Metataxonomic and bacterial culture studies of breast milk microbiota in premature infants: factors influencing its bacterial composition and diversity
Background: Breast milk represents the optimal feeding strategy for newborns, supporting not only nutrition but also the establishment of a unique microbiota. The bacterial composition and diversity of this microbiota are shaped by various maternal and infant-related factors.  Objectives: This single-center prospective study aimed to examine the breast milk microbiota and determine the maternal and infant-related factors influencing its composition and diversity over the time. Methods: We analysed 137 breast milk samples using bacterial culture and 16S rRNA gene sequencing, collected from 40 healthy mothers who delivered preterm infants via vaginal or cesarean section. All milk samples were collected exclusively using a breast pump. Results: Our results revealed a diverse bacterial community, with the dominant phyla being Bacillota, Pseudomonadota, Actinomycetota, and Bacteroidota. At the genus level, Staphylococcus, Acinetobacter, and Corynebacterium were the most prevalent. We defined a core breast milk microbiota comprising seven bacterial genera: Staphylococcus, Acinetobacter, Corynebacterium, Pseudomonas, Cutibacterium, Enterococcus, and Streptococcus. Notably, mothers with a postpartum body mass index (BMI) = 25 exhibited a significant decrease in the bacterial diversity of their breast milk microbiota. Longitudinal analysis findings suggested an increase in bacterial diversity over time, while the aerobic bacterial flora seemed to remain relatively stable. Additionally, we identified bacterial genera associated with maternal and infant-related factors.  Conclusions: These findings highlight the potential for targeted interventions aimed at modulating the breast milk microbiota to optimize the development of the newborn's intestinal microbiota.