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Bacteria in digestive tract may help infants digest milk more effectively than adults

LoCascio RG. Appl Environ Microbiol. 2010;76:7373-7381.

Strains of bacteria that dominate infants’ digestive tracts enable them to digest and utilize nutritional components of milk more efficiently than adults.

“Human milk oligosaccharides are the third-largest solid component of milk. Their structural complexity renders them non-digestible to the host,” researchers from the University of California, Davis, and Utah State University said in a press release.

“Bifidobacterium longum strains often predominate the colonic microbiota of exclusively breast-fed infants. Among the three recognized subspecies, B. longum subsp. infantis achieves high levels of cell growth on human milk oligosaccharides and is associated with early colonization of the infant gut,” they said.

The researchers used whole-genome microarray comparisons to associate genotypic biomarkers among 15 B. longum strains exhibiting various human milk oligosaccharides utilization patterns. They identified five distinct gene clusters on B. longum that were conserved, showing little or no variation, across all strains capable of growth on human milk oligosaccharides and diverged in strains incapable of growing on human milk oligosaccharides.

The findings suggest that B. longum has at least two distinct subspecies: B. longum subsp. infantis, which is adapted to utilize milk carbon and is found predominantly in children’s digestive tracts, and B. longum subsp. longum, which is specialized for plant-derived carbon metabolism and is associated with the digestive tracts of adults.

“Although early gut colonization is likely dependent on a multitude of dietary and nondietary factors, the delivery of complex oligosaccharides through milk creates an ideal and unique nutrient niche for the establishment of, and colonization by, B. longum subsp. infantis strains,” the researchers said. “During weaning, a gradual transitioning from milk-based to plant-based diets generates a shift in carbon availability in the gastrointestinal tract favorable for the expansion and formation of an adult-like gastrointestinal tract microbiota.”

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