Fig. 3

Venn diagram of bacterial genera hypothesized to contribute to the infant gut microbiome. Aagaard and colleagues [9] hypothesized that bacteria translocate from the mother’s oral cavity into the placenta, contributing to in utero colonization of the fetal gut. They further suggest that placentas contain low abundance communities of commensal bacteria. However, 36% of the bacterial genera found by Aagaard and colleagues [9] also appear on the list of contaminants found in reagents by several independent research groups as reported by Salter and colleagues [90]. Not all genera were included for each individual microbiome due to space constraints. Genera found in the infant gut [2, 101, 102, 105, 148] include taxa described in both vaginally and cesarean section-delivered babies [101, 105] and show a substantial overlap with genera found in the adult gut microbiome [145,146,147], but little overlap with taxa found in the placenta [9, 91] or as contaminants [85,86,87,88,89,90,91]