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Scientists: the human microbiome can be contagious!

The community of people living around you can influence the community of microbes living inside you.

And the largest and most diverse review to date has found evidence that who you live with and grow up with may have a greater impact on your microbiome than certain lifestyle factors, age, or even genes.

The study, led by microbiologist Nicola Sigata of the University of Trento in Italy, doesn’t explain how microbes pass directly from one person to another, but instead shows how many gut and mouth bacteria those around us have.

The researchers concluded that social interactions may help shape the human microbial community, which in turn may “play a role in microbiome-related diseases.”

The findings are based on over 9,000 stool and saliva samples collected from participants with known links to each other. These communities were deliberately selected from 20 different countries around the world, not just Western or developing countries.

The results strongly suggest that the trillions of symbiotic cells in our bodies can efficiently spread between human hosts even through brief public encounters.

And the strains of bacteria shared by study participants were found to be “extensive.” In fact, researchers have identified more than 10 million cases of exposure to bacterial strains of mothers and infants, members of the same household or people in communities.

Previous research has shown that a mother helps revitalize her baby’s microbiome in the first few months of life by sharing some of her own bacteria with her, usually through vaginal delivery, breastfeeding, or touch.

It is also known that a person’s microbiome can fluctuate throughout their lifetime depending on what they eat, how much exercise they get, or what environment they live in.

In comparison, person-to-person transmission of the virus has not been widely studied.

As expected, the most important route of transmission was from mother to child. In 711 cases, about 50% of the same bacterial strains were common between mother and child in the first year of life, with 16% of these strains coming from the mother.

In addition, this microbial taxa community can still be found in late adulthood, albeit at lower percentages. For example, at age 30, the average person in the study retained about 14 percent of their mother’s original bacterial strains. Even at age 85, the mother’s most contagious strain was still present in her offspring.

With age, the influence of the maternal germline is balanced by other relationships. And the person they live and interact with on a daily basis has an increasing impact on their microbiome.

For example, after the age of four, the researchers found that the child was equally present with the bacterial strains of the mother and father. What’s more, the longer identical twins stay apart, the fewer microbial strains they have in their gut.

Overall, 12 to 32% of bacterial strains found in the gut and mouth are shared with other strains. Such lifestyle factors were not enough to explain the results.

When the researchers switched to larger populations, they saw a similar but smaller relationship.

It appears that less than a percent of bacterial strains jump between households in the same rural community, making this type of transmission relatively rare. However, the transmissibility of bacterial species by rural communities was very consistent across all datasets.

In about 67% of the communities studied, people from the same village but from different households had more common bacterial strains than did households in other villages.

The findings suggest that even superficial interactions can affect the human microbiome, for better or worse. While some microbes can provide health benefits, others can disrupt the microbiome, leaving people vulnerable to disease.

The study was published in the journal Nature.

Source: Science Alert


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