Mothers of Preterm Infants Have Individualized Breast Milk Microbiota that Changes Temporally Based on Maternal Characteristics.

Mother's milk contains complex microbial communities thought to be important for colonizing a preterm infant's gastrointestinal tract. However, little is known about the microbiota in the preterm mother's milk and factors influencing its composition. We characterized the temporal dynamics of microbial communities in 490 breast milk samples from 86 mothers of preterm infants (born <1,250g) over the first 8 weeks postpartum. Highly individualized microbial communities were identified in each mother's milk that changed temporally with notable alterations in predicted microbial functions. However, pre-pregnancy BMI, delivery mode, and antibiotics were associated with changes in these microbial dynamics. Individual classes of antibiotics and their duration of exposure during prenatal and postpartum periods showed unique relationships with microbial taxa abundance and diversity in mother's milk. These results highlight the temporal complexity of the preterm mother's milk microbiota and its relationship with maternal characteristics as well as the importance of discussing antibiotic stewardship for mothers.