Study: Microbiome Is Shaped By Who We Live With, Couples Share More Than They Realize

Key Points:

• A new study reveals that romantic partners share mouth bacteria at significantly higher rates than gut bacteria, likely due to direct contact such as kissing, with couples showing a median oral bacteria sharing rate of 44.4% compared to 19.5% for gut bacteria.
• Researchers analyzed 1,644 paired saliva and stool samples from 808 individuals across 207 households, tracking bacterial strains to determine microbial sharing between people and body sites, finding that mouth bacteria turnover is faster than gut bacteria.
• The gut bacteria most transmissible between housemates tend to be associated with poorer cardiometabolic health, including species enriched in type 2 diabetes, though causation has not been established; some transmissible species also show traits linked to sanitizer resistance and acid-stress survival.
• Strong evidence indicates that mouth bacteria regularly seed the gut, with 74.5% of strain-level matches showing the same bacterial strain in both the mouth and gut of individuals, supporting a two-step transmission process: bacteria spread between people, then move from the mouth to the gut.
• The study underscores that a person’s microbiome is dynamic and influenced by close contacts, highlighting the importance of understanding microbial sharing due to its potential links to health outcomes.