Characterization of gut microbiota in preterm infants at discharge: a single-center observational study

Abstract

Background: The gut microbiota plays a crucial role in the health and development of preterm infants. Although previous studies have investigated the colonization and influencing factors of gut microbiota in this population, the specific characteristics at discharge and their associated factors remain poorly understood. This cross-sectional study aimed to characterize the gut microbiota composition of preterm infants at discharge across gestational age (GA) subgroups and identify the key associated clinical factors. Methods: This study enrolled 103 preterm infants (GA, 28–36+6 weeks) and 32 term infants admitted to the neonatal department of The Second Affiliated Hospital of Guangxi Medical University between December 2021 and December 2023. Preterm infants were stratified into three subgroups: very preterm (VP, 28– 31+6 weeks), moderately preterm (MP, 32–34+6 weeks), and late preterm (LP, 35–36+6 weeks) groups. Fecal samples collected 0–2 days before discharge were analyzed by 16S rRNA sequencing to determine microbial composition. Clinical correlations were assessed using Wilcoxon/Kruskal-Wallis tests, Principal Coordinate Analysis (PCoA), Mantel tests, and Spearman correlations, with subgroup analyses for antibiotic exposure and extrauterine growth restriction (EUGR). Results: At discharge, the gut microbiota of preterm infants was predominantly composed of Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes, with Firmicutes abundance showing significant intergroup variation (P=0.02). Genus-level analysis revealed significant differences in Enterococcus (P=0.03) and Clostridium (P=0.03) across GA subgroups. PCoA demonstrated distinct β-diversity among groups (P=0.005), which correlated negatively with postmenstrual age (PMA, R2=0.096, P<0.001) and positively with formula feeding (R2=0.137, P<0.001). Enterococcus negatively associated with GA, birth weight, PMA, and weight at discharge (all P<0.01), but positively with formula feeding (P<0.001). Subgroup analyses further revealed: (I) enrichment of Klebsiella and Streptococcus in VP infants compared to MP infants (PMA-matched), (II) reduced Bifidobacterium and Clostridium in late-preterm infants exposed to antibiotics, and (III) elevated Enterococcus and Staphylococcus in infants with EUGR, collectively linking microbiota composition to infant maturity, feeding practices, and growth outcomes. Conclusions: The development and evolution of the gut microbiota in preterm infants are jointly influenced by maturational and exogenous factors. While maturational processes primarily drive microbiota establishment in infants with lower GA, exogenous factors (e.g., feeding, antibiotics) exert stronger influence in those with higher GA. Notably, despite comparable PMA at discharge, VP infants exhibited reduced microbial diversity. Clinical interventions such as antibiotic administration significantly decreased Bifidobacterium abundance, whereas EUGR was associated with opportunistic genera (Enterococcus/Staphylococcus). These findings underscore the need for GA-stratified clinical strategies to promote healthy microbiota development and mitigate long-term health risks in preterm infants.