Human milk oligosaccharides and selfish (or not selfish) Bifidobacterium strains

Human milk is a rich source of components that contribute to shaping the infant gut microbiota through a variety of mechanisms. After lactose and lipids, human milk oligosaccharides (HMOs; Fig. 1) are the third most abundant components of human milk. One litre of mature human milk contains 5–20 g of these complex sugars, which often exceeds the amount of all human milk proteins combined. Oligosaccharide concentrations in colostrum are even higher [1]. To date, the molecular structures of more than 100 different HMOs have been characterized, but it is important to note that total amount and composition are highly variable between different women.