gut bacteria. After the age of four, children shared the same number of microorganism strains with their father. And the longer twins lived apart from each other, the less intestinal microorganisms they shared. Sharing occurred even between homes in many of the rural-living groups: participants from distinct families in the same village had higher gut microbial overlap than those from different villages.

The maternal microbial starting kit has a lower influence on microorganisms in people's lips than it does on those in their stomachs. The researchers discovered that people who lived together tended to have the same microbe strains in their mouths, regardless of their relationship, and the longer they lived together, the more they shared. Couples, on the other hand, shared strains to a larger extent than children and parents.

The researchers also discovered that people from Westernized civilizations shared just as much as those from other cultures. That realization astonished Ilana Brito, a microbiome researcher at Cornell University in Ithaca, New York. She predicted that microbiome transmission would be more difficult to detect in Western societies due to variables such as improved public-health infrastructure that might inhibit spread.

The publication establishes a foundation for further research into how the proliferation of bacteria that aren't considered pathogens might contribute to disease. This will necessitate long-term studies relating individual microorganisms — and their proliferation — to people's health, a route that microbiome research is currently taking, according to Browne. They'll be able to address some of those concerns.