Infant gut microbiota contribute to an array of benefits for their human hosts; digestion, vitamin production, homeostasis, immunity and the list goes on. The microbiome is first established shortly after birth, and the mode of delivery can shape colonization and dynamics of a newborn’s gut community.
A recent article from BBC highlights gut microbiome differences between vaginally and Cesarean-section (C-section)-delivered Scottish and Dutch infants. According to the article, vaginally delivered infants raised double the amount of antibodies in response to childhood vaccines than those born by C-section. This suggests that exposure to maternal vaginal microbiota during birth may enhance immune system development, leading to improved vaccine responses in early childhood.
This article will explore some basics of the infant gut microbiome and its composition, before taking a closer look at research into how mode of delivery affects and infant microbial colonization.
Understanding Infant Gut Microbiota Composition
To understand the infant gut microbiome, scientists have looked at the variety of bacteria present in infants’ digestive systems over the first three years of life. Using a large set of genetic data (from over 10,000 samples), they identified eight main types of bacterial communities, known as Infant Community State Types (ICSTs).
These ICSTs vary depending on factors like location and the child’s health. By analyzing how different bacterial strains coexist and interact, researchers could track how these bacteria affect early development, digestive health, and immunity in infants, helping create a healthy gut microbiome for more young children.
Additional research suggests that infant gut microbiota composition is influenced by several perinatal and postnatal factors, including:
- Mode of delivery
- Feeding type
- Antibiotic exposure
- Post-weaning diet
- Host genetics
Which Bacterial Species Are Beneficial To the Infant Gut?
Beneficial bacteria for developing an infant’s gut microbiome include Bifidobacterium infantis (B. longum subsp. infantis) and Bifidobacterium breve. These bacteria aid in establishing other helpful intestinal microbiota. B. infantis, in particular, is well-suited to thrive in an infant’s gut due to its genetic adaptation to utilize nutrients in breast milk fully, making it a key player in early gut health.
What are the Stages of Infant Gut Microbiome Development?
Infant gut microbiome development generally occurs in three key stages. According to the TEDDY study, which analyzed stool samples from infants over 43 months, these stages are the developmental phase (3–14 months), when initial bacterial colonization begins; the transitional phase (15–30 months), with rapid changes due to dietary shifts like introducing solids; and the stable phase (31–46 months), where the microbiome reaches a mature, stable state.
These phases are influenced by factors like environment, maternal microbiota, and early life exposures, which may impact immune development and even disease risk.
How Does Mode of Delivery Alter Infant Gut Microbiome Development?
According to the studies, differences in beneficial commensal bacteria mediate the immune response to vaccines, with vaginal delivery enriching for more commensal bacteria in infants.
Vaginally delivered infants are first introduced to the microbes in their mothers’ genitals, which include commensal stool organisms and lactic acid-producing lactobacilli. Conversely, C-section newborns are introduced to microbes on the skin or in the hospital or home. These microbes typically include members of the Staphylococcus and Cutibacterium genera, which are generally not commensal gut organisms and may not be as beneficial to the developing gut microbiome and immune system.
The differences in microbial colonizers of vaginally and C-section-delivered newborns and the implications this could hold for immune system development has led to studies investigating gut microbiome variation and its role in immunity in infants. A common focus of those studies is immune response variation in newborns.
In a study from the University of Edinburgh, Spaarne Hospital and Utrecht University Medical Centre, researchers examined gut microbiome variation in newborns. They collected the first fecal sample of life, called meconium, from 120 newborns. Then they sequenced the 16S rRNA gene in all samples to profile the bacterial composition at the species level. Whole genome shotgun sequencing was also performed on a subset of meconium samples to validate the microbiome findings of the 16S rRNA profiling.
The findings from the study illustrated higher levels of Bifidobacterium and Escherichia coli species associated with anti-pneumococcal antibody response in vaginally delivered newborns. This suggests an important role of these taxa in heightening vaccine responses, and that vaginal delivery may be important to their establishment.
On this point, Professor Debby Bogaert, the chair of pediatric medicine at the University of Edinburgh, highlights the importance of the first interaction between the host immune system and microbes. According to her, the release of short chain fatty acids (SCFAs) by gut bacteria marks the activation time of the newborn immune system. When SCFA production is lacking, there are fewer B-cells to produce antibodies.
Practical Applications Of This Research
Due to the lack of transfer of beneficial commensal microbes following a C-section delivery, the use of some type of seeding mechanism has been proposed.
To replace the missing microbiome, studies have attempted to seed cesarean delivered newborns with the vaginal and gut microbes of their mothers. Yet, Prof. Bogaert approaches these attempts with caution, emphasizing that, in practice, safely transplanting microbes to infants may be complicated and even dangerous.
The risks would be confounded when considering the high number of babies born by C-section. To overcome these risks, Prof Bogaert suggests that giving a precise bacterial supplement may do the trick. These are recent findings from a relatively small study, but may be paving the way for a future where microbes could be manipulated to improve the immune systems of C-section-delivered babies.
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Infant Gut Microbiome FAQs
Are babies born with a gut microbiome?
No, babies are generally not thought to be born with a colonized gut microbiome. They begin developing during birth, starting with exposure to neonatal gut microbiota from their mother and environment after leaving the womb, as the environment in-utero is usually sterile and bacteria-free. However, some studies have shown evidence of prenatal colonization of bacteria in some cases of preterm birth, meaning that in some cases gut microbes can also begin to develop in-utero.
What are the three stages of infant microbiome development?
Research into the evolution of the gut microbiome shows three distinct stages in infant microbiome development. These are a developmental phase (months 3–14), a transitional phase (months 15–30), and a stable phase (months 31–46).
How long does it take for babies to develop a full microbiome?
It typically takes around two to three years for babies’ gut microbiota development to reach a mature or stable phase.
