Abstract
Breastfeeding protects against diseases, with potential mechanisms driving this being human milk oligosaccharides (HMOs) and the seeding of milk-associated bacteria in the infant gut. In a cohort of 34 mother–infant dyads we analyzed the microbiota and HMO profiles in breast milk samples and infant’s feces. The microbiota in foremilk and hindmilk samples of breast milk was compositionally similar, however hindmilk had higher bacterial load and absolute abundance of oral-associated bacteria, but a lower absolute abundance of skin-associated Staphylococcus spp. The microbial communities within both milk and infant’s feces changed significantly over the lactation period. On average 33% and 23% of the bacterial taxa detected in infant’s feces were shared with the corresponding mother’s milk at 5 and 9 months of age, respectively, with Streptococcus, Veillonella and Bifidobacterium spp. among the most frequently shared. The predominant HMOs in feces associated with the infant’s fecal microbiota, and the dominating infant species B. longum ssp. infantis and B. bifidum correlated inversely with HMOs. Our results show that breast milk microbiota changes over time and within a feeding session, likely due to transfer of infant oral bacteria during breastfeeding and suggest that milk-associated bacteria and HMOs direct the assembly of the infant gut microbiota.
Highlights
Study participant characteristics bacteria We found no significant differences in maternal foremilk or Mother–infant dyads included in this study were enrolled as participants in the SKOT III cohort, including two groups of infants hindmilk between infants experiencing EWG and normal weight gain (NWG) in terms of bacterial load or composition (Fig. S3)
When calculating absolute abundances we found that most collected at infant age 5 and 9 months, as well as blank DNA bacterial genera, notably many of which are often found as extraction controls (Fig. 1a)
At infant age 5 months (Fig. 4d and Fig. S5d), we found that sharing of various Streptococcus amplicon sequence variant (ASV) (e.g., S. mitis group, S. salivarius, S. perorsis and S. lactarius) was highly prevalent (>80% of mother–infant pairs)
Summary
Breastfeeding reduces the risk of infectious diseases and may reduce the risk of obesity, metabolic, and immunerelated diseases later in life.[1,2] Breast milk contains all the macroand micronutrients necessary for infant growth, as well as bioactive compounds such as antimicrobial compounds, immunoglobulins, cytokines, peptide hormones and growth factors.[3,4]research within the last decade has revealed that breast milk contains a diverse microbiota,[5,6,7,8] which may act as a reservoir of microbes for colonization of the infant gut and subsequently impact current and long-term health.[9,10,11] The origins of bacteria in human breast milk are not fully elucidated but thought to be maternal skin,[12] infant oral cavity[13] and environmental,[7] as well as the maternal gut and oral cavity through the proposed entero-mammary[14] and oro-mammary pathways,[15] respectively. To our knowledge, no previous studies have assessed how the bacterial load and composition changes along a feeding session. It has been estimated that exclusively breastfed infants, by consuming ~800 ml breast milk per day, ingest somewhere between 105 and 107 bacteria daily through breast milk.[10] knowledge on which milk-associated bacterial taxa that establish and colonize the infant gut is scarce, and only a limited number of studies have estimated the extent to which breast milk microbes are transferred to the infant gut longitudinally.[13,19,20] Especially, information about potential continued milk-to-gut transmission of bacteria spanning the complementary feeding period is lacking
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