Human breast milk contains many known antimicrobial and immunomodulatory molecules, including immunoglobulins, antimicrobial peptides, and fatty acids. In a study published 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 aureusBacillus subtilisClostridium perfringensEscherichia coli), human milk was more antimicrobial than cows’ milk and infant formula.

“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.”

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.”

Now, the above photo, posted by a biology student in England, features nine Petri dishes completely colonised with the bacteria M. Luteus, except in the center, where tiny puddles of breast milk have created what looks like “moats” of protection around themselves.⁣⁣

The student, Vicky Green, said she had similar results with Petri dishes full of e.Coli and the dreaded anti-biotic resistant “super bug” MRSA.⁣⁣ ⁣

“The white spots in the middle are discs soaked in two samples of breastmilk,” Green wrote in the caption of her post. “See the clear bit around the discs ― that’s where the proteins in the milk have inhibited the bacteria!”⁣⁣

An article from explains how this is possible:⁣⁣

“About 80 percent of the cells in breast milk are macrophages, cells that kill bacteria, fungi and viruses. Breast-fed babies are protected, in varying degrees, from a number of illnesses, including pneumonia, botulism, bronchitis, staphylococcal infections, influenza, ear infections, and German measles. Furthermore, mothers produce antibodies to whatever disease is present in their environment, making their milk custom-designed to fight the diseases their babies are exposed to as well.”⁣