03 November 2017

Life in Stone

Scientists have found out why carious bacteria do not kill themselves

RIA News

Biologists from Switzerland have uncovered a curious mechanism that helps carious bacteria not to kill themselves inside the tartar and does not allow the body to restore the destroyed enamel, according to an article published in the journal PLoS One (Exopolysaccharides regulate calcium flow in cariogenic biofilms).

"The polysaccharide molecules that bacteria secrete during the decomposition of dental tissues absorb calcium ions that are toxic to microbes and interfere with the remineralization of enamel, which needs this element to restore. This clarifies a lot about the role calcium plays in the appearance of caries," said the first author of the article Monika Astasov–Frauenhoffer from the University of Basel (in a press release How Caries-Causing Bacteria Can Survive in Dental Plaque – VM).

As biologists explain, caries appears on the surface of our teeth due to the multiplication of several strains of Streptococcus mutans and other bacteria that secrete large amounts of acid into saliva and on the surface of teeth.

An increase in the acidity of saliva leads to the fact that the "cement" that glues the enamel grains together gradually corrodes, and new colonies of bacteria settle in the resulting microcracks, whose appearance accelerates the process of tooth destruction and leads to the formation of a carious cavity.

The main problem of this theory of caries development, as Astashov-Frauenhoffer explains, is that the destruction of tooth enamel and the formation of tartar should lead to the mass death of the microbes themselves due to the fact that a huge amount of calcium ions toxic to streptococci and other carious microbes will accumulate in their nutrient medium.

However, this does not happen, which poses another mystery to scientists – why caries does not "self-destruct" and how these microbes suppress the process of restoring the enamel they destroy. Trying to solve this mystery, Astashov-Frauenhoffer and her colleagues observed how carious bacteria and other microbes reacted to an increase in the concentration of calcium in their nutrient medium.

These experiments revealed an unusual thing – the resistance of carious bacteria to "poisoning" with calcium depended not on differences in their DNA, but on how many long chains of sugars were contained in their colonies. These polysaccharides, as scientists explain, were considered one of the components of the "glue" with which microbes glue themselves to the surface of teeth and form plaque.

It turned out that this "glue" has another function – it absorbs "extra" calcium ions, which protects microbes from death, and at the same time deprives the body of resources to restore enamel. This allows microbes to survive inside the tartar and destroy the tooth for an almost unlimited amount of time.

The main condition for the formation of this "glue", as scientists note, is the presence of molecules of at least one type of sugars in human saliva. This may explain why sugar accelerates the development of caries and why avoiding its use reduces the likelihood of tooth decay by microbes.

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