Do Cesarean-Section Babies Still Receive Essential Microbes?

Of the many things mothers give their infants, microbiota seeding is among the earliest and most crucial to future health.

The human microbiome is essential for nutrient utilization, colonization resistance, and immune system education and development. Early disturbance of the microbiome may increase the risk of developing diseases later in life.

Maternal inheritance is vastly different in babies born vaginally than by cesarean-section. Thus, the question has been raised whether cesarean-section (CS) babies miss out on this mother-to-infant transmission of microbes.

A new study, published in Cell Host & Microbe, assessed mother-to-infant microbiota seeding and early life microbiota development over the first 30 days of life. “We wanted to have a better idea of how the infant microbiome develops in different parts of their bodies and how it’s influenced by factors such as birth mode, antibiotic use, and lack of breastfeeding,” said study author Wouter de Steenhuijsen Piters, a physician and data scientist at the University Medical Center Utrecht in the Netherlands.

de Steenhuijsen Piters and fellow investigators studied mother-infant transmission pathways and early-life development of microbiota in CS- and vaginally born infants. They examined bacterial communities by characterizing and sampling 6 maternal niches (vagina, nasopharynx, saliva, feces, skin, and breastmilk) and 4 infant niches (nasopharynx, saliva, feces, and skin) at 5 time points over infants’ first month of life.

The investigators collected and analyzed a total of 2453 samples from 120 mother-infant pairs. They observed higher diversity in maternal samples, in comparison to infant samples, across all niches and all points in time.

By collecting mothers’ microbiome samples, the investigators sought to determine which of these sources were “seeding” the infants’ biomes. Babies are generally considered to be sterile before birth, thus heightening the importance of vertical mother-to-infant transmission of microbiota.

The investigators determined that 58.5% of an infant’s microbiome is derived from the mother, regardless of birth route. However, different maternal niches contributed to different niches of the infants’ microbiomes. CS-born babies received fewer microbes from their mother’s vaginal and fecal microbiomes, but this was compensated by receiving more microbes from breastmilk.

“Microbiome transfer and development are so important that evolution has ensured that those microbes are transferred one or another way from mother to child,” said Debby Bogaert, the first author of the study. “Breastfeeding becomes even more important for children born by cesarean section who do not receive gut and vaginal microbes from their mom.”

Diversity across the 4 infant niches exhibited 2 distinct patterns over time. The first was a gradual increase in microbial diversity over the first month of life (feces), and the second was a high initial diversity, followed by rapid selection during the first few days of life, after which diversity increased again (nasopharynx, saliva, and skin microbiota).

In follow-up research, the investigators want to study how microbiome development relates to long-term health. Additionally, they are planning to examine nonmaternal influences on infant microbiome development.

“We could see that the maternal microbiome explains almost 60% of the infant’s total microbiome, but there’s still 40% that we don't know about,” de Steenhuijsen Piters said. “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.”