Breastfeeding provides the ideal nutrition for infants. Human milk contains a plethora of functional ingredients which foster the development of the immune system. The human milk microbiota predominantly contributes to this protective effect. This is mediated by various mechanisms, such as an antimicrobial effect, pathogen exclusion and barrier integrity, beneficial effects on the gastrointestinal microbiota, vitamin synthesis, immunity enhancement, secreted probiotic factors, and postbiotic mechanisms. Therefore, human milk is a good source for isolating probiotics for infants who cannot be exclusively breastfed. One such probiotic which was isolated from human milk is Limosilactobacillus fermentum CECT5716. In this review, we give an overview of available interventional studies using Limosilactobacillus fermentum CECT5716 and summarise preclinical trials in several animal models of different pathologies, which have given first insights into its mechanisms of action. We present several randomised clinical studies, which have been conducted to investigate the clinical efficacy of the Limosilactobacillus fermentum CECT5716 strain in supporting the host’s health.

Background: Early life nutrition is crucial for the development of the gut microbiota that, in turn, plays an essential role in the maturation of the immune system and the prevention of infections. Objectives: The aim of this study was to investigate whether feeding synbiotic infants and follow-on formulas during the fi rst year of life reduces the incidence rate (IR) of infectious diarrhea compared with standard formulas. Secondary endpoints included the IR of other infectious diseases as well as fecal milieu parameters. Methods: In this double-blind, controlled trial, 460 healthy, 1-mo-old infants were randomly assigned to receive a synbiotic [galacto-oligosaccharides (GOS)/ Limosilactobacillus fermentum CECT 5716] (IF, n = 230) or a control formula (CF, n = 230) until 12 mo of age. A reference group of breastfed infants (HM, n = 80) was included. Data on infections were recorded throughout the study period and stool samples were collected at 4 and 12 mo of age. Results: IR of infectious diarrhea during the fi rst year of life was 0.60 (CF), 0.56 (IF), and 0.29 (HM), with no statistically signi fi cant difference between groups. The IR of lower respiratory tract infections, 1 of the secondary endpoints, however, was lower in IF than in CF [0.79 compared with 1.01, IR ratio = 0.77 (0.60 - 1.00)]. Additionally, fecal pH was signi fi cantly lower at 4 mo ( P < 0.0001), whereas secretory IgA was signi fi cantly higher at 12 mo of age ( P = 0.015) in IF compared with CF. Conclusions: Although no difference is observed in the incidence of diarrhea, consumption of a synbiotic formula containing L. fermentum CECT5716 and GOS in infancy may reduce the incidence of lower respiratory tract infections and affect the immune system and fecal milieu. Additional research is warranted to further investigate the potential interaction of the gut - lung axis.