Turns out, sugars in breastmilk keep bacteria at bay

Mother's milk, which consists of a complex and continually changing blend of proteins, fats and sugars, helps protect babies against bacterial infections.

In the past, scientists have concentrated their search for the source of its antibacterial properties on the proteins it contains. However, an interdisciplinary team of chemists and doctors at Vanderbilt University discovered that some of the carbohydrates in human milk not only possess antibacterial properties of their own but also enhance the effectiveness of the antibacterial proteins also present.

"This is the first example of generalized, antimicrobial activity on the part of the carbohydrates in human milk," said study director Steven Townsend. "One of the remarkable properties of these compounds is that they are clearly non-toxic, unlike most antibiotics."

The basic motivation for the research was the growing problem of bacterial resistance to antibiotics, which the Center for Disease Control and Prevention estimates causes 23,000 deaths annually.

"We started to look for different methods to defeat infectious bacteria. For inspiration, we turned to one particular bacteria, Group B Strep. We wondered whether its common host, pregnant women, produces compounds that can either weaken or kill strep, which is a leading cause of infections in newborns worldwide," Townsend said.

Instead of searching for proteins in human milk with antimicrobial properties, Townsend and his colleagues turned their attention to the sugars, which are considerably more difficult to study.

"For most of the last century, biochemists have argued that proteins are most important and sugars are an afterthought. Most people have bought into that argument, even though there's no data to support it," Townsend said. "Far less is known about the function of sugars and, as a trained glycoprotein chemist, I wanted to explore their role."

To do so, the researchers collected human milk carbohydrates, also called oligosaccharides, from a number of different donor samples and profiled them with a mass spectrometry technique that can identify thousands of large biomolecules simultaneously. Then they added the compounds to strep cultures and observed the result under the microscope. This showed that not only do some of these oligosaccharides kill the bacteria directly but some also physically break down the biofilms that the bacteria form to protect themselves.

The study is published in the ACS Infectious Diseases journal.