Treatment blocks sites for dental bacteria

Armed with toothbrushes, toothpastes, and floss, people wage a daily war against cavity-causing bacteria. Now, researchers in England have found another way to defeat those microscopic foes. Teeth treated with a new synthetic molecule remain free of the feared bacteria for up to 4 months, they report.

 Most cavities are caused by the bacterium Streptococcus mutans, which binds to receptor proteins on the surface of teeth and collects into the film of plaque that dentists warn their patients about. Unlike other bacteria in the mouth, S. mutans produces lactic acid, which erodes tooth enamel.

"If you can prevent infection with Streptococcus mutans, you will actually prevent tooth decay," says Charles G. Kelly of the Guy's, King's, and St. Thomas' Hospitals Medical and Dental School in London.

 Kelly and his colleagues pursued this goal by creating a peptide, or short sequence of amino acids, that blocks the receptors and thus prevents S. mutans from sticking to teeth. Earlier work had shown that S. mutans possesses a large protein, called adhesin, that binds to receptors. Kelly's team identified and synthesized a critical 20-amino acid portion of adhesin that, in the test tube, successfully binds to the receptors. The researchers then tested how well the synthetic peptide prevents S. mutans from colonizing human teeth.

 The researchers first treated three groups of four volunteers with an antiseptic mouthwash for 9 days to remove all microbes from their mouths. Over the following 3 weeks, a solution containing the peptide was dripped twice a week onto the teeth of one group, which also used a daily mouthwash with the peptide. The other two groups received similar treatments with a different peptide or no peptide at all. The researchers then monitored growth of S. mutans on the volunteers' teeth.

 Those who received the binding peptide remained free of S. mutans for at least 3 months. The bacteria appeared on the teeth of the others within 3 weeks, however. Kelly and his colleagues report their findings in the January Nature Biotechnology.

 After treatment, the peptide remains in the mouth for only about 6 hours, Kelly says, but it appears to exert long-term antimicrobial effects. "If you can hinder [ S. mutans] colonization initially, other bacteria occupy the niche," Kelly says. Plaque formed by harmless bacteria acts as a protective film, crowding out the acid-producing S. mutans.

 The results of the study are "quite striking," says Randall T. Irvin of the University of Alberta in Edmonton. "If this is indicative of what will happen in a larger group, it's encouraging." He expects that bacteria subjected to this treatment would evolve resistance less readily than when attacked with antibiotics.

 This approach could be applied to other microbial targets, Irvin says, "but it will take a lot of work." Receptor binding often triggers normal cell processes, so the peptides would have to be designed to deflect bacteria without interfering with those effects.