Abstract
ABSTRACTMicrobes are present in human milk regardless of the mother's health. The origins of the milk microbiota likely include the mother's skin, infant's mouth, and transfer from the maternal gastrointestinal (GI) tract. Prominent bacterial taxa in human milk are Staphylococcus and Streptococcus, but many other genera are also found including anaerobic Lactobacillus, Bifidobacterium, and Bacteroides. The milk microbiome is highly variable and potentially influenced by geographic location, delivery mode, time postpartum, feeding mode, social networks, environment, maternal diet, and milk composition. Mastitis alters the milk microbiome, and the intake of Lactobacilli has shown potential for mastitis treatment and prevention. Although milk and infant fecal microbiomes are different, their variations appear to be related – suggesting that milk is an important contributor of early GI colonization. Nonetheless, nothing is known regarding whether the milk microbiome influences infant health. Further research and clinical interventions are needed to determine if changes in the microbiomes of human milk and infant formula/food impact health.
Highlights
The maternal microbiome has long been recognized as one of the essential factors determining the neonatal microbiome
This finding is supported by recently published data from the Canadian Healthy Infant Longitudinal Development (CHILD) cohort, which evaluated human milk samples produced by 393 mainly Caucasian mothers; overall, the most abundant taxa were identified as variants of Streptococcus (16%) and the third most abundant were variants of Staphylococcus (5%) [28]
Identification of these strains in the milk of the mothers provides additional evidence for translocation of microbes from the intestine to the mammary gland [47,48,49]. These findings strongly suggest that, in addition to those bacteria that can be considered to be derived from the skin or the infant’s mouth, human milk likely contains bacteria that are translocated from the maternal GI tract to the mammary gland (Figure 1)
Summary
The maternal microbiome has long been recognized as one of the essential factors determining the neonatal microbiome. Based on the demonstrated advantages of being breastfed (or fed human milk by other means), the microbiome of the healthy, vaginally delivered infant can be considered the “reference standard,” generally providing the best chance for optimal development of the offspring’s immune system and metabolism. The infant’s GI microbiome is extensively linked with the immune system, and understanding what is a “normal, healthy” infant GI microbiome in a distinct population could provide opportunities to improve the health of both breastfed and formula-fed infants in that population This requires indepth understanding of the basic principles, including the microbial ecosystems during the perinatal period and its associations with human milk composition including the human milk microbiome. Since these microbes and their antigens are some of the first experienced by the immature infant’s immune system, it is likely that they play an important role in an infant’s immune development, including factors related to establishing tolerance to generally nonpathogenic microbes common in the infant’s environment
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