Factors influencing the intestinal microbiota composition in early infancy were examined in a study of 1032 infants. The study found that mode of delivery, type of feeding, gestational age, hospitalization, and antibiotic use were the most important determinants of the gut microbiota. Infants born via cesarean section had lower levels of bifidobacteria and Bacteroides, and higher levels of C. difficile compared to those born vaginally. Exclusively formula-fed infants had higher levels of E. coli, C. difficile, Bacteroides, and lactobacilli compared to breastfed infants. Hospitalization and prematurity were associated with higher prevalence and counts of C. difficile. Antibiotic use by the infant was associated with lower levels of bifidobacteria and Bacteroides. Infants with older siblings had slightly higher levels of bifidobacteria. The study concluded that term infants born vaginally and breastfed exclusively had the most beneficial gut microbiota, with higher levels of bifidobacteria and lower levels of C. difficile and E. coli. The study used real-time PCR to quantify bacterial groups and species in fecal samples. The findings highlight the importance of factors such as mode of delivery, feeding type, and antibiotic use in shaping the gut microbiota in early infancy.Factors influencing the intestinal microbiota composition in early infancy were examined in a study of 1032 infants. The study found that mode of delivery, type of feeding, gestational age, hospitalization, and antibiotic use were the most important determinants of the gut microbiota. Infants born via cesarean section had lower levels of bifidobacteria and Bacteroides, and higher levels of C. difficile compared to those born vaginally. Exclusively formula-fed infants had higher levels of E. coli, C. difficile, Bacteroides, and lactobacilli compared to breastfed infants. Hospitalization and prematurity were associated with higher prevalence and counts of C. difficile. Antibiotic use by the infant was associated with lower levels of bifidobacteria and Bacteroides. Infants with older siblings had slightly higher levels of bifidobacteria. The study concluded that term infants born vaginally and breastfed exclusively had the most beneficial gut microbiota, with higher levels of bifidobacteria and lower levels of C. difficile and E. coli. The study used real-time PCR to quantify bacterial groups and species in fecal samples. The findings highlight the importance of factors such as mode of delivery, feeding type, and antibiotic use in shaping the gut microbiota in early infancy.