Genetically engineered organisms that attack decay-causing bacteria could represent a significant component in the war against tooth decay, according to a report in the Washington Post.

The report details several approaches to eliminating or rendering harmless the Streptococcus mutans bacteria that are responsible for converting sugars in food into lactic acid, the chemical that dissolves tooth enamel and causes decay.

Researchers from the Karolinska Institute's Center for Oral Biology in Sweden have modified the Lactobacillus zeae bacterium to carry an antibody against S. mutans that can attach to the surface of S. mutans and render it harmless, the report says. Initial results showed a 40 percent reduction in early cavities for subjects given the bacterium.

At the University of Florida College of Dentistry, scientists have created a strain of S. mutans that lacks the gene necessary to produce the decay-causing lactic acid. The strain is activated by a synthetic nutrient not normally found in the human diet to provide some assurance against unintended consequences of introducing the modified bacteria into the oral environment.

National Institute of Dental and Craniofacial Research director Dr. Lawrence Tabak is quoted in the Post story expressing concern that bacteria engineered to kill S. mutans might leave open a niche into which worse bacteria might move. Instead, he prefers the concept of replacing harmful S. mutans with a species engineered to rebuild tooth surfaces.

"Some microorganisms produce acids, but others produce bases, and these bases provide a milieu that favors remineralization," he said. "The processes of tooth decay and remineralization are very dynamic processes, and we now have a whole host of tools to look at this in real time."

Another scientist from the University of Florida is taking just such an approach, the report says, with a strain of S. mutans engineered to increase production of the enzyme urease, which converts urea into ammonia to create conditions conducive to enamel production. Initial tests show fewer cavities in laboratory animals whose mouths were colonized with the modified bacteria, according to the report.