Brushing your teeth: no longer the best thing for your teeth
Here’s an article, via MicrobeWorld, that details very recent work published in Applied and Environmental Microbiology. The paper examines commensal microorganisms in the mouth, and the relative role they play in the formation of dental plaque. As we are probably well aware, the oral cavity is home to a vast number of microorganisms, a collection of prokaryotic and eukaryotic species. One bacterial species, Streptococcus mutans, is responsible for the process of tooth decay. S. mutans is a potent biofilm forming microorganism, and the presence of sucrose (table sugar) promotes the formation of the biofilm. When S. mutans acquires other sugars such as glucose and fructose, the growth of the organism produces lactic acid when it metabolizes the sugar. The acid produced as it grows causes the enamel of the teeth to be degraded. The combination of adhesion via plaque formation and acid production lead to the process of tooth decay, and the mechanical removal of plaque by brushing continues to be the most effective method for preventing dental caries.
This new report from the National Institute of Infectious Diseases, Tokyo details another common microorganism from the oral cavity, Streptococcus salivarius, which actually does not form biofilms. When the scientists added S. salivarius to a biofilm formation assay in the laboratory, they found that this bacterium actually inhibited the formation of biofilms. Two enzymes made by the bacterium appear to be responsible for the phenomenon. Both of the enzymes are enzymes that modify sugars present in the environment: fructosyltransferase (FTF) and exo-beta-D-fructosidase (FruA,) and FruA became elevated in the presence of sucrose, the sugar that promotes the ability of plaque bacteria to form biofilms. FruA had actually previously been studied and purified from a fungal source, and addition of that fungal enzyme into the laboratory biofilm formation assay also inhibited biofilm formation.
The conclusion of the research suggests that organisms in the mouth are interacting and competing for nutrients. S. mutans, for instance, works to acquire sucrose for incorporation into plaque, giving it an advantage to remain in the mouth under the flushing influence of saliva. S. salivarius, is also working to acquire sugars, but must compete with S. mutans for that resource. So in order to compete, it promotes the loss of the biofilm, likely leading to the loss of S. mutans from the oral cavity.
This research does offer a possible approach for combating tooth decay. One can look for a way to promote the growth of the biofilm-inhibiting bacteria, or add prophylactic enzyme in a mouthwash or other delivery mechanism. I think that this research really does shed some light on why some individuals are more resistant to dental caries than others: their normal oral microbial flora may be dominated by biofilm-inhibitors than biofilm-promoters. So let’s look into oral microbe transplants for everyone, and throw away our toothbrushes!
BONUS: Can you describe a wrinkle in my rosy scenario above?