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Mother’s Milk: Sugars Are New Class of Antibacterial Agents

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Mother’s milk, contains a complex and continually changing blend of proteins, fats and sugars, helps shield babies against bacterial infections.

Why is mother's milk valuable?

In the past, scientists have focused their search for the source of its antibacterial properties on the proteins it contains. Though, an interdisciplinary team of chemists and doctors at Vanderbilt University have discovered that some of the carbohydrates in mother's milk not only have antibacterial properties of their own but also improve 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.” This said by Assistant Professor of Chemistry Steven Townsend, who directed the study. “One of the remarkable properties of these compounds is that they are clearly non-toxic, unlike most antibiotics.”

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

Instead of searching for proteins in mother's milk with antimicrobial properties, Townsend and his colleagues turned their attention to sugars. Focusing in sugars 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 trained glycoprotein chemist, I wanted to explore their role.”

To do so, the researchers collected mother's milk carbohydrates, also called oligosaccharides, from a number of different donor samples. Then, they profiled them with a mass spectrometry technique that can classify thousands of large biomolecules instantaneously. Then they added the compounds to strep cultures and perceived the result under the microscope. This displayed that some of these oligosaccharides kill the bacteria directly. But some also physically break down the biofilms that the bacteria form to shield themselves.

In a pilot study, Townsend’s lab collected five samples. They found that the sugars from one sample approximately killed a total strep colony. In another sample, the sugars were discreetly effective while the remaining three samples displayed a lower level of activity. In a follow-up study, they are analyzing more than two dozen additional samples. So far, two broke down the bacterial biofilms and killed the bacteria. Four broke down the biofilms but did not kill the bacteria. And two killed the bacteria without breaking down the biofilms.

“Our results show that these sugars have a one-two punch,” said Townsend. “First, they sensitize the target bacteria and then they kill them. Biologist sometimes calls this ‘synthetic lethality’ and there is a major push to develop new antimicrobial drugs with this capability.”

By dosing strep cultures with a mixture of mother's milk sugars and antimicrobial peptides from human saliva, the researchers also exhibited that the sugars’ ability to break down biofilms can also improve the effectiveness of the other antimicrobial agents that mother's milk contains.

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