People long believed that breast milk was sterile - and bacteria were considered contaminants. Now we know better. Mother's milk contains an amazing range of bacteria, forming a microbiome unique to breast milk.

In the review, Breast Milk, a Source of Beneficial Microbes and Associated Benefits for Infant Health, published in 2020, experts report on almost 300 studies into this microbiome. It's a healthy reminder of the benefits of breastfeeding - and reinforces the fact that there is so much more we can learn about mother's milk.

Bacteria and baby's gut

In the past years, science has been investigating the beneficial effects of the commensal and probiotic bacteria in mother's milk - especially as it affects baby's gut health. Though it is difficult to grow cultures of some bacteria, researchers have been able to identify several hundred species of bacteria in breast milk.

Once they enter baby's gut, the commensal bacteria in breast milk work together to force out pathogens, by competing with them for nutrients. They also produce anti-microbial compounds, prevent pathogens from adhering to the intestinal lining and stimulate intestinal mucin production.

Lactobacillus species in mother's milk - a potential probiotic - have the power to prevent bacteria from adhering to intestines, helping prevent babies from developing such infections as Shigella, Salmonella and E. coli.

Feeding all that good bacteria in baby's intestinal microbiome is the job of over 200 different types of human milk oligosaccharides (HMOs), which are components that infants are unable to digest. HMOs not only work as prebiotics, they also fight infection by blocking pathogens from adhering to the intestinal lining. HMOs may even play a key role in preventing respiratory infections.