Alterations in the gut microbiome during the first two months of life in preterm, low-birth-weight infants

Introduction: Over recent decades, the study of the bacterial microbiome has gained increasing attention due to its vital role in human health. The development of the gut microbiome is especially critical during infancy, as it supports nutrient absorption, metabolic regulation, and immune system maturation. Several perinatal factors, including delivery mode, gestational age, and health status, have been shown to influence micro -biome establishment. Preterm and low-birth-weight infants, in particular, face heightened vulnerability to disruptions in microbiome development, which may contribute to adverse health outcomes. Aims & Methods: This study aimed to analyze the longitudinal development of the gut microbiome in preterm, low-birth-weight neonates over the first two months of life and to identify microbial patterns and alterations associated with delivery mode, gestational age, and clinical conditions. The study cohort included 115 low-birth-weight preterm infants and 99full-term, normal-weight controls. Stool samples from preterm infants were collected at multiple time points between day 1 and day 61 of life and grouped into six age categories for analysis. In total, 819 stool samples were examined. DNA was extracted and amplified targeting the V3–V4 region of the 16S rRNA gene, followed by sequencing on the Illumina MiSeq platform. Microbiome data were analyzed using bioinformatic and statistical tools to assess taxonomic composition, alpha diversity, and beta diversity. Results: Significant differences in microbiome profiles were associated with gestational age, mode of delivery, postnatal age, maternal medication, and the presence of necrotizing enterocolitis (NEC). Bacterial com-munities began to stabilize between days 26 and 35. A total of 56 bacterial genera — including Bifidobacterium, Clostridium, Escherichia-Shigella, Gemella, Klebsiella, Lactobacillus, and Streptococcus — showed a positive correlation with infants’ age in days, while 31 genera — including Bacillus, Cutibacterium, Flavobacterium, Macrococcus, Pseudomonas, and Staphylococcus — were negatively correlated. Eighteen bacterial genera were associated with the mode of delivery at various time points. Genera such as Fusobacterium, Bacteroides, Entero-coccus, Streptococcus, Gemella, and Corynebacterium were more commonly associated with vaginal birth, while Staphylococcus, Rahnella, Yokenella, Millisia, Negativicoccus, Finegoldia, Haemophilus, Acinetobacter, Conservatibacter, Serratia, Stenotrophomonas, and Peptoniphilus were associated with Caesarean section delivery. Moderate differences in early-life microbiome composition were also ob -served between low-birth-weight preterm and full-term infants. Conclusion: Gut microbiome development in preterm, low-birth-weight newborns is strongly influenced by clinical and perinatal factors, particularly during the first month of life. Mode of delivery, gestational maturity, and disease presence such as NEC contribute to microbial variability and delayed community stabilization. These findings highlight the importance of early-life monitoring and tailored interventions to support healthy microbiome development in vulnerable neonates.