The carbs in the mother's milk not only possess antibacterial properties of their own but also enhance the effectiveness of the antibacterial proteins also present.
‘Oligosaccharides in the human milk killed Group B Strep bacteria directly and also broke down the biofilms that the bacteria formed to protect themselves.’
"This is the first example of generalized, antimicrobial activity on the part of the carbohydrates in human milk," said 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."
New Tool To Fight Bacterial Resistance
The growing problem of bacterial resistance to antibiotics which causes 23,000 deaths annually, was the motivation for the research.
"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.
In a pilot study, Townsend's lab collected five samples. They found that the sugars from one sample nearly killed an entire strep colony. In another sample, the sugars were moderately effective while the remaining three samples exhibited a lower level of activity.
In a follow-up study, they are testing 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.
"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."
Sugar or Protein? Which Possess antimicrobial properties?
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.
The research team 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.
The compounds were added to strep cultures. They found that some of these oligosaccharides killed the bacteria directly and some also physically broke down the biofilms that the bacteria form to protect themselves.
"Our results show that these sugars have a one-two punch," said Townsend. "First, they sensitize the target bacteria and then they kill them. Biologists sometimes call 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 milk sugars and antimicrobial peptides from human saliva, the researchers also showed that the sugars' ability to break down biofilms can also enhance the effectiveness of the other antimicrobial agents that breast milk contains.
In follow-up studies the team has also shown that the milk sugars' antimicrobial activity extends to a number of other infectious bacteria, including two of the six "ESKAPE" pathogens that are the leading cause of hospital infections worldwide.
- Steven Townsend et al., Human Milk Oligosaccharides Exhibit Antimicrobial and Anti-Biofilm Properties Against Group B. Streptococcus, American Chemical Society 254th National Meeting & Exposition (2017).