Links Between Gut Microbiota of Uruguayan Infants, Breast Milk Composition, and Maternal Factors During Exclusive Breastfeeding

BackgroundGiven the links between early gut microbiota, breastfeeding, and maternal physiology, we characterized the intestinal microbiota of infants during exclusive breastfeeding (mean=5.4 months), examining its associations with breastmilk composition, fecal IgA, and maternal factors in Uruguayan primiparous mothers, with vaginal (V, n=20) or cesarean-section delivery (CS, n=14). MethodsWe analyzed fecal microbiota via 16S rRNA V4 sequencing and quantified stool IgA, breastmilk components (antibodies, hormones, macronutrients) using ELISA and standard biochemical methods. ResultsPrincipal Coordinates Analysis showed separation by delivery mode (PCo1:44.6%, PCo2:14.2%). Samples of CS-group displayed lower relative abundance (RA %) of Bacteroidetes/Firmicutes ratio, higher RA of Proteobacteria (50.7%vs35.5%), and decreased Bacteroides (2.5%vs31.8%) than V-group. Biochemical parameters didnt differ between groups. In the V-group, milk and fecal IgA correlated (r=+0.47), as did Bifidobacterium RA with milk IgA (r=+0.47). Fat content was associated with different microbial taxa in both groups. Only in CS-group milk carbohydrates correlated with Bifidobacterium (r=-0.679) and maternal stress with Flavonifractor in CS-group (r=+0.461). ConclusionResults indicate delivery mode can exert persistent impact on infant gut microbiota until the introduction of complementary feeding. Differences in correlation patterns between groups suggest distinct regulatory mechanisms of microbiota, possibly linked to physiological processes that differ according to delivery mode. ImpactO_LIThis is the first study to assess the gut microbiota composition of exclusively breastfed infants born to Uruguayan mothers, in parallel with analyses of breast milk composition and maternal perceived stress C_LIO_LIThe mode of delivery was associated with differences in gut microbiota composition at a mean age of 5.4 months. C_LIO_LIDifferent associations between milk composition and maternal perceived stress with predominant microbial taxa were found according to the type of delivery. C_LIO_LIThese findings provide a basis for studies on microbiota regulatory mechanisms influenced by maternal physiology according to delivery mode C_LI