TRENTO — Cohabitating romantic partners share approximately 44 percent of their oral microbiome and 19 percent of their gut microbiome, according to a study published in Cell Press. This microbial sharing is attributed to transmission through close contact, such as kissing, and shared living environments.

Researchers analyzed microbiome DNA data from 430 individuals across 207 households in Italy and Fiji to quantify microbial transmission rates. The study found that individuals living in the same household share about 26 percent of their oral microbiome, irrespective of their specific relationship. Computational Biologist Vitor Heidrich said, "When people exchange saliva directly, such as through kissing, you indeed see much more strain sharing."

Heidrich said, "It is difficult to grasp the idea that we are sharing gut microbes, because this entails that we are, to some extent, swallowing fecal matter from our housemates." He added, "Even a single microbial cell can be enough for a successful transmission event." Researchers observed that some transmissible microbial species are linked with a higher risk of Type 2 diabetes.

Infectious Disease Doctor Jessica Queen said, "We have trillions of bacteria in our gut, and really trying to experimentally prove what is causative versus correlative, and what's the sequence of events, is actually very difficult." Heidrich said, "Unless my strains physically travel from me to you, the same diet alone will not necessarily make us share more of our strains." He added, "People living in different households but from the same community, like the same town, do share more strains than people from completely different populations."

Microbiome Researcher Nicola Segata said, "This speaks to the fact that most of our microbes are kind of everywhere, and the microbial exchange is very high." Heidrich said, "If we can identify the characteristics that make some microbes more transmissible than others, and the constraints that make beneficial microbes less transmissible, we can apply that to make fecal microbiota transplants much more effective." He noted, "Humans and our primate relatives have always lived in groups, so this kind of microbial exchange has likely been happening for millions of years, shaping the evolution of our microbiomes." Heidrich added, "It is a mechanism intrinsic to the condition of being human and that we should not be afraid of."