Microbiota in preterm neonates
Objective: This study aimed to explore the distribution of intestinal and pharyngeal microbiota on the first day of life in preterm infants and compare the composition of microbiota in different modes of delivery.  Methods: This study included 44 late preterm infants with a gestational age of 34-36 weeks who were hospitalized in the Neonatal Intensive Care Unit (NICU) of Chengdu Fifth People's Hospital. Stool and throat swab samples were collected from the preterm infants on the first day of life and were divided into cesarean section and vaginal delivery groups based on the mode of delivery. Illumina NexSeq high-throughput sequencing technology was used to sequence the V3-V4 hypervariable region of the 16S rRNA gene of all bacteria in the samples, obtaining microbiota structure data. Based on the sequencing results, a Venn diagram was created to identify shared operational taxonomic units (OTUs) in the intestines and pharynges. Microbial analysis was conducted at the phylum and genus levels, and a and ß diversity comparisons were performed. Results: 1) Birth weight, gender, and mode of delivery did not significantly affect the microbial colonization of the intestines and pharynges of preterm infants on the first day after birth (p>0.05), while gestational age at birth may have significant influence (p=0.001). 2) More OTUs were detected in the pharynges than in the intestines, with a total of 819 shared OTUs between the two. Proteobacteria, Firmicutes, and Bacteroidota were the dominant phyla in both. There were no statistically significant differences in relative abundances, composition, and a and ß diversity (p>0.05) of microbiota between intestines and pharynges. At the genus level, Streptococcus had a lower relative abundance in stool samples (0.5%) compared to throat samples (0.5% vs. 22.2%, p=0.003). 3) When comparing cesarean section and vaginal delivery groups, the relative abundance of Streptococcus in pharyngeal samples was 26.2% in the cesarean section group much higher than the 3.8% in the vaginal delivery group (p=0.01). There were no statistically significant differences in the composition, relative abundance, or a and ß diversity of the dominant phyla in the pharyngeal microbiota between the two delivery modes (p>0.05). 4) There are differences in the composition and relative abundance of the dominant phyla and genera of the intestinal and pharyngeal microbiota on the first day of the same preterm infant, with specific microbiota. Conclusion: The early postnatal period is a critical time for the establishment of an infant's microbiota. Gestational age at birth may influence microbial colonization, while birth weight, gender, and mode of delivery do not significantly affect the microbial colonization of preterm infants on the first day after birth. Overall, there is a high similarity in the intestinal and pharyngeal microbiota of preterm infants on the first day after birth, but for individuals, there are differences in the intestinal and pharyngeal microbiota of preterm infants, further validation is required with a larger sample size.