Cariogenicity of Mucoid-Form Streptococcus mutans and Its Revertants

The virulence of a large mucoid-form colony of Streptococcus mutans strain ZO-1 serotype c on Mitis Salivarius agar and its revertants were investigated. In rat caries experiments, the caries score of ZO-1 was very high, similar to that of the Streptococcus mutans reference strain. Their revertants appeared in the ZO-1 strain infected group in an in vivo experiment. The frequency range of the revertants varied from 0.1-62.5% (average : 21.9%). The ability to form plaque from sucrose was similar in ZO-1 and revertant strains compared with the S. mutans reference strain. Acid production in all test strains was similar. The production of polysaccharides from sucrose of the ZO-1 strain mainly involved water-soluble fructan, however, revertants did not produce as much fructan as the ZO-1 strain. The soluble and insoluble glucan synthesis of ZO-1 and the revertants were similar to those of the S. mutans reference strain. In in vivo experiments, the caries scores of revertant strain infected group was similar to that of reference strain of S. mutans infected group. The mucoid-form colony did not appear from the revertant infected group. The mucoid-form ZO-1 and its revertant strains exhibited a cariogenic potenial similar to the S. mutans reference strain.