Abstract Background The respiratory microbiota influences infant immune system maturation. Little is known about how perinatal, physiological, and environmental exposures impact the nasal microbiota in preterm infants after discharge, or nasal microbiota differences between preterm and healthy full-term infants. Methods Nasal swabs (from 136 preterm and 299 full-term infants at mean postmenstrual age of 45 weeks from the prospective Basel-Bern Infant Lung Development cohort) were analyzed by 16S-rRNA gene amplification and sequencing (Illumina MiSeq). Associations were tested with multivariable linear regression and principal coordinate analysis. Results Presence of older siblings in preterm infants was associated with β-diversity (PERMANOVA p = 0.001) and an increased abundance of Moraxella and Haemophilus . The nasal microbiota of preterm infants exhibited a distinct composition compared to that of full-term infants (PERMANOVA, R 2 = 0.014, p = 0.001), characterized by a reduced abundance of the Moraxella and Dolosigranulum genera (ANCOM-BC, p < 0.05). Conclusion Our results indicate that, despite both infant groups having similar nasal microbiota patterns, there are some disparities which suggest that prematurity influences the initial microbiota colonization. In preterm infants the presence of older siblings had an effect on the nasal microbiota, whereas perinatal and early postnatal factors did not show significant effects. Impact Presence of older siblings affected the nasal microbiota of preterm infants. This study demonstrated that microbiota composition differs between full-term and preterm infants, with a lower abundance of Moraxella and Dolosigranulum in preterm infants. Examining the differences in nasal microbiota between preterm and full-term infants may contribute to understanding the trajectory of the bacterial component of the nasal microbiota of preterm infants.
