Shared home, shared microbiome? Study says flatmates swap gut bacteria

You may share more than the kitchen with your flatmates: people who live together share parts of their oral and gut microbiome, according to a new study by the University of Trento in Italy. Researchers found that cohabiting people share certain microbes regardless of the ‘proximity’ of their relationship. Siblings, parents and children all shared similar numbers of microbial strains. Your flatmates may be living rent-free in your gut, too. Romantic partners, however, shared more oral microbes, which the researchers attribute to kissing. “Who we decide to share our homes with can have a huge influence on our microbiomes, which has potential consequences for our health,” said Vitor Heidrich of the University of Trento, Italy, first author and computational biologist at the University of Trento, Italy. The team analysed 1,644 paired mouth and stool samples to see how microbes spread between healthy people living together, and how microbes move from the mouth to the gut within the same person. People living together shared 19% of their gut microbiome strains and 26% of their oral microbiome strains, compared to 6% and 0% among people who did not live together. Romantic partners shared an average of 44% of their oral microbes. The human gut and oral microbiome are made up of millions of microscopic organisms, including bacteria, viruses, fungi and parasites. They are unique for each person and are determined by a combination of factors, such as birth environment, infant feeding, long-term diet and lifestyle. The exchange is likely to happen through daily contact and shared environments. People living together prepare and eat food together and share bathrooms, which provides opportunities for microbes to move from one person to another. “We know that diet and other lifestyle factors can change our microbiome, but these factors are acting on the microbes that are already within us,” said senior author and computational biologist Nicola Segata of the University of Trento, Italy. “It doesn’t solve the question about where the microbes are coming from.” Segata added that it was surprising that the oral microbiome was only slightly more transmissible than the gut microbiome. “This speaks to the fact that most of our microbes are kind of everywhere, and the microbial exchange is very high, but our microbiomes are shaped more at the level of whether our body accepts the colonisation of these bacteria.” The researchers also found that the microbes most easily transmitted between people were more likely associated with poor health, particularly type 2 diabetes and more generally, poor cardiometabolic health. In the mouth, the most transmissible species included two microbes that are associated with colorectal cancer and several opportunistic pathogens that can cause serious illness in people with weakened immune systems. The authors said that these findings may suggest that disease-associated microbes may possess characteristics that allow them to spread more easily or encounter less resistance when colonising new hosts. “It’s difficult to speculate why this is, but it might be a reflection of their ability to withstand stress,” says Heidrich. “The same traits that help them survive the journey between humans may also allow them to thrive in the inflammatory conditions associated with disease.” The findings could help improve microbiome-based treatments, including probiotic and fecal microbiota transplant therapies, the researchers say.