A surface protein antigen (PAc) of Streptococcus mutans, particularly the A-region of the molecule, has been reported to interact with salivary components on the tooth surface. It might be a candidate antigen inducing the production of antibodies against the adherence of S. mutans to the tooth surface. We investigated the effects of monoclonal antibodies (MoAbs) obtained by immunization of synthetic PAc peptides that completely correspond to the amino acid sequence of part of the A-region. These MoAbs recognize several core B-cell epitopes in the sequence. Two (KH5 and SH2) of these antibodies reacted with both S. mutans and Streptococcus sobrinus, but not with Streptococcus sanguis, Streptococcus salivarius, Porphyromonas gingivalis or Lactobacillus casei. They clearly inhibited the real-time adherence of S. mutans to salivary components in a biosensor. KH5, which showed a real-time inhibition (71%), also significantly prevented the recolonization of S. mutans on the tooth surface in rats. These results suggested that the core B-cell epitope (-Y---L--Y----) recognized by KH5 was the essential sequence in the antigenic epitopes of PAc protein recognized specifically by the inhibitory antibody. Therefore, the amino acid residues were found to be important in the initial attachment of S. mutans to the tooth surface. These results provide for the mechanism of PAc molecule in the initial attachment of S. mutans on the tooth surface and more effective designs for the removal of S. mutans and S. sobrinus from the oral cavity.

Oral streptococci are present in large numbers in dental plaque and account for approximately 20% of the total number of salivary bacteria (25). Furthermore, several types of these bacteria interact with the enamel salivary pellicle to form a biofilm on tooth surfaces. Early biofilm formation occurs by attachment and colonization of a variety of streptococci and is dependent on both the species involved and the surface composition (2,12,26,33). The subsequent accumulation and growth of attached bacteria result in microcolonies that increase in size and eventually form a towering pillar-or mushroom-shaped biofilm (4). There is a strong relationship between the attachment, detachment, and aggregation of these organisms in plaque on tooth surfaces and the presence of dental decay in humans (14,24).Members of the mitis group of streptococci, which includes Streptococcus gordonii, Streptococcus mitis, Streptococcus oralis, Streptococcus parasanguis, and Streptococcus sanguis (16), are prominent components of the human oral microbiota and play a significant role as pioneer colonizers in the development of dental plaque (9, 34). Mutans streptococci (Streptococcus mutans and Streptococcus sobrinus) are also known to be primarily involved when the bacterial flora forms on the tooth surface. S. sanguis has been shown to have a strong association with saliva components; however, it was easily dissociated, compared with other streptococci, by using a BIAcore system, and although this organism showed a higher binding resonance unit (RU) value than S. mutans for association, it could be easily dissociated from saliva components (17).S. mutans, S. sobrinus, and S. gordonii produce surface protein antigens (PAc, AgI/II, B, P1, SpaP, and MSL-1), PAg (SpaA), and SspB (SspA), which have molecular masses of approximately 190 kDa (6,10,18,32,36,38), 170 kDa (22,44), and 180 kDa (5, 15), respectively, and interact with salivary components, including lysozyme (37, 40), amylase (37), 18,000-and 38,000-Da prolinerich proteins (32), and agglutinin (5). of in the alanine-rich repeating region (residues 219 to 464, A region) of the PAc molecule is an important region for the adherence of S. mutans to the tooth surface (39,43). Furthermore, the T-and B-cell epitopes overlap (39,41), and the epitope XYXXXLXXYXXXX, an essential sequence in the antigenic epitopes of the PAc protein, is recognized specifically by the inhibiting antibody (42). In the N-terminal region (residues 1 to 429) sequenced from S. gordonii M5 (previously designated S. sanguis), the cell surface adhesins SspB and SspA showed extensive homology [63 and 60% identity, respectively, with SpaP (PAc)] (6). The A region is composed of three long and two incomplete repeating sequences (26). Therefore, each repeating sequence contains sequences that are homologous to the amino acid sequence 365 TYEAALKQYEADL 377 of PAc(365-377), which is an important region for the initial attachment of S. mutans to the tooth surface (31, 36). The differences between the alanine-rich sequence in ...

Oral streptococci are present in large numbers in dental plaque and several types interact with the enamel salivary pellicle to form a biofilm on tooth surfaces. The respective affinity of individual streptococci for salivary components has an influence on the etiologic properties of oral biofilm in the development of dental caries. We studied real-time biospecific interactions between oral streptococci and salivary components utilizing biosensor technology to analyze surface plasmon resonance. Streptococcus sanguis and Streptococcus mutans showed significant responses for binding to salivary components, in comparison with other bacteria. Further, the association rates (4.1 x 10-11/bacterium) and dissociation rate (5.7 +/- 0.9 x 10-3 Second(s)-1) were higher for S. sanguis than for S. mutans (2.4 x 10-11 and 2.9 +/- 0.8 x 10-3) and Streptococcus mitis (1.3 x 10-11 and 3.5 +/- 1.3 x 10-3). However, the association equilibrium constants (8.2 S/bacterium) for S. mutans was 2 times higher in than S. mitis (3.8) and slightly higher than S. sanguis (7.2). These findings may provide useful information regarding the mechanism of early biofilm formation by streptococci on the tooth surface.