GbpB Expression in Oral Isolates of Streptococcus mutans

Objective: Streptococcus mutans has been implicated as a primary causative agent of dental caries in humans and at least 4 glucan-binding proteins (Gbps) have been identified in the bacterium; GbpA, GbpB, GbpC, and GbpD. The contributions of GbpA and GbpC to S. mutans virulence have been investigated, while the function of GbpB is known to be different from that of the other Gbps. The purpose of this study was to analyze the relationship between GbpB expression and cariogenic properties using clinical isolates. Methods: Oral isolates of S. mutans were randomly selected from our laboratory stock and cultured, then whole cells and culture supernatants that were concentrated with ammonium sulfate of clinical isolates were prepared. Western blotting analysis of three of the samples were carried out with anti-sera specific for GbpB, and the results compared with those of the strains MT8148 and UA159. Next, chain length, doubling time, and sucrose-dependent adherence were tested in all strains and compared with those of GbpB-deficient mutant strains constructed by insertional inactivation of the gbpB gene. Results: Western-blotting assays of GbpB showed that the strains had three different expression patterns, i.e., no, one, or two bands. The chain length and doubling time of the test strains with no bands were similar to those of the GbpB-deficient mutant strains. Also, the rates of sucrose-dependent adherence for the strains with two bands were significantly lower than for the other strains. Conclusion: Our results indicate that the diverse expression of GbpB has an influence on dental caries development in individual patients.