Human Milk Compound Selectively Fights Harmful Bacteria

Researchers have identified a compound in human breast milk—glycerol monolaurate (GML)—that fights infection by harmful bacteria while allowing beneficial bacteria to thrive. Human breast milk has more than 200 times the amount of GML than cow milk, and infant formula has none. Given that GML is inexpensive to manufacture, it could potentially be added to cow milk and infant formula. Future research will whether this could be beneficial.

“Our findings demonstrate that high levels of GML are unique to human breast milk and strongly inhibit growth of pathogenic bacteria,” says senior author Donald Leung of National Jewish Health. The findings were published today in Scientific Reports.

“While antibiotics can fight bacterial infections in infants, they kill the beneficial bacteria along with the pathogenic ones,” explains first author Patrick Schlievert of the University of Iowa. “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 cow’s milk and infant formula that could promote the health of babies around the world.”

After determining that human breast milk contains much higher levels of GML than does cow milk, the researchers showed that human breast milk inhibits the growth of the pathogenic bacteria Staphylococcus aureus, Bacillus subtilis, and Clostridium perfringens, while neither cow milk nor infant formula had any effect. However, human breast milk did not inhibit the growth of the beneficial bacteria Enterococcus faecilis. Babies fed on human breast milk also have high levels of beneficial bifidobacteria, lactobacilli, and other enterococci bacteria.

When researchers removed the GML from human breast milk, it lost its antimicrobial activity. And when they added GML to cow milk, it became antimicrobial. Additionally, the researchers showed that GML inhibits inflammation—which can damage epithelial cells and contribute to susceptibility to infection—in epithelial cells. Because of this, the researchers have applied for a patent for the use of GML as a beneficial additive to cow milk and infant formula.