A new group of beneficial bacteria discovered in the gut of children during weaning

An international research team has discovered the existence of a new group of beneficial bacteria that becomes prevalent in the intestines of children during weaning. The study was published in the journal Cell and could contribute to the development of targeted probiotics to support children's growth and development.

"Weaning is an important but also delicate period in the life of an infant, because the immune defences offered by the mother's milk are gradually replaced by the development of an individual 'active' immunity, for which the gut microbiome plays a relevant role", explains Paola Mattarelli, professor at the Department of Agricultural and Food Sciences of the University of Bologna, among the authors of the study. "The great geographical variability of the diets offered to children during weaning, however, makes it difficult to reconstruct the development process of the microbiome and the action of the different bacteria that make it up."

Breast milk plays a key role in shaping the microbiome of newborns. In particular, the oligosaccharide component modulates the gut microbiome and its co-evolution with the child's organism: in fact, oligosaccharides are not digested by the host but are selectively fermented by the beneficial gut bacteria. The weaning phase, with the introduction of solid foods associated with breast milk, enriches this process and may prove decisive in defining the structure and functions of the microbiome.

To understand how weaning contributes to shaping the microbiome - also in relation to differences in the diets of children in different parts of the world - the researchers followed the development of 267 children in Dhaka, Bangladesh, from birth to two years of age. Most infants were exclusively breastfed for the first six months, and even later, during weaning, the introduction of solid food was always associated with breast milk.

Precisely during this “mixed” weaning period, the researchers identified the presence of a new bacterial group belonging to the species Bifidobacterium longum, a bifidobacteria species typical of the healthy gut microbiota, in the children's microbiome.

"This new group shows the unique ability to ferment both oligosaccharides from breast milk and fibres from solid foods, and its abundance in the gut increases when children's diets are diversified", says Professor Mattarelli. "In addition, it was possible to confirm that this new bacterial group interacts with many other microbial species: it therefore also plays an important role in general gut ecology and metabolism."

The new bacterial group identified is different from the Bifidobacterium longum species already known, such as Bifidobacterium subsp. infantis, the most abundant species in exclusively breastfed infants during the first months after birth. The results suggest that this new group may belong to a new subspecies: further research is currently underway to ascertain this.

The scholars also point out that the prevalence of these bacteria in the Bangladeshi context is not found in the same way in Western countries. This suggests that 'mixed' weaning up to two years of age may have positive effects on the development of the microbiota. All results that could lead to the development of targeted diets and foods to promote healthy growth in children.

The study was published in the journal Cell under the title "A distinct clade of Bifidobacterium longum in the gut of Bangladeshi children thrives during weaning". The research was carried out by researchers from Nestlé Research (Switzerland), in collaboration with the Broad Institute of MIT and of Harvard (Cambridge, MA, USA), the University of Bologna (Dr Monica Modesto and Prof Paola Mattarelli, Department of Agricultural and Food Sciences), and the International Center for Diarrheal Disease Research in Dhaka, Bangladesh.