Establishment of gut microbiota in term and preterm infants: evaluation by culture-independent methods

Background The establishment of a healthy gut microbiota (GM) in term and preterm infants can influence several clinical outcomes. The mechanisms driving GM establishment have been described partially, and the relationship between GM and microbiota from human milk (HM) and saliva is still a matter of debate. Little is known about GM in moderately preterm infants (MPIs). Aim of the study To characterize the establishment of GM, in relation to saliva and HM microbiota, in term and preterm infants, with a focus on MPIs. Methods Newborns were recruited at the Neonatal Unit of Sant’Orsola-Malpighi Hospital: • Group A: term infants, born to vaginal delivery, exclusively breastfed, not exposed to antibiotic/probiotic. • Group B: MPIs. • Group C: very preterm infants (ongoing sample collection). For each group, stools, HM and saliva were collected at different time points. Results Group A GM was dominated by Bifidobacteriaceae, followed by Enterobacteriaceae and Streptococcaceae. Streptococcaceae were the most represented family in HM, followed by Bifidobacteriaceae and Staphylococcaceae. Oral microbiota was largely dominated by Streptococcaceae. Microbiota from infant’s saliva, infant’s stools and HM clustered separately. Several OTUs were shared between at least two body sites. Group B GM of MPIs was dominated by Enterobacteriaceae, followed by Bifidobacteriaceae. Staphylococcaceae and Streptococcaceae were the most abundant families in HM, while Bifidobacteriaceae were low. Streptococcaceae dominated saliva microbiota. Longitudinal analysis of HM, stools and saliva microbiota showed some remarkable differences among infants, and even between twins, which could not be attributed to any clinical or environmental confounder. Conclusions Data from MPIs show that the characteristics of the establishment of GM in these infants are peculiar and more similar to very preterm than to term infants. The establishment of GM in MPIs is thus worth to be further explored, given the specific short- and long-term clinical risks of these infants.