TOPLINE

People with close family ties who lived together shared more oral and gut microbes with each other than with other people in their communities.

METHODOLOGY

• Researchers analyzed 1644 paired oral and fecal metagenomes from 808 individuals in 207 households in Italy and Fiji to map microbiome strain transmission patterns across household and body sites.
• They used strain-level phylogenetic analysis to identify shared microbial strains between individuals with close family ties who were living together and compared strain-sharing rates across different household relationship types (eg, siblings or partners).
• Additional analyses examined the transmissibility of individual microbial species and their associations with cardiometabolic and cancer biomarkers.

TAKEAWAY

• Cohabitants shared significantly more oral and gut strains than people from the same population who did not live together; on average, cohabiting individuals shared 19% of their gut microbiome strains and 25.8% of their oral microbiome strains compared with 6% and 0%, respectively, for individuals living in different households.
• Romantic partners shared more oral (but not gut) microbes with each other — a median of 44.4%, likely due to kissing.
• Highly transmissible gut species were mainly associated with biomarkers for type 2 diabetes and poorer cardiometabolic health, whereas in the oral cavity, the most transmissible species included two microbes associated with colorectal cancer and several opportunistic pathogens.
• A within-individual analysis found that oral microbiome species detected in the gut appeared to originate from the oral cavity via saliva-mediated transmission, with 74.5% of cases involving the same strain in both body sites.

IN PRACTICE

“Understanding natural microbiome transmission can inform more targeted artificial transmission solutions,” said the first author of the study in a press release. “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.”

SOURCE

The study was led by Vitor Heidrich, University of Trento, Trento, Italy, and published online in Cell Press Blue.

LIMITATIONS

The study had limitations. The analysis focused on healthy individuals, so findings may not apply to dysbiotic or disease states where oral-to-gut transmission may be elevated. Strain-level analysis could only be performed on the most abundant strains in each sample, potentially missing subdominant strain transmission. The study included a substantial proportion of mother-offspring pairs, making it difficult to distinguish early-life vertical transmission from horizontal household transmission in some cases.

DISCLOSURES

The study was supported by funding from the European Research Council, NextGenerationEU, the Italian Ministry of Health, the Associazione Italiana per la Ricerca sul Cancro, and the Italian Ministry of Research. The authors declared having no competing interests.

Marilynn Larkin, MA, is an award-winning medical writer and editor whose work has appeared in numerous publications, including Medscape Medical News and its sister publication MDedge, The Lancet (where she was a contributing editor), and Reuters Health.