Brushing your teeth: no longer the best thing for your teeth

Streptococcus mutans. Gram stain. Thioglycolla...

Gram stained S. mutans, Image via Wikipedia

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?

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About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on March 24, 2011, in Bonus!, Microbes in the News, Strange but True. Bookmark the permalink. 6 Comments.

  1. Steph Weakland

    S. salivarius does combat the formation of biofilms, but that is not the only threat posed by S. mutans. S. mutans does form biofilms in the presence of sucrose, but it further affects dental health in the presence of other sugars. As it acquires and metabolizes glucose and fructose, S. mutans produces dangerous lactic acid that leads to degradation of tooth enamel. Therefore, using S. salivarius to hinder the formation of biofilms will not resolve all aspects of the problem.

    • Hopefully the tendency of S. salivarius to hinder the biofilm will prevent S. mutans from becoming prevalent in the first place!

    • My understanding was that the primary reason why lactic acid is dangerous to teeth despite the buffering and continuous flushing provided by saliva is the fact that biofilms confine waste products like lactic acid to a tiny volume directly on top of the tooth surface. Without confinement, the lactic acid gets buffered and diluted by saliva very rapidly. I would be surprised if free-floating bacteria could alter oral pH to any significant degree. Do you have evidence/knowledge that they can, in fact, do this or were you speculating?

      • Hello, and welcome from the Internet! Congratulations on being the only visitor to comment on the microbiological basis of the story, which was the original intent of the piece–not to give people a sounding board to air their views on the evils of the Big Dental conspiracy.

        I suspect that the filtering ability (pore size) of the extracellular material in biofilms would be far larger than something like a 2 carbon acid degradation product, so the presence of the biofilm probably wouldn’t represent a significant free diffusion barrier to small molecules like this. This would be very easy to test, by forming a oral biofilm on a microscope slide, allow it to do it’s tooth decaying magic, and then going in with a pH sensitive fluorescent dye like aza-BODIPY. If there is a significant pH gradient in a biofilm due to acid production not being neutralized on the way in, the fluorescent signal by microscopy would give that away.

        There are many planktonic microorganisms that are present in large numbers in the oral cavity, despite not being biofilm associated. They can attach to surfaces and be retained in the many crevices in the mouth. The fascinating part of this (now 3 year old) story is the complex interactions between these organisms could conceivably be tweaked to inhibit biofilm formation in the first place. If one way to promote this is through a probiotic approach, well this is pretty easy, low cost thing to implement.

  2. Could it be that we cant all look into oral microbe and forget about tooth brushes because we all are not going to be resistant to dental caries. Because we all eat food with sugar which is another cause of caries. So we just all have to brush our teeth and take care of them like we should be doing.

    • You’re probably right; tooth decay is not a problem that is going to go away, due to our high sugar diet. Tooth decay is less of a problem today than it was 100 years ago though, because of a few innovations in oral care: 1) fluoridation of drinking water, and 2) prophylactic dental checkups and cleanings. I used to go to an old time dentist, who remarked that cavities in my kids’ generation were very rare in comparison to kids’ in my generation, even though I would argue that kids today have more processed sugars in their diets than I did.

      I think that we can use novel approaches like the one in this article to try an shift the balance even better in our favor. I’m still going to brush my teeth in a few minutes before going to work, and everyone in BIO230 can thank me later.

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