Streptococcus agalactiae (Group B-Streptococcus, or GBS) is a type of bacteria that can cause invasive infections in people of all ages. A research team led by Vanderbilt University scientists has found that although GBS bacteria can be transmitted to infants through breastfeeding, some mothers produce complex sugars, also called oligosaccharides, in their milk that could help prevent infection. The team also reports that these sugars can act as anti-biofilm agents.
This illustration depicts a 3D computer-generated image of a group of clindamycin-resistant GBS bacteria, which were arranged in chains. The artistic recreation was based upon scanning electron microscopic (SEM) imagery. If you look carefully, you’ll be able to see a number of these organisms undergoing the process of cell division along the long axis of their respective chains. Image credit: James Archer / CDC.
“We started to look for different methods to defeat infectious bacteria. For inspiration, we turned to one particular bacteria, GBS,” said lead author Dr. Steven Townsend, assistant professor of chemistry at Vanderbilt University.
“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.”
GBS infections in newborns less than a week old can be prevented. If a pregnant woman tests positive for GBS during her last trimester, she can take antibiotics during labor to significantly reduce the risk that her baby will become sick at birth. This has been an effective prophylactic strategy for early-onset disease in the first week of life. But sometimes an infection can take hold later, between one week and three months after infants are born.
Curious as to how GBS was infecting these young infants in the first place, scientists about a decade ago found cases in which the bacteria were transmitted through breast milk, despite milk’s known immunologic benefits.
But because most babies do not become infected with GBS, Dr. Townsend and co-authors wanted to see if some women’s breast milk contained protective compounds that specifically fight that bacteria.
“As carbohydrate chemists, we knew from previous research that milk carbohydrates are protective against other bacteria, so we figured there would be a chance they would be active against GBS, too,” Dr. Townsend said.
To test their hypothesis, the researchers collected human milk 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.
In a pilot study, the authors 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.
“When bacteria want to harm us, they produce this gooey protective substance called a biofilm, which allows them to thwart our defense mechanisms,” Dr. Townsend said.
“In the initial study, the sugars from one mother’s milk killed nearly the entire colony. Another milk sample was moderately effective, while the remaining three showed diminished activity.”
In a follow-up study, the team is testing more than two dozen additional samples.
So far, two samples have shown activity against both bacteria and biofilms; two just worked against bacteria but not biofilms; and four helped fight biofilm formation but not bacteria. Six were relatively inactive against both.
“Preliminary data also suggest that some mothers produce milk sugars that make the bacteria more susceptible to common antibiotics, including penicillin and erythromycin,” Dr. Townsend said.
“If these results bear out through future studies, these sugars could potentially become a part of an antibacterial treatment for infants or adults. They could also help reduce our dependence on some common antibiotics.”
“The great thing about these sugars is that if they’re safe for babies, they should be safe for everyone,” he said.
The results are published in the journal ACS Infectious Diseases.
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Dorothy L. Ackerman et al. 2017. Human Milk Oligosaccharides Exhibit Antimicrobial and Antibiofilm Properties against Group B Streptococcus. ACS Infect. Dis 3 (8): 595-605; doi: 10.1021/acsinfecdis.7b00064
