Breastmilk is no longer considered a sterile fluid, as was once thought. Breastfeeding provides a niche of microbes to baby’s gut.
O’Hara and co-workers1 observe that “gut microbes have a collective metabolic activity equal to a virtual organ within an organ”, and refer to the gut flora as “a forgotten organ”.
Metagenomics, a swiftly evolving microbial science, offers an exceptional window to the microbial biosphere in breastmilk. Ward and colleagues2 found bacterial communities in breastmilk with over 360 prokaryotic genera (basic unicellular organisms).
Bacteria, viruses, fungi and others, and their genetics form the “milk microbiome”, providing amazing insights to nutritional science. Microbes in milk have been found and investigated with studies conducted in humans, and other mammals. Oikonomou and colleagues3 compare milk microbiota in different species and suggest that a core milk microbiome may exist across the board. This provides basis for motivational concepts of therapy and therapeutics.
The immature gut of the newborn needs much maternal guidance for development of a robust ecological environment to survive and adapt in an unpredictable world. Philosophically, one may perceive that a mother mandates to tutor the young one all lessons that she has learnt the hard way, making it as cost-effective as possible. She attempts to completely prevent diseases in her young rather than to merely reduce the pain of diseases. She provides a vaccination of sorts through physical and emotional bonding by breastfeeding, replete with her microbes.
Gut microbial profiles are in fact different in breastfed infants and non-breastfed infants. Heikkilä and colleagues4 find that a baby breastfeeding approximately 800 mL of milk a day would ingest somewhere between 8 × 104 and 8 × 106 bacteria (commensal) while suckling.
It is yet unclear why or how a number of important factors impact microbial nature and diversity. Both colostrum and mature milk provide diverse microbes to the baby’s gut. Maternal breastfeeding practices, diet, genetics, maternal health and body mass index, mode of delivery, and preterm deliveries, antibiotic usage during delivery 5and so on, all influence them. Inter- individual and inter-cultural variations and differences in geographic locations6 also could contribute to microbial variability.
Origins and functions of breastmilk microbes
Notwithstanding knowledge of the exact origin of breastmilk microbes, mum and baby shared microbes even as early as when baby was in utero. Microbes continue to bond them through breastfeeding for a profound purpose, as bedrock for health of body and brain.
Microbes in the infant’s gut are related to mother’s milk and skin, enhanced by early skin-to skin contact. Flow from the mouth of the baby back into the breasts can occur during suckling, as another possible source of milk microbes.
Moossavi and colleagues7 observe that nursing directly at the breast versus pumping and feeding breastmilk from a bottle is associated with differences in microbes, suggesting that direct breastfeeding is important, because it introduces microbes into milk, by suckling. However, the puzzle isn’t solved because milk secreted by some women before delivery (precolostrum) already contains microbes.
Milk microbes travel from mother’s gut
A lactating mother’s breasts, by being a part of a more extensive mucosal immune system, remain in cognizance of early immune “information” from mucosal surfaces of the body, which lead early combat against microbes that attempt entry into the body. Through routes of communication, the mother can transfer microbial “signals’’ into her milk. Antibodies, suckled in milk, insulate baby’s gut mucosae from the attachment of harmful microbes, learning from mum’s own experience as she would have encountered and defended against them in her own gut.
A link between a mother’s gut and her breasts8 during late pregnancy and throughout lactation possibly exists. She provides a vaccination of sorts through possible gut-to-breast links. Some microbes may leave her gut, in free living state or in association with immune cells, and travel to her breasts. Beneficial microbes enter her milk, and some possibly communicate useful immune information to the breastfed baby.
Breastmilk microbes can colonise the mucosal surfaces of the baby’s gut as a shield against gut and blood infections. Microbes help mature and strengthen immature gut barriers and steer immune systems for optimal development through immune modulators in milk itself.
They protect from diarrheas, respiratory conditions, and health challenges faced by an immature immune system, tangibly reducing infant and childhood morbidities and mortalities.
Disease protection and immune functions
Strong fundamentals of health in the first 100 days of life potentially empower us with sound physical and mental well- being, and if other factors are moderated, such effects could endure for the rest of our lives.
Through cellular signals, microbes offer useful insights to the developing immune system for survival and adaptation. A spectrum of diseases associated with immune imbalances such as allergies, diabetes mellitus, autoimmune diseases and obesity are reduced in breastfed infants, at least in part, through the actions of beneficial gut microbes, received, as an early nidus to good health, through mum’s immune heritage.
Dr Prameela Kannan Kutty is Professor of Paediatrics at Universiti Pertahanan Nasional Malaysia
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