Finding the Source of Gut Microbiome Transmissions

The personal genetic makeup of the microbiome can be influenced by long-lasting close contact, according to a paper published in Nature.

Investigators from Italy conducted an integrative multi-cohort study of microbiome transmission in order to previously overlooked person-to-person transmission types. They ultimately used 9715 samples from 31 human metagenomic datasets, which included transmission between healthy mothers and offspring, households, twin pairs, villages and populations (defined by westernized vs. non-westernized, as well as other demographics related to diet). The study authors said these datasets, with a combination of saliva and stool samples, came from 20 countries in the Americas, Africa, Asia, and Europe. The investigators examined samples from at least 15 healthy individuals to whom no intervention was performed, who had at least 2 samples taken 6 months apart.

The investigators determined that mother-to-infant gut microbiome transmission was what they called “considerable and stable” during infancy, with about 50 percent of the same strains among shared species. This relationship remained detectable until approximately age 3 years, they noted. Additionally, 16 percent of the strains detected in the infants originated from the mother with only slight reductions after the first few days, the study authors said. For example, they wrote that at 1 day, 1 week and 1 year, respectively, the strain-sharing rates were 65, 50, and 47 percent.

The investigators learned that vaginally-delivered infants up to 1 year of age had significantly higher strain-sharing rates with their mothers compared to other delivery methods. However, by 3 years of age, there were no differences detected among the different delivery methods.

The study authors further observed that transmission of the oral microbiome happened largely horizontally and was enhanced by the duration of cohabitation, they wrote, with between 12 to 32 percent median strain-sharing rates for the gut and oral microbiomes. The study authors added that time since cohabitation, more than age or genetics, contributed to strain sharing.

Oral strain-sharing rates increased with offspring age for kinship-associated patterns, especially after the age of 3 years, the study authors found. Strain-sharing rates were slightly higher between mothers (30 percent) and their infants compared to fathers (24 percent), which the study authors attributed to greater intimacy, such as through breastfeeding.

Maternal and paternal strain-sharing rates were similar in children aged 4 and older, the study authors found. They also wrote that there was slightly higher strain sharing that occurred between younger, ie, less richly colonized, genetically related siblings than between partners. To account for later-in-life cohabitation, the study authors looked at sets of twins. They determined that strain sharing among adult twins might result from past cohabitation rather than long-lasting effects of shared transmission from their parents.

“The transfer of microorganism strains among individuals in long-lasting close contact is a major driver in shaping the personal genetic makeup of the microbiome, and thus of the corresponding metabolic and host-microorganism interaction potential,” the study authors concluded. “Our results reinforce the hypothesis that several diseases and conditions that are currently considered non-communicable should be re-evaluated, and that accounting for transmissibility and social network structure will improve the design of future microbiome investigations and modulation approaches.”