The human milk microbiota play an important role in mammary and infant health. However, there are limited data describing the composition and temporal variation in the milk microbiota beyond the first few months. Therefore, this study aimed to characterise the development of the human milk microbiota over the first two years postpartum and to investigate the factors that influence its composition. We performed full-length 16S rRNA gene sequencing on 608 samples collected from 86 mothers in the BLOSOM birth cohort. Similar to other populations, the milk microbiota of Western Australian women was low in diversity, and strongly dominated by Staphylococcus and Streptococcus species (14.95% and 39.04% relative abundance, respectively). Milk bacterial richness increased over time (p = 0.004), and there were significant changes in the abundances of 7 of 18 of the most abundant taxa over time. The composition of the milk microbiota was associated with numerous maternal and infant factors including infant age, maternal or infant antibiotic exposure, maternal probiotic use, parity, mode of delivery, and pre-pregnancy BMI (all p < 0.039). Our data provide new insights into how the human milk microbiota develop beyond the first few months and determinants of the milk’s bacterial composition, demonstrating that the milk microbiota are dynamic over time in the first two years postpartum.
Author Contributions
Conceptualisation, L.F.S., M.P.N. and D.T.G.; methodology, L.F.S.; formal analysis, R.X. and L.F.S.; investigation, R.X. and A.S.C.; resources, D.T.G.; data curation, R.X.; writing—original draft preparation, R.X.; writing—review and editing, L.F.S. and D.T.G.; visualisation, R.X.; supervision, L.F.S., D.T.G. and M.P.N.; funding acquisition, D.T.G. All authors have read and agreed to the published version of the manuscript.
Funding
This research is funded by an unrestricted research grant from Medela AG (Switzerland).
Institutional Review Board Statement
The study was conducted in accordance with the Declaration of Helsinki and approved by the Human Research Ethics Committee of The University of Western Australia (RA/4/20/4023).
Informed Consent Statement
Informed consent was obtained from all subjects involved in this study.
Data Availability Statement
Sequence data have been submitted to the NCBI SRA (BioProject Submission: SUB13951443).
Acknowledgments
The authors would like to acknowledge Erika van der Dries for collecting the samples and Matthew Payne for the use of his laboratory space and equipment.
Conflicts of Interest
D.T.G. declares their participation in the Scientific Advisory Board of Medela. AG. D.T.G. and L.F.S. receive funding from Medela AG administered through The University of Western Australia. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
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