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Infant Microbiome Development Traced to Multiple Maternal Transmission Sources

NEW YORK – New research by investigators at the University Medical Center Utrecht, the University of Edinburgh, and elsewhere suggests that mother-to-infant microbiome transmission can occur across numerous body sites, arguing against the notion that babies born by cesarean section lack the maternal microbes found in babies arriving by vaginal birth.

"We saw that many niches of the mother are important for the transmission of microbes, and if some of these pathways are blocked for one reason or another — in this case, we saw that happening with the cesarian section — then these microbes can still reach the infant through other paths," senior and co-corresponding author Wouter de Steenhuijsen Piters, a data scientist affiliated with the University Medical Center Utrecht and the National Institute for Public Health and the Environment's Centre for Infectious Disease Control, said in a statement.

For a paper appearing in Cell Host & Microbe on Wednesday, he and his colleagues used 16S ribosomal RNA gene sequencing to profile microbial community members in 120 women sampled during and after pregnancy, along with samples collected from their infant children at birth and at several time points over their first month of life.

All told, the team considered almost 2,500 samples originating from half a dozen maternal or infant sampling sources — a collection that included nasopharyngeal, skin, vagina, breastmilk, saliva, and fecal samples from mothers, as well as infant nasopharyngeal, skin, saliva, and fecal samples.

"Multiple studies have assessed mother-to-infant transmission of microbes, but they have largely focused on how maternal microbiomes shape the infant gut microbiome," de Steenhuijsen Piters explained in an email, noting that "selection of maternal microbiomes was limited and especially breastmilk has not been studied much in the context of microbial transmission."

The team's analyses suggested that the proportion of infant microbes originating in the mother was comparable in both the vaginal birth and cesarian section baby groups, coming in at an estimated 58.5 percent of infant microbiome communities, on average. But, not surprisingly, the apparent source of those microbes and the specific microbial representatives involved did differ.

"All maternal source communities seed multiple infant niches," the researchers reported, adding that their results pointed to "shared and niche-specific host/environmental factors shaping the infant microbiota."

While infants born vaginally had microbes that coincided with those found in their mothers' vaginal and fecal microbiome sites, for example, the researchers saw an overrepresentation of breastmilk-associated microbes in the babies born by cesarean section.

"[I]n line with previous findings, we found that vaginal delivery is associated with a stronger contribution of vaginal/fecal microbes from mother compared to cesarian delivery," said de Steenhuijsen Piters. "What we did not expect was that this lack of vaginal/fecal microbes in cesarean-borns appears to be (partially) compensated by breastmilk-associated microbes."

Such findings suggest that breast feeding "becomes even more important for children born by cesarean section who do not receive gut and vaginal microbes from their mom," first and co-corresponding author Debby Bogaert, a pediatric immunology and infectious diseases researcher affiliated with the University Medical Center Utrecht's Wilhelmina Children's Hospital and the University of Edinburgh Queen's Medical Research Institute, said in a statement.

"Next, we want to explore whether this early life process, influenced by mom, is affecting not only short-term infection risk in the first year of life but also longer-term health in terms of things like allergies and asthma," Bogaert added, noting that such insights may ultimately inform future disease prevention, diagnosis, and treatment.

The investigators noted that additional research will be needed to explore the sources of infant microbial community contributors that were not explained by mother-to-child transmission in the current analyses.

"It would be interesting to stratify that unknown fraction to see where all the microbes come from; whether fathers contribute, for example, or siblings, or the environment," de Steenhuijsen Piters noted.

More generally, the results indicated that "mother-to-infant transmission of microbes is a very flexible system, which is hopeful," he explained, adding that a more refined view of microbial transmission may also present future opportunities to develop prebiotics or probiotics for infants who are missing certain microbes due to cesarean birth, non-breastmilk feeding, or antibiotic use.