The infant gut microbiota: a narrative review about development and external determinants.

This narrative review examines the development of the infant gut microbiota during the early months of life, highlighting the impact of delivery mode and feeding practices on microbial colonization and overall infant health. The search was conducted using the Virtual Health Library and PubMed databases, with the descriptors "gut microbiota" combined with "breastfeeding" (BF) and "infant formula." After screening, 18 articles were selected for final analysis. Findings indicate that cesarean section reduces initial gut microbial diversity by 30%-50% and decreases Bifidobacterium colonization, while increasing the abundance of Enterobacteriaceae and Clostridium. In contrast, exclusive BF supports a more favorable microbial profile, enriched in bifidobacteria, and contributes to immune system maturation. The literature also highlights the importance of other genera, including Lactobacillus, Veillonella, and Firmicutes, in regulating inflammation, producing short-chain fatty acids, and protecting against pathogens. Supporting vaginal birth and exclusive BF emerges as a key strategy to promote a more resilient and health-promoting gut microbiota during infancy.