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Study: Human Milk Contains Powerful Antimicrobial Compound

Human breast milk contains many known antimicrobial and immunomodulatory molecules, including immunoglobulins, antimicrobial peptides, and fatty acids. In a study published today in the journal Scientific Reports, researchers investigated a small molecule called glycerol monolaurate (GML) in human milk versus cows’ milk and infant formula for antimicrobial and antiinflammatory activities: human milk contained 3,000 µg/ml of GML, compared to 150 μg/ml in cows’ milk and none in infant formula; for bacteria tested (Staphylococcus aureus, Bacillus subtilis, Clostridium perfringens, Escherichia coli), human milk was more antimicrobial than cows’ milk and infant formula.

Study: Human Milk Contains Powerful Antimicrobial Compound
Human breast milk. Image credit: Amada44 / CC BY-SA 3.0.

“Our findings demonstrate that high levels of GML are unique to human milk and strongly inhibit growth of pathogenic bacteria,” said National Jewish Health’s Professor Donald Leung, senior author of the study.

“While antibiotics can fight bacterial infections in infants, they kill the beneficial bacteria along with the pathogenic ones,” added University of Iowa’s Professor Patrick Schlievert, first author of the study.

“GML is much more selective, fighting only the pathogenic bacteria while allowing beneficial species to thrive.”

“We think GML holds great promise as a potential additive to cows’ milk and infant formula that could promote the health of babies around the world.”

After determining that human milk contains much higher levels of GML than does cows’ milk, the researchers showed that human milk inhibits the growth of Staphylococcus aureus, Bacillus subtilis, Clostridium perfringens, and Escherichia coli, while neither cows’ milk nor infant formula had any effect.

Furthermore, human milk did not inhibit the growth of the beneficial bacteria Enterococcus faecilis.

When the study authors removed GML from human milk, it lost its antimicrobial activity against Staphylococcus aureus. When they added GML to cows’ milk, it became antimicrobial.

They also showed that GML inhibits inflammation in epithelial cells, which line the gut and other mucosal surfaces. Inflammation can damage epithelial cells and contribute to susceptibility to both bacterial and viral infections.

“Collectively, our study suggests that there are great benefits to human milk compared to cows’ milk and formula,” they said.

“Positive effects of human milk appear to be due in part to the presence of GML combined with other known and unknown factors.”

“Future studies are needed to determine whether or not supplementation of cows’ milk and commercial infant formula with GML will be beneficial.”


Patrick M. Schlievert et al. 2019. Glycerol Monolaurate Contributes to the Antimicrobial and Anti-inflammatory Activity of Human Milk. Scientific Reports 9, article number: 14550; doi: 10.1038/s41598-019-51130-y

Topic: #breast milk
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