Spatiotemporal development of late and moderate preterm infant gut and oral microbiomes and impact of gestational age on early colonisatio

Microbiome research focusing on late and moderate preterm infants (LMPT 32 to 37 weeks gestation) is scarce, despite rising numbers of LMPT births, large burdens on healthcare systems, and increased risks of multiple morbidities that may be microbially related. In this longitudinal observational cohort study, 16S rRNA gene sequencing of 371 stool and 402 saliva samples collected at five time points between birth and 12 months corrected age (CA) was employed to describe spatial and temporal variability in the gut and oral microbiomes of 160 LMPT infants. Using available paired samples (n=337), potential relationships between stool and saliva microbes were interrogated. Additionally, the earliest LMPT samples (up to 60 days of life DOL) were compared with those from an existing dataset of extremely preterm infants (EP 26 weeks gestation) housed in intensive care. LMPT stool and saliva showed increasing alpha diversity with age and varied in microbial composition over time. Stool and saliva samples were taxonomically distinct at all time points; stool samples were initially dominated by Escherichia/Shigella, Klebsiella, and Streptococcus, with Bifidobacterium becoming the dominant genus from term equivalent age (TEA) and additional later contributions from Veillonella, Blautia, Prevotella, Faecalibacterium and genera from family Lachnospiraceae, whilst saliva samples remained largely dominated by Streptococcus throughout the first year, showing contributions from Staphylococcus earlier and Veillonella later. In contrast to LMPT infants, early shifts in alpha diversity or taxonomic composition were absent in EP infants. EP infants had lower stool and higher saliva alpha diversity than LMPT infants, and both sample types were taxonomically distinct from older groups, as both stool and saliva from EP infants remained dominated by Escherichia/Shigella over the first 60 DOL. The results highlight the unique trajectories of LMPT gut and oral microbiomes and further underscore the importance of gestational maturity in shaping microbial communities