Surprising News About Caries

Microorganisms often join together in biofilms of bacteria and fungi to be more survivable. Bacterial biofilms are dangerous for humans because the immune system can hardly reach and fight the pathogens living in them. One example is caries. Sugar serves as food for the bacteria and fungi living in the mouth. They deposit themselves on the teeth as an acid-producing biofilm and destroy the tooth enamel.

Hyun Koo, University of Pennsylvania, Philadelphia, PA, USA, and colleagues have studied saliva samples from young children suffering from aggressive tooth decay and found that biofilms of Streptococcus mutans bacteria and the yeast Candida albicans exist on teeth. The associations of bacteria and fungi showed surprising mobility. The researchers compared them to a superorganism with new capabilities.

From experiments in which the researchers propagated bacteria, fungi, and tooth-like material in human saliva and then observed it with real-time live microscopy, they found that the biocoenosis on the tooth surfaces consists of bacterial clusters anchored in a network of fungal yeasts and filamentous protrusions called hyphae. Bacteria and fungi are embedded in an adhesive-like material, an extracellular polymer. On the tooth surface, these structures are difficult to remove or kill.

Neither the fungi nor the bacteria can move. Together, they use the fungal hyphae to move continuously and rapidly. This has not been observed in other types of microbes, so far. Using the fungal hyphae, the bacteria-fungi formations anchor themselves to the teeth, transporting their germs across the tooth surfaces. These continuous movements are faster than average, with speeds of more than 40 µm/h. In addition, significant jumps of more than 100 µm were observed.

Both components of the microbial compound are initially present in saliva before they colonize the tooth surface together. Therefore, the researchers suspect that an effective therapy should already start there. Such dynamic, coordinated behavior between individual organisms may also occur in other biofilm-forming communities that cause human diseases and biofouling in the environment.