*3.1.1 Safety*

*Prebiotics and Probiotics - Potential Benefits in Nutrition and Health*

Our body hosts a vast, diverse community of stable and varying microorganisms that are referred to as microbiota. The gut is the niche with the highest number and diversity of micro-organisms, containing over 1014 microbial cells, 10 times the amount of somatic and germinal cells in our body. The microbes that inhabit our

Gut microbiota is an open ecosystem that contains a broad diversity of metabolically active microbes that coexist in space and time and play a relevant role in the health of their host. The gut microbiota is considered a metabolic organ that is adaptable and rapidly renewable. There is a mutually beneficial interplay between

The relationship between the lymphatic system and gut microbiota in early stages of life is crucial to the appropriate development of interactions between mucosal cell communities and systemic immunomodulation [5]. Animals with a sterile gut have been proven to be highly vulnerable to infections, which demonstrate the important role that gut microbiota plays in the immune system [4].

Bacterial colonization of the newborn's gut is influenced by a variety of factors such as gestation and delivery and breast-feeding mode [6]. HBM is an excellent continuous source of commensal bacteria for the infant gut. Evidence has been provided of a vertical transfer of bacteria from mother to child via breast milk [7, 8]. The fact that facultative anaerobic bacteria in newborn's gut are the predominant bacterial community in HBM microbiota is not a chance. These bacteria play a key role in the prevention of infections in the newborn [9]. Gut microbiota disorders (dysbiosis) in

During the first week of life, the total bacterial count and, more specifically, anaerobic bacteria count progressively increase. The feeding mode of the newborn has a decisive impact on bacterial gut colonization. Bifidobacteria, lactobacilli, and Gram-positive cocci predominate in the feces of breastfed infants, whereas the bifidobacteria count is lower in the feces of formula-fed infants, with the predominance of bacteroides, clostridia, and coliforms [11–13]. Differences in the composition of newborn's gut microbiota based on the type of feeding could be the clue to identifying the bacteria that exert protective effects to breastfed infants [4].

and 104

ufc/mL. This means

ufc [14].

to 107

the first stages of life reportedly precede the development of atopy [10].

Bacterial concentrations in HBM range between 102

that an infant ingesting over 800 ml of milk a day would receive 105

Therefore, HBM is a primary source of commensal and probiotic bacteria to the infant and plays a key role in the initial colonization of the gut. Some bacteria isolated from HBM have proven to have immunomodulatory and anti-infective effects. Therefore, the protective effects of HBM may be conferred by these bacteria. Supplementation of infant formulae with probiotic bacteria isolated from HBM could help improve gut microbial balance in formula-fed infants, thereby mimick-

Evidence has been published that probiotics modulate mucosal and systemic immune function, improve intestinal barrier function, and exert metabolic effects on the host [4]. Some of the lactobacillus strains isolated from HBM [15] have been reported to compete with enteropathogenic bacteria for nutrients and epithelium

**2. Gut microbiota**

gut are known as gut microbiota [4].

the host and gut microbiota [4, 5].

**2.1 Gut microbiota and immunity**

**4**

**3. Probiotics**

ing the beneficial effects of HBM.

Formulae supplemented with probiotics do not raise safety concerns with regard to growth and adverse effects [19]. There are sufficient data supporting the safety of probiotics for infants older than 6 months. However, data on the use of probiotic supplementation in infants younger than 4 months are more limited. Studies in breastfed infants younger than 6 months who received a formula supplemented with either *Lactobacillus fermentum* CECT5716 or *Lactobacillus rhamnosus* GG revealed that formulae were well tolerated and had no adverse effects on growth either during the study period or at 3–5 years of age [20–23]. A recent study revealed that growth and food tolerance improved in premature infants >30 weeks of gestational age fed with a formula supplemented with *Saccharomyces boulardii,* and no adverse effects were detected [24].
