Early Childhood Tooth Decay Linked to Unusual Collaboration of Bacteria and Fungi

Preschool children are susceptible to a from of tooth decay known as early childhood caries, and researchers have linked the occurrence of the painful and aggressive form of decay to a nefarious partnership between a bacterium and a fungus.

Early childhood caries, or ECC - also known as baby bottle tooth decay or bottle rot - can lead to tooth decay so severe that it requires a visit to the operating room for treatment.

According to the American Academy of Pediatric Dentistry, the consumption of liquids containing fermentable carbohydrates such as milk, juice and formula increases the risk of ECC.

For years, oral health professionals have linked ECC and other dental caries to the bacterium Streptococcus mutans. But according University of Pennsylvania School of Dental Medicine researcher Hyun Koo and his collaborators, the bacterium is not the sole microbial culprit in this form of childhood tooth decay.

In the most of the cases of ECC the researchers encountered, the bacterium was always present along with a fungus known as Candida albicans. The bacterium sticks to teeth by converting sugars into a sticky goo called extracellular polysaccharide (EPS.) The Candida fungus adheres mainly to the tongue and cheeks, but had rarely been seen in dental plaque.

"However, we and others noticed that Candida was very frequently observed in plaque from patients who have early childhood caries," Koo said. "We were puzzled! Candida usually does not associate with S. mutans, nor does it colonize teeth very effectively."

To explore this further, the researchers set up an experiment with laboratory rats. They found that in rats, Streptococcus mutans coupled with the fungus Candida albicans doubled the number of cavities and increased their severity as well.

The researchers discovered that the compound that that causes Streptococcus mutans to react with sugar and form EPS also enables the Candida fungus to produce a glue-like polymer in the presence of sugar, allowing it to do something it ordinarily cannot: adhere to teeth and bind to S. mutans.

When this happens, the fungus contributes to the bulk of plaque build-up on teeth.

"The combination of the two organisms led to a greatly enhanced production of the glue-like polymer, drastically boosting the ability of the bacterium and the fungus to colonize the teeth, increasing the bulk of the biofilms and the density of the infection," Koo said. "All that led to greatly elevated accumulation next to the teeth of the acid that dissolves enamel, leading to cavity formation."

"This represents a truly unique physical interaction where a bacterially-produced product attaches to and functions on the surface of an organism from another kingdom, converting this normally innocuous (with respect to teeth) fungus into a fierce stimulator of cariogenic biofilm formation," Koo added.

Koo and his collaborators will publish their research in the May edition of the journal Infection and Immunity.