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NEW Research: Antibiotics affect milk microbiota in mothers of preterm infants

Updated: Jun 8


Led researcher, PhD Candidate Michelle Asbury
Michelle Asbury

Our newest research led by PhD Candidate, Michelle Asbury, has found that mothers of preterm babies have highly individual breast milk microbiomes and that even short courses of antibiotics have prolonged effects on the diversity and abundance of microbes in their milk.



Did you know that Breast Milk has Microbes? Microbes are microscopic organisms including bacteria, fungi and more! Microbes in breast milk come from mother's skin, mother's gut, breast tissue, breast pump etc. Microbes are important as they can help protect the baby from disease and support healthy development.

Study Highlights


Using milk samples provided by 86 mothers participating in the OptiMoM Fortifier Study from the first eight weeks after delivery, we found:

  • Mothers of preterm infants have individualized microbiota in their breast milk

  • The microbiota of preterm milk changes over time

  • Maternal BMI and delivery mode are related to preterm milk microbiota over time

  • Preterm milk microbiota differs with maternal antibiotics (class, timing, and duration)


Study Details


The study is the largest to date of breast milk microbiota in mothers of preterm infants, and it is the first to show that antibiotic class, timing and duration of exposure have particular effects on the most common microbes in breast milk — many of which play a role in fostering disease, or in gut health and metabolic processes that promote babies’ growth and development.


86 mothers provided 490 breast milk samples from weeks 1-8 of life. We found that mothers have unique microbiota express in their breast milk, microbiota in preterm breastmilk changes over time. Maternal factors including body mass index, mode of delivery and antibiotic usage influence microbial changes in preterm breastmilk during an infant's hospitalization.
Study Highlights. Taken from: Asbury et al., 2020, Cell Host & Microbe

Asbury says it is too early to know what the findings mean for preterm infant health and outcomes. She and other members of our team will dive into those questions over the next year, as they compare their findings with stool samples from the preterm infants involved in the study. Stay tuned to hear more about whether changes in the mothers’ milk microbiomes are actually seeding the infants’ guts to promote health or increase disease risk!


Meanwhile, it’s important that mothers with preterm infants continue to take antibiotics for some cases of mastitis, blood infections and early rupture of membranes. Roughly 60 percent of women in the current study took antibiotics — highlighting both the vast need for these drugs and the potential for some overuse.


“It came as quite a shock to us that even one day of antibiotics was associated with profound changes in the microbiota of breast milk”, says Dr. Deborah O’Connor. “I think the take-home is that while antibiotics are often an essential treatment for mothers of preterm infants, clinicians and patients should be judicious in their use.”


Dr. Sharon Unger says that the benefits of breastfeeding far outweigh the risk that antibiotics can disrupt the breast milk microbiome and that mothers should without question continue to provide their own milk when possible. “But I think we can look to narrow the spectrum of antibiotics we use and to shorten the duration when possible,” Unger says. She adds that advances in technology may allow for quicker diagnoses of infection and better antibiotic stewardship in the future.


The study was published in the journal of Cell Host & Microbe in September 2020.

© 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/


This blog post has been adapted from an article originally posted on sickkids.ca on September 4, 2020.