Some of the microorganisms that make up the human microbiome are widely transmitted between individuals through social interaction, according to an international study with the participation of CSIC researchers. Thus, the people with whom we are in close contact constitute a crucial source of bacteria that contribute to human health. The finding may help to understand how microbial species associated with the risk of cardiovascular disease, diabetes, cancer and other diseases are acquired. The study, led by the University of Trento (Italy), is published today in Nature.
The human microbiome, the set of microorganisms that live in the human body, is a great ally of our health. It plays a fundamental role in the functioning of the immune and digestive systems, among many others. However, there is still very limited knowledge about how the bacteria and other organisms that make up the microbiome are acquired and transmitted between individuals.
The research group led by Nicola Segata, from the Department of Cellular, Computational and Integrative Biology (CIBIO) of the University of Trento and the European Institute of Oncology (both in Italy), has coordinated an international study on the acquisition of bacteria associated with health that tries to shed light on this subject. Eighteen institutions and research centers from around the world, including a research group from the Institute of Agrochemistry and Food Technology (IATA-CSIC) led by María Carmen Collado, participated in the study.
According to its authors, this is the largest and most diverse study to date on the transmission of the human microbiome. They investigated how the bacteria are passed between generations (vertical transmission) and between people who live in close contact with each other as partners, children or friends (horizontal transmission). They analyzed more than 9,000 stool and saliva samples from participants in 20 countries and all continents.
The study confirmed for the first time that the first transmission of the gut microbiome occurs at birth and is very long-lasting. In fact, bacteria from the maternal microbiome can still be detected in older people. However, infants lack many of the bacterial species that are common in adults, so the authors hypothesized the pathways of acquisition of these species during life. The analysis showed that adults acquire bacteria through social, person-to-person interactions.
Social interaction modulates the human microbiome
The researchers also found that the oral microbiome is transmitted in a markedly different way from the gut microbiome. In fact, bacteria present in saliva are transmitted more frequently, and mainly through horizontal transmission. Mother-to-child oral microbiome transmission is low, but the more time people spend together, the more bacteria they share.
Mireia Valles-Colomer, a postdoctoral researcher at the Segata Laboratory of the University of Trento and first author of the paper, which traced the transmission of more than 800 species of bacteria, states: “We have found evidence of a wide interchange of the intestinal and oral microbiome related to with the type of relationship and lifestyle. The results suggest that social interactions shape the composition of our microbiomes. We have also found that certain bacteria, especially those that survive best outside of our bodies, are transmitted much more frequently than others. Some of these are microbes that we know very little about, they don’t even have names. This leads us to study them better, as we still have many unanswered questions about the transmission mechanisms of the microbiome and how this affects our health.”
“In adulthood, the sources of our microbiomes are mainly the people with whom we are in close contact,” explains Nicola Segata. “The duration of interactions in students or couples sharing an apartment, for example, is roughly proportional to the number of bacteria exchanged. In many cases, however, the bacteria can spread even between individuals who have casual and superficial interactions.”
Impact of the finding on disease risk
“The transmission of the microbiome has important implications for our health,” continues Segata, “since some non-communicable diseases such as cardiovascular diseases, diabetes or cancer are partially related to alterations in the microbiome. The demonstration that the human microbiome is transmissible could suggest that some of these diseases considered non-communicable could, at least to some extent, be transmissible. Therefore, further studies on the transmission of the microbiome can advance the understanding of the risk factors of these diseases and, in the future, explore the possibility of reducing the risk with therapies that act on the microbiome or its transmissible components.” the investigator advances.
The IATA-CSIC group led by María Carmen Collado is the only Spanish participant in the study. Specifically, the researchers from the Valencian center of excellence collaborated in the analysis of the transmission of the mother-child microbiome, in addition to incorporating samples and data from collaborators in Colombia, Argentina and China, in order to study the vertical transmission and stability of the composition of the microbiome over time in diverse populations geographically located in different places.
For María Carmen Collado, “this study opens new perspectives on how we acquire the microbiome throughout our lives and the fundamental role of social interactions that until now had not been taken into account. How we live and how we relate to our family, friends, and co-workers influences our microbiome. In addition, this study has allowed greater precision in the study of maternal-infant intestinal bacteria transmission, which is very relevant at the beginning of life, lasts over time and can be recognized in the elderly”.
“These multicenter and multidisciplinary studies are necessary to advance knowledge of the acquisition, persistence, and modulation of the human microbiome and its potential effects on human health,” emphasizes Collado. His group has extensive experience in the field, with previous studies on the transmission of the microbiome between mother and child and the factors that modulate this transmission, as well as the consequences derived from covid-19 in breastfeeding, among other recent works.
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