**1. Introduction**

Human breast milk (HBM) is a complex physiological fluid uniquely suited to nourish infants. Its composition is specifically adapted to the digestive system and nutritional and growth needs of infants. HBM does not only contain essential nutrients, but also a vast array of non-nutritional bioactive components and microbes (microbiota) that confer benefits to the health of infants in the short and long terms. The microbiota mediates bacterial colonization of the newborn gut and supports immune system maturation and metabolic and cognitive development. Protective constituents such as cytokines, oligosaccharides, and bacteria facilitate newborn's adaptation to the extrauterine environment [1, 2]. HBM has been long known to protect neonates and infants from infections. It has been suggested that this protective role could be regulated by the action of a group of components that might inactivate bacteria and viruses individually, additively, and synergistically [3].

Gut microbiota has effects on health, and HBM contributes decisively to its composition via its bacteria and oligosaccharides supply. In order to achieve the same health effects, infant formulae are supplemented with live bacteria (probiotics), which favor bifidobacteria and lactobacilli growth (prebiotics) or a combination of these components (symbiotics).
