The Relationship Between Abnormal Metabolic Status and the Breastmilk Microbiome in Women Three Months Post‐Partum

Background The gastrointestinal (gut) microbiome established during infancy plays an important role in the maturation of the gastrointestinal tract and immune system. In addition, a growing body of evidence suggests gut microbial community composition may impact short‐ and long‐term health. Breastmilk contains a vast array of microbes and is believed to play a role in early colonization of the infant gut. Maternal metabolic status and infant mode of delivery have been suggested to influence the microbial milieu of breastmilk, however, systematic investigation of these associations is required. The objective of this study was to determine if maternal gestational diabetes mellitus (GDM), impaired glucose tolerance (IGT), or mode of delivery (scheduled caesarean delivery [C‐section], unscheduled C‐section, vaginal delivery) impacts the microbial composition of breastmilk. Methods Metagenomic DNA extraction and 16S gene sequencing of the rDNA V4 hypervariable region was carried out on breastmilk to determine microbial composition. Breastmilk samples were obtained from complete breastmilk expressions at three months post‐partum from otherwise healthy women who delivered term‐born infants (n= 116). Results Principal coordinate analysis of Bray‐Curtis dissimilarity did not reveal clustering of the different groups (non‐GDM versus GDM; non‐GDM versus IGT versus GDM; scheduled C‐section versus unscheduled C‐section versus vaginal delivery; total C‐section versus vaginal delivery). In addition, no major differences in alpha diversity were found between the GDM status groups or delivery method groups using the Chao1 index. Proteobacteria and Firmicutes were found to be the predominant phyla in the breastmilk sample. Genus level analyses revealed high abundance of Pseudomonas and Streptococcus genera regardless of maternal metabolic status or mode of delivery. Low levels of Staphylococcus , Veillonella and Acinetobacter were also found among all of the groups. Significance These findings may indicate that the microbiome of mature breastmilk at three months post‐partum may be resistant to perturbation by maternal metabolic abnormalities and mode of delivery. Thus, breastmilk may play an important role in mitigating the effects of other factors that negatively affect colonization of the infant gut. Further research in this area is warranted. Support or Funding Information Canadian Institutes of Health Research, Canadian Diabetes Association