The gut microbiota plays an important role in various aspects of human health and metabolism. The composition of the intestinal microbiota undergoes major changes in the first 2-3 years of life and in old age. The initial contact of newborn babies with microbes is crucial in determining the type of infant gut microbiota. This is an important determinant of general health status and immunity in later life. For a long time, it was believed that the first contact with bacteria occurred during childbirth, in contrast to children born by cesarean section, the intestinal microbiota of children born vaginally was more abundant and diverse. Some recent studies have shown the presence of bacterial or bacterial nucleic acids in umbilical cord blood, amniotic fluid, and placenta [1]. Among the contributors to the formation of the gut microbiota, early feeding and type of feeding is an important factor in the composition and function of the gut microbiota. Breast milk contains more than 200 oligosaccharides that ferment in the colon and stimulate the growth of certain bacteria. In addition to this “prebiotic effect”, breast milk is a source of live bacteria, including staphylococci, streptococci, bifidobacteria, lactic acid bacteria, beneficial viruses, and even fungi (human milk mycobiome) [2]–[4]. Probiotics, defined as live microbial preparations that have a positive effect on the health of the host, represent a rapidly expanding field. The demand for probiotics in clinical applications and as functional foods is increasing dramatically despite limited understanding of their mechanisms. Numerous randomized controlled trials using probiotics in infants; It has shown promising results in the prevention and treatment of common diseases such as diarrhea and allergies [5] –[7]. Possible mechanisms of probiotic intervention include the promotion of a non-immunological intestinal defense barrier, which includes the normalization of increased intestinal permeability and altered gut microecology. Another possible mechanism of probiotic intervention is the improvement of the immunological barrier of the gut, which produces an intestinal stabilizing effect, particularly through local immune globulin A (IgA) responses and mitigation of intestinal inflammatory responses [8]. However, little is known about whether probiotics can benefit healthy babies.

Among a number of bacterial species found in the GI tract, Bifidobacterium and Lactobacillus species have been extensively investigated in human and animal studies. The 2 species are recognized to have health-promoting properties and are added to commercial foods such as infant formula and used in pharmaceutical probiotics to strengthen the protective gut microbiota, thereby improving the gut microbial balance. Bifidobacterium infantis releases bioactive factors and prevents transepithelial resistance declines caused by TNF-a and IFN-g to maintain intestinal epithelial cell barrier function [9]- [10]. Bifidobacterium bifidum increases local IgA levels in the gut and prevents diarrhea and scattering of rotavirus [11]-[12]. Lactobacillus helveticus inhibits the invasion of intestinal epithelial cells Campylobacter jejuni [13]. The surface layer protein may exhibit anti-inflammatory effects by reducing the activation of NF-kB on intestinal epithelial cells [14]-[15].