Tracking bacteria at a finer level than species, so a specific lineage in the infant can be matched to the same lineage in the mother. It is measured here because only strain level matching can show that a microbe was actually passed on, rather than picked up separately from the environment.
Drawn from the paper's approach as described.
The authors note that the establishment of the infant gut microbiome is critical for later health, yet how it is shaped by maternal and early life factors remains unclear.
That is why they sampled repeatedly from early pregnancy through the first year, and sequenced the breast milk and vaginal microbiomes alongside the gut, rather than sampling once and inferring the rest.
Drawn from the paper's introduction, which states the open question rather than a formal hypothesis.
The Lifelines NEXT birth cohort followed 714 mother and infant pairs with repeat stool sampling from twelve weeks of pregnancy through one year postpartum, producing 4,526 longitudinal samples. Those were integrated with 474 clinical and exposure variables and with ultra deep sequencing of breast milk and vaginal microbiomes, so the three candidate routes of transmission could be compared against each other rather than assumed.
The maternal gut microbiome itself changed only subtly across pregnancy and postpartum, shifted by diet, infections and pre pregnancy smoking. It was also the main source of the infant's gut strains. Transmission from the vaginal and breast milk microbiomes happened only occasionally. Strain sharing was time dependent, and the more abundant a species was in the mother's gut, the more likely it was to be passed on. The maternal gut microbiome also predicted infant eczema.
Mode of delivery and feeding mode were still the primary shapers of the infant gut microbiome and its functional profiles. But of 585 vaginally delivered infants, 155 were born at home, and home delivery was only moderately associated with infant gut composition, on a par with birth parameters like duration of pushing and ruptured membranes.
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Shown in this study The study measured this step directly.
Because the team matched bacteria at strain level rather than species level, they could show which lineages were actually passed on rather than acquired separately. On that measure the maternal gut is a major reservoir for infant gut strains, and the vaginal and breast milk microbiomes contribute only occasionally.
Sharing is time dependent, and the more abundant a species is in the mother's gut, the more likely it is to be transmitted, which is the dose relationship you would expect if the maternal gut were the source.
Drawn from the paper's results, where strain level matching was the measurement.
It is now more likely that the mother's own gut, rather than the birth canal, supplies most of what colonises an infant's gut. That refines an origin story in which vaginal transmission has carried most of the emphasis, while confirming that delivery mode still matters through some route this study does not isolate.
Mother and infant pairs in a Dutch birth cohort, followed from twelve weeks of pregnancy to twelve months postpartum.
An intervention that deliberately alters the maternal gut microbiome and then follows infant colonisation and health outcomes, which would move this from a map of transmission to a test of it.
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