LAUSR

To compare the gut microbiota of healthy infants based on specific interactions of delivery modes and feeding types, we recruited 62 healthy babies who were followed up for 2 years from our previous cohort study of 91 infants (the rest were lost to follow-up). They were exclusively fed breast milk or specific formulas for more than 4 months after birth. The fecal bacterial composition was tested at 40 days, 3 months, and 6 months of age. Solid foods were introduced from 4 to 6 months of age and thus did not affect the microbiota before 4 months of age. According to the different delivery modes (i.e., vaginal delivery, VD, or cesarean section delivery, CS) and feeding types (i.e., breast-fed, br, or formula-fed, fo), the infants were assigned to four different groups, namely, the VD-br, VD-fo, CS-br, and CS-fo groups. We found that at 40 days of age, the α diversity (reported as the Shannon index) was lower in the br infants than in the fo infants. At 3 months of age, the α diversity was significantly lower in the CS-br group, although significant differences were not observed after solid food introduction. Bifidobacterium represented the most predominant genus in all groups at all time points, followed by Enterobacteriaceae. At 40 days of age, the abundance of Bifidobacterium was much higher in the CS-br group than in the CS-fo group but did not differ between the VD-br and VD-fo groups. The differences in Bifidobacterium disappeared at 3 and 6 months of age among the different groups. At 40 days of age, the abundance of Streptococcus and Enterococcus was much lower in the br infants than in the CS-fo group. At 3 months of age, Enterococcus was significantly lower in the CS-br group than in the fo infants, although for infants delivered by VD, the difference between feeding types was not significant. The specific interaction of delivery modes and feeding types has a large impact on the infants' gut microbiota. Breastfeeding and VD may decrease the potential adverse effects of formula feeding or CS delivery on gut microbiota, thus leading to a more stable and beneficial gut environment for infants.