Maple compound offers natural protection against cavities

A new study in the journal Microbiology Spectrum highlights the potential of using a natural compound from maple to combat the bacteria responsible for tooth decay: Streptococcus mutans. The compound, epicatechin gallate, is a powerful and safe alternative to traditional plaque-fighting agents. Its natural abundance, affordability and lack of toxicity make it especially promising for inclusion in oral care products such as mouthwashes, offering a safer option for young children, who often accidentally swallow mouthwash.

The new study emerged as an offshoot of research into natural compounds that inhibit biofilm formation in Listeria monocytogenes, a foodborne pathogen. As is often the case in science, the researchers made an unexpected observation that Listeria readily forms biofilms on plant materials, including most wood, but seems to avoid certain types, especially maple. This piqued the researchers' curiosity. They isolated polyphenolic compounds from maple that inhibit Listeria attachment and biofilm formation. They also identified their target: sortase A, an enzyme that anchors adhesins to the bacterial cell wall. When sortase A is inhibited, these adhesins are not anchored in the bacterial cell wall, impairing the ability of Listeria to attach to surfaces and form biofilms. That discovery led the researchers to investigate whether similar mechanisms exist in related bacteria. Sortase A in Streptococcus species, which is Listeria's cousin in the Bacillota phylum, turned out to be quite similar. One species in particular, Streptococcus mutans, stood out because it causes dental caries, commonly known as cavities. 

Since S. mutans initiates cavities by forming biofilms (plaques) on teeth and producing acid that destroys tooth enamel, we asked: could maple polyphenols also inhibit S. mutans biofilms? That question drove this study."

Mark Gomelsky, Ph.D., corresponding study author, Martha Gilliam Professor of Microbiology and Director of the Microbiology Program, University of Wyoming

The researchers first used computer modeling to see whether maple polyphenols could bind to the sortase A enzyme from S. mutans, and discovered that they did. Next, they purified the sortase A in the lab and confirmed that these compounds inhibit its activity in a test tube. Finally, they assessed whether maple polyphenols block S. mutans from forming biofilms on plastic teeth and on hydroxyapatite disks-a stand-in for real tooth enamel- and discovered they worked there too. 

"In a way, this study felt almost too easy. Everything fell into place just as we predicted. That's a rare experience in science, and probably the first time it's happened in my 35-year research career," Gomelsky said. "We discovered that several polyphenols present in maple wood or maple sap can inhibit the sortase enzyme in S. mutans, which in turn prevents this cavity-causing bacterium from attaching to tooth surfaces." Interestingly, the most potent inhibitor was (-)-epicatechin gallate (ECG), a compound also present in green and black tea, though in much higher amounts in tea than in maple sap. Drinking green tea has long been associated with lower rates of cavities, and its main polyphenol, (-)-epigallocatechin gallate (EGCG), has been used in dental products. The researchers found that EGCG does inhibit S. mutans biofilms, but it's not nearly as effective as ECG. This raises the intriguing possibility that the moderate effects seen with EGCG-based dental products may be due to using the suboptimal compound, instead of the more potent ECG.

"Our findings suggest that ECG or other edible polyphenols with anti-sortase activity could be added to dental products to help prevent cavities through an antibiofilm mechanism," Gomelsky said. "This is different from traditional approaches, which rely on killing bacteria with alcohol, disinfectants or essential oils, or on fluoride to remineralize enamel. The antibiofilm approach using edible polyphenols is especially appealing for young children. For example, young children can't use conventional mouthwashes because they might swallow them and risk toxicity. A safer alternative, such as a mouthwash containing an effective dose of an edible polyphenol, could provide protection without harmful side effects."

Gomelsky said they are actively developing plant polyphenol-based dental products through a startup founded by University of Wyoming students and the first author of this study, Ahmed Elbakush, Ph.D.