Effects of Antibodies against S. sobrinus components on its Colonization

Objectives: The cell surface protein antigen (PAg) and glucosyltransferases (GTFs) produced by Streptococcus sobrinus are major colonization factors of the organism, and the inhibition of these two factors should provide protection against dental caries. In this study, we constructed a fusion protein (PAgA-GB) composed of the alanine-rich region (PAgA) of PAg and the glucan-binding domain (GB) of GTF-I enzyme catalyzing the synthesis of water-insoluble glucan from sucrose. Materials and methods: The recombinant PAg, GTF-I, and PAgA-GB were purified from cell extracts of Escherichia coli harboring each gene, and rabbit antibodies against these recombinant proteins were prepared. The effects of these antibodies on the sucrose-independent and -dependent adhesion of S. sobrinus MT8145 to saliva-coated hydroxyapatite beads (S-HA) were examined. The differences in the inhibition of the adhesion of S. sobrinus to S-HA were compared, between pre-immune antibodies and antibodies against each protein antigen, using Bonferroni multiple comparisons. Results: Antibodies against PAg significantly inhibited the adhesion of S. sobrinus in the absence of sucrose, but not in the presence of sucrose, while antibodies against GTF-I significantly inhibited only the sucrose-dependent adhesion. Significant inhibition of both sucrose-dependent and -independent adhesion of S. sobrinus to S-HA was observed in the presence of anti-PAgA-GB antibodies. Conclusions: Antibodies against the PAgA-GB fusion protein suppressed colonization of S. sobrinus in vitro. Therefore, immunization with PAgA-GB might be useful for controlling the colonization of teeth by S. sobrinus.