SUCROSE-DERIVED EXOPOLYMERS HAVE SITE-DEPENDENT ROLES IN STREPTOCOCCUS MUTANS-PROMOTED DENTAL DECAY

We have constructed a panel of mutants of S. mutans V403 which are def ective in one or more of the glucosyltransferase genes (gtfB,C or D) o r the fructosyltransferase gene (ftf). These strains have been tested for virulence in a gnotobiotic rat caries model with reference to both buccal (smooth surface) and sulcal (pit and fissure) carious lesions. Our data suggest differing roles for degradable and non-degradable po lymers at buccal and sulcal sites. Non-degradable polymers (made by pr oducts of the gtfB and C genes) contributed significantly to the sever ity of smooth surface lesions. However, our studies suggested their ro le in pit and fissure lesions was not as important as the role of degr adable polymers. Specifically, a mutant deficient in the major insolub le glucan synthesizing activity (product of the gtfB gene) was 25% mor e cariogenic on sulcal surfaces than was the wild-type V403 strain. We propose that extracellular glucosyltransferases and fructosyltransfer ase compete for sucrose and that this competition influences pathogeni city at differing tooth sites.