Infants born by cesarean section have a relatively meager array of bacteria in the gut. But by the age of three to five years they are broadly in line with their peers. This is shown by a study that also shows that it takes a remarkably long time for the mature intestinal microbiota to get established.

Fredrik Backhed, Professor of Molecular Medicine at Sahlgrenska Academy, University of Gothenburg, has been heading this research. The study, conducted in collaboration with Halland County Hospital in Halmstad, is now published in the journal Cell Host & Microbe.

Professor Backhed and his group have previously demonstrated that the composition of children’s intestinal microbiota is affected by their mode of delivery and diet. In the current study, the researchers examined in detail how the composition of intestinal bacteria in 471 children born at the hospital in Halmstad had developed.

The first fecal sample was collected when each child was a newborn infant. Thereafter, sampling took place at 4 months, 12 months, 3 years and 5 years. The scientists were thus able to follow the successive incorporation of various bacteria into the children’s gut microbiota.

At birth, the infant’s intestine has already been colonized by bacteria and other microorganisms. During the first few years of life, the richness of species steadily increases. What is now emerging is a considerably more detailed picture of this developmental trajectory.

One key conclusion is that the intestinal microbiota forms an ecosystem that takes a long time to mature. Even at 5 years of age, the system is incomplete. The maturation process can look very different from one child to another, and take varying lengths of time.

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