Microbes and Microbiota: Benefits and Risks

Learnings in Conversation with Nursing Moms

Breastmilk is alive! This superfood includes essential nutrition for babies and their microbial partners in health. Learn more in dialogue with a medical microbiologist.


I love talking with nursing moms about the benefits of the breastmilk microbiota, natural microbes that are essential components of milk, a 200-million-year-old superfood! After a conversation with me about the breastmilk microbiota and its benefits to infants, a nursing mom who is not a scientist wanted to learn more. She posted a link to an article in Infection Control Today (ICT) about sugars in mother’s milk as a new class of antibacterial agents.

Photo by Leandro Cesar Santana on Unsplash

The article reported on research conducted at Vanderbilt University demonstrating that specific sugars (Human Milk Oligosaccharides or HMOs) provide multiple types of benefits to infants. The ICT article cited a published study by Ackerman et al. (2017), and this study was subsequently cited by Ackerman et al., (2018) and Le Doare et al. (2018). For those who want to learn more, some highlights of the work are provided below. All three studies are open access and can be downloaded for free at links in the reference section of this post for those who want to learn even more.

The mother’s genes (including those determining Lewis and Secretor status) encode HMOs. They are produced in mammary glands as a component of milk, yet HMOs are indigestible by infants! HMOs are recognized as prebiotics, nutrients not for baby, but for specific beneficial microbes in the infant gastrointestinal tract.

The studies of Ackerman and colleagues demonstrated that HMOs in milk from some donors directly kill a number of pathogens that cause gastrointestinal and respiratory infections in newborn infants and children. In addition to killing certain pathogens, the HMOs from other donors also disrupted pathogen attachment to host cells and formation of clusters of pathogenic bacteria in biofilms that can be resistant to antibiotics and host defenses. In some donors, HMOs neither killed nor disrupted biofilms of pathogens.

In addition to HMOs providing infants protection against certain pathogens, these same sugars shape the beneficial microbial communities colonizing the infant gut. Breastmilk supports hundreds of bacterial species at typical concentrations of ~1,000 bacteria per mL. Breastfed infants ingest nearly a million bacterial a day! The milk microbiota differs from the microbiota of other maternal niches, including the gut and the skin. Loss of the milk microbiota with pasteurization in human donor milk banks around the world caused loss of benefits to infants in multiple clinical studies. Future posts will address the diverse bacteria that make up the milk microbiota and their influence on development of healthy gut and immune systems in infants.

Key References

Ackerman, D. L., Doster, R. S., Weitkamp, J.-H., Aronoff, D. M., Gaddy, J. A., & Townsend, S. D. (2017). Human Milk Oligosaccharides Exhibit Antimicrobial and Anti-Biofilm Properties Against Group B Streptococcus. ACS Infectious Diseases, 3(8), 595–605.

Ackerman, D. L., Craft, K. M., Doster, R. S., Weitkamp, J.-H., Aronoff, D. M., Gaddy, J. A., & Townsend, S. D. (2018). Antimicrobial and Antibiofilm Activity of Human Milk Oligosaccharides against Streptococcus agalactiae, Staphylococcus aureus, and Acinetobacter baumannii. ACS Infectious Diseases, 4(3), 315–324.

Le Doare, K., Holder, B., Bassett, A., & Pannaraj, P. S. (2018). Mother’s Milk: A Purposeful Contribution to the Development of the Infant Microbiota and Immunity. Frontiers in Immunology, 9, 361.