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Fighting Cavities
Bacterium that causes tooth decay, S. mutans, is sequenced
  

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Scientists have sequenced the genome of a microbe that lives in the mouth and causes most of the cavities in the world. The bacterium, Streptococcus mutans, sticks to the surface of teeth and subsists on a diverse group of carbohydrates. While metabolizing sugar and other energy sources, the microbe produces acid that causes cavities in teeth.


Map of the S. mutans genome. View map

The researchers have identified several hundred genes that appear to be unique to the organism. These are potential drug targets because disrupting them would disable the pathogen without harming other bacteria in the mouth.

"We don't want to kill useful bacteria," says Joseph J. Ferretti, of the University of Oklahoma Health Sciences Center in Oklahoma City, who led the study. His laboratory is trying to identify proteins that, when blocked, inhibit an essential biological process—such as the pathogen's adherence to teeth.

"In the presence of highly refined sugars, the bacterium makes a sticky substance that allows it to adhere to smooth surfaces like glass or teeth," says Ferretti. There, while producing energy, the microbe also produces the acid that causes the demineralization of teeth.

More than 200 species of bacteria are associated with dental plaque, but only S. mutans has been linked consistently to tooth decay. Though not fatal, tooth decay is one of the most common infectious diseases in humans. Cavities are the reason for half of all dental visits in the U.S., according to Ferretti.

The bacterium has about 1,900 genes. The sequencing, done in collaboration with Bruce A. Roe at the University of Oklahoma in Norman, revealed extensive sets of genes for metabolizing and transporting carbohydrates. The findings are reported in Proceedings of the National Academy of Sciences.

Researchers in the field have discussed the idea of a vaccine for at least two decades, and the new data may speed the identification of useful targets. "The genome sequence provides us with new tools and opens interesting avenues of research," says Ferretti.

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Ajdic, D. et al. Genome sequence of Streptococcus mutans UA159, a cariogenic dental pathogen. Proc Natl Acad Sci USA. Published online October 23, 2002.
 

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