Advances in lactation: exploring the role of human breast milk microbiota in neonatal gut maturation

The neonatal microbiota plays a central role in shaping gastrointestinal and immune system maturation, laying the foundation for lifelong health. Prenatally, bacteria in the amniotic fluid and meconium, likely derived from the maternal microbiota, prime the fetal immune system to tolerate beneficial microbes postnatally. At birth, the neonate acquires its initial microbiota through the birth canal or environmental exposure, with breast milk delivering human milk oligosaccharides that selectively nourish beneficial bacteria, such as Lactobacillus and Bifidobacterium, fostering a protective gut microbiota. Meconium in the colon further supports this process by acting as a barrier against pathogens while promoting colonization by commensal microbes. These early microbial communities enhance intestinal barrier function through tight junction maturation, reduce permeability, and bolster immune defenses, mitigating infection risks. As infants transition to solid foods, microbial diversity increases, supporting intestinal villi development, nutrient absorption, and dietary adaptability. By approximately 3 years of age, the gut microbiota stabilizes, driving critical roles in digestion, vitamin synthesis, and inflammation regulation. This review synthesizes current evidence on the dynamic interaction and influence of maternal factors and breast milk composition on neonatal microbiota development, highlighting current insights into their implications for the infant's immune system and gastrointestinal development.