The preterm human milk microbiota fluctuates by postpartum week and is characterized by gestational age and maternal BMI

Evidence suggests that the type of nutrition fed to preterm infants influences their intestinal microbiome and immunity. However, few studies have conducted a longitudinal analysis of the microbiota of mothers own milk and the factors shaping its composition. Furthermore, the microbiota of pasteurized donor human milk and infant formula have not been extensively investigated. Here, we examine the microbiota of 238 MOM, 30 PDHM, and 73 formula samples from a cohort of 72 preterm infants using 16S rRNA sequencing. We find differences in the microbial diversity and composition between nutrition types. Additionally, we demonstrate that the microbiota of MOM exhibits temporal fluctuations and has associations with several maternal factors. Lastly, we identify three microbiota community clusters within MOM, termed lactotypes, that have distinct taxonomic compositions and maternal factors. Collectively, our findings lay the foundation for exploring the relationship between the microbiota of nutrition and preterm infant health outcomes.