316 - Comparative assessment of very low birthweight preterm infant oral and gastric microbiomes and bacterial load

Publication Number: 3305.316

Thao Ho, University of South Florida, Tampa, FL, United States; Melissa Olsen, University of South Florida, Tampa, FL, United States; Ryan Pace, University of South Florida, Tampa, FL, United States

Background: The oral and gastric microbiomes of very low birthweight (VLBW, < 1500 g) preterm infants represent critical yet underexplored ecosystems that may shape early immune, metabolic, and gastrointestinal development. Prolonged hospitalization, parenteral nutrition, antibiotics, and delayed enteral feeding can disrupt normal microbial colonization. Shifts in these early microbial communities may influence susceptibility to necrotizing enterocolitis, feeding intolerance, and long-term health outcomes. However, key gaps remain in understanding how oral and gastric tract microbial succession occurs in preterm infants, how these sites interact with maternal and environmental sources, and how early interventions might promote beneficial colonization trajectories and health outcomes in this high-risk population.

Objective: To characterize and compare the oral and gastric microbiomes and bacterial load of VLBW preterm infants.

Design/Methods: In this pilot study, oral swabs (n=43) and/or gastric aspirate (n=26) samples were aseptically collected from VLBW infants (n=21). Gastric aspirate samples were collected prior to feedings and oral swabs following feedings. DNA was extracted and the bacterial 16S rRNA gene (V4 region) was sequenced. Bacterial load was quantified using a TaqMan assay. Microbial beta diversity was assessed by Bray-Curtis dissimilarity and alpha diversity by observed genera, Shannon, and Simpson indices. Statistical significance was declared at p< 0.05 or FDR p< 0.1 after correction for multiple comparisons.

Results: Median (IQR) bacterial loads (16S rRNA gene copies/uL, log10) from oral swabs (7.07 [6.44-7.27]) and gastric samples (6.80 [6.44-6.96]) did not differ (p=.012). Numerous genera were identified as differentially abundant: including higher relative abundance of Klebsiella, Enterobacter, Acinetobacter, Ureaplasma, and Staphylococcus in gastric aspirate samples, and higher relative abundance of Streptococcus in oral samples. Beta diversity, but not alpha diversity, significantly differed by sample type (p=0.001, r2=0.113). Within sample type, oral bacterial load, but not gastric, was positively associated with all alpha diversity metrics (p < 0.001) and with beta diversity (p=0.03, r2=0.052).

Conclusion(s): These findings highlight distinct microbial community structures between the oral and gastric sites of VLBW preterm infants, suggesting differential colonization dynamics despite comparable bacterial loads. Understanding these early microbial patterns may inform strategies to support beneficial colonization and reduce infection-related morbidities in this vulnerable population.