Bifidobacterium longum subspecies infantis: champion colonizer of the infant gut

Abstract

Oligosaccharides are abundant in human milk. Production of these highly diverse structures requires significant energy expenditure by the mother and yet these human milk oligosaccharides offer no direct nutritive value to her infant. A primary function of human milk oligosaccharides is to shape the infant's intestinal microbiota with life-long consequences. Bifidobacterium longum subspecies infantis (B. infantis) is unique among gut bacteria in its prodigious capacity to digest and consume any human milk oligosaccharide structure, the result of a large repertoire of bacterial genes encoding an array of glycosidases and oligosaccharide transporters not found in other bacterial species. In vitro, B. infantis grows better than other bacterial strains in the presence of human milk oligosaccharides, displays anti-inflammatory activity in premature intestinal cells, and decreases intestinal permeability. In premature infants, B. infantis given in combination with human milk increases B. infantis and decreases Enterobacteriaceae in the feces. Probiotics containing B. infantis decrease the risk of necrotizing enterocolitis in premature infants. Colonization with B. infantis is also associated with increased vaccine responses. Probiotic organisms have historically been selected based on ease of production and stability. The advantages of B. infantis, selected through coevolution with human milk glycans, present an opportunity for focused manipulation of the infant intestinal microbiota.

Figures

Figure 1

Systematic structural analysis of milk oligosaccharides from multiple mammalian species. Human milk (a) has a higher degree of oligosaccharide polymerization with about 70% fucosylated structures (upper structure) and less than 20% sialylated structures (lower structure, exclusively N-acetylneuraminic acid). Nonhuman primate milk (b) varies with species with 20–65% fucosylated structures (upper structure) and 10–45% sialylated structures (lower structure, both N-acetylneuraminic acid and N-glycolylneuraminic acid). Other mammals (c) show the least degree of polymerization, less than 5% fucosylated structures and up to 70% sialylated structures (lower structure, both N-acetylneuraminic acid and N-glycolylneuraminic acid) (,–83). Red triangle = fucose, yellow circle = galactose, blue square = N-acetylglucosamine, blue circle = glucose, purple diamond = N-acetylneuraminic acid, and light blue diamond = N-glycolylneuraminic acid.