Can intestinal flora be "transmitted" between people? I love you, so I share my intestinal flora with you!

As the saying goes, "Birds of a feather flock together." The more time you spend together, the more you will be influenced by each other's character and behavior. It is said that two people will become more and more alike after living together for a long time, not only in appearance and the way they behave, but even their intestinal flora will be transmitted to each other and become more and more similar.

In order to understand how intestinal flora is transmitted between people, scientific research teams around the world have launched large-scale sample collection, including skin swabs, feces and saliva, to analyze the composition of the flora. The subjects of the sample collection include mothers and children, couples or family members living together, adult twins, etc. The place of residence of each participant who provided the sample was also recorded in detail, accurate to the village, in order to understand whether the intestinal flora of people within the village or between cities have some common characteristics. This type of research has been carried out in as many as five continents and 20 countries, including the United States, China, Italy, Colombia, Cannes, Tanzania, Argentina, etc. By detecting the types and proportions of strains in the samples, scientists have described the commonalities and individualities of the intestinal flora of people in different countries, villages, and families, and revealed the similarity and transmission characteristics of the intestinal flora between mothers and infants and between family members [1].

The original intestinal flora is a gift from mother

Although we live in a world full of microorganisms, every newborn is almost sterile inside and out when they are born. Our mothers give us 50% of our genes, our first food, and our initial intestinal flora. The intestinal flora that babies first acquire are very diverse and come from the mother's skin, mouth, vagina, intestines, etc. These strains stay in the intestines for a short time and eventually find a more suitable environment for survival, such as on the baby's skin. The bacteria that actually stay in the baby's intestines for a long time include Bacteroides vulgaris, Bifidobacterium longum, and Bifidobacterium breve[2].

The proportion of intestinal flora shared between mother and baby can be as high as 50%, and the similarity of their oral intestinal flora is also very high, exceeding 70% in infants (0-3 years old). As the baby grows, the similarity of the flora decreases, especially after weaning, when the food that the baby can eat becomes more and more abundant, and the diversity of their intestinal flora increases sharply. However, some strains that we get from our mothers when we are still babies can even stay in our intestines for a lifetime. The one with the highest mother-to-child transmission rate is a type of bifidobacterium, which can reach 92% [3].

Close contact provides an opportunity for bacterial exchange

From living under the same roof, in the same village, to living in the same city, as the distance increases, the similarity of the flora gradually decreases. Taking the oral flora as an example, the overlap of oral flora between family members can be as high as 32%, while the overlap of oral flora between people who do not live together is only 3%. The highest similarity between couples or lovers is the skin flora, followed by the oral cavity, and finally the intestinal flora. This is obvious, physical contact and kissing are good opportunities to exchange flora. However, studies on adult twins have found that the similarity of the flora of twins living in different cities is about the same as that of people living in the same village, probably because the twins have obtained highly similar flora from their mothers since childhood.

The picture comes from Tuchong.com

In addition to family members living together, people in the same village also have some commonalities in their microbiota. Even the composition of their intestinal microbiota is closer among people in the same village, which shows that the microbiota can leave the home and spread over long distances, or it may be related to some special eating habits in certain areas.

You also carry your furry child’s bacteria on your body

Since living together for a long time can allow us to share our microbiota, then do pets, one of our most important family members, also share their microbiota with us? The answer is yes. Babies who grow up with cats and dogs will also carry strains unique to small animals. The presence of pets will change the microbial environment in the air or on the surfaces of objects in the home. Babies will acquire strains of small animals when they crawl around or pick up food on the floor, not to mention the strains they directly acquire when they cuddle or kiss their pets. Interestingly, these children who have been exposed to small animals since childhood are less likely to have excessive immune reactions such as allergies during their growth [4]. Perhaps this is because they have been exposed to more immunogens and a richer microbiota since childhood, so their immune systems are accustomed to it.

Not only children, but adults are also easily "infected" by the bacterial flora of pets. For example, the bacterial flora on the skin of adults who keep dogs is more similar to that of their own dogs, and more different from that of other people's dogs[5]. In this way, can we use bacterial flora similarity to prove who is our dog?

Although intestinal flora is different from pathogenic bacteria or viruses, the closer people live and the more frequent their contact, the more similar their flora composition is. Isn't this a kind of "chronic infection"? And whether this type of "infection" is also related to certain diseases is a topic that is worth further study. In particular, some genetic diseases such as diabetes and heart disease, in addition to genetic problems, are they also related to the intestinal flora transmitted between mother and child?

References

1. Valles-Colomer, M., Blanco-Míguez, A., Manghi, P. et al. The person-to-person transmission landscape of the gut and oral microbiomes. Nature 614, 125–135 (2023).

2. Ferretti P, Pasolli E, Tett A, et al. Mother-to-Infant Microbial Transmission from Different Body Sites Shapes the Developing Infant Gut Microbiome. Cell Host Microbe. 2018;24(1):133-145.e5.

3. Browne HP, Shao Y, Lawley TD. Mother-infant transmission of human microbiota. Curr Opin Microbiol. 2022;69:102173. doi:10.1016/j.mib.2022.102173

4. Tun, HM, Konya, T., Takaro, TK et al. Exposure to household furry pets influences the gut microbiota of infants at 3–4 months following various birth scenarios. Microbiome 5, 40 (2017).

5. Song SJ, Lauber C, Costello EK, et al. Cohabiting family members share microbiota with one another and with their dogs. Elife. 2013;2:e00458. Published 2013 Apr 16. doi:10.7554/eLife.00458

This article is a work supported by Science Popularization China Starry Sky Project

Author: Zhao Bei

Reviewer: Wang Xin (Deputy Chief Physician, Department of Oncology, Cancer Hospital, Chinese Academy of Medical Sciences)

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.