Early-Life Development of the Intestinal Microbiome in Preterm and Term Infants Hospitalized in the Neonatal Intensive Care Unit

This prospective cohort study investigated the longitudinal compositional changes of the gut microbiome across different gestational age groups, from birth to six months' corrected age for prematurity. Fecal samples (n = 709) from 349 neonates [51 very preterm, 195 moderate-to-late preterm, and 93 full-term infants] were analyzed. Proteobacteria, Firmicutes, and Bacteroidetes constituted the core microbiome of the meconium. Proteobacteria and Firmicutes were the dominant phyla before discharge, whereas Firmicutes was the most dominant phylum in all groups after discharge. <i>Ralstonia</i> was the most prevalent genus in the meconium of preterm infants. After discharge, the relative abundance of <i>Veillonella</i> continued to increase in all gestational groups (<i>p</i> = 0.011 for very preterm, <i>p</i> < 0.001 for moderate-to-late preterm and full-term). By six months corrected age, differences in the gut microbiota composition became less pronounced between the groups. The α-diversity of meconium was highest across all groups, and this significantly decreased during the neonatal intensive care unit stay and increased thereafter. The β-diversity was significantly different (<i>p</i> < 0.05) but of limited practical significance (<i>R</i>² < 0.1). The differences between groups diminished as infants grew older, indicating that preterm infants were able to achieve a balanced gut microbiota and overcome dysbiosis.