Donor Human Milk Bacterial Microbiota Composition is Shaped by Breastfeeding Mode

Human milk contains a diverse community of microbes. The composition of this microbiota varies across different regions, and there is ongoing debate regarding its determinants.

To profile the bacterial composition of donor human milk samples from Shanghai, China, and to explore the factors influencing its composition.

A cross-sectional study was conducted from February 2018 to July 2022, involving 252 participants from the Shanghai Donor Human Milk Bank, Shanghai Children's Hospital. 16S rRNA sequencing was performed, and the microbiota composition was analyzed using K-means clustering, multiple linear regression, and sparse estimation of correlations among microbiomes.

The majority of detected taxa belonged to the phyla Firmicutes, Proteobacteria, Bacteroidota, and Actinobacteriota. Four clusters enriched with Staphylococcus, Staphylococcus and Achromobacter, Achromobacter, Streptococcus, Streptococcus, and Acinetobacter were identified. Multivariable linear regression showed that at least some indirect breastfeeding was independently associated with lower bacterial diversity. Also, at least some indirect breastfeeding, preterm birth, and Cesarean section were associated with a higher relative abundance of Staphylococcus. Higher milk protein content was linked to increased levels of Lactobacillus and Enterococcus, while lactation stage at sample collection inversely related to these genera. More linear and nonlinear relationships among the predominant genera of the direct breastfeeding group were found compared to the indirect breastfeeding group.

Breastfeeding mode was identified as a pivotal determinant of human milk microbial composition. Investigation of the milk microbiota composition may provide clues for optimizing donor human milk collection, processing, and utilization practices.