Serotype-dependent inhibition of glucan synthesis and cell adherence of Streptococcus mutans by antibody against glucosyltransferase of serotype e S. mutans

Sulfated vizantin inhibits biofilm maturation by Streptococcus mutans

Streptococcus mutans is the main pathogen of dental caries and adheres to the tooth surface via soluble and insoluble glucans produced by the bacterial glucosyltransferase enzyme. Thus, the S. mutans glucosyltransferase is an important virulence factor for this cariogenic bacterium. Sulfated vizantin effectively inhibits biofilm formation by S. mutans without affecting its growth. In this study, less S. mutans biofilm formation occurred on hydroxyapatite discs coated with sulfated vizantin than on noncoated discs. Sulfated vizantin showed no cytotoxicity against the human gingival cell line Ca9-22. Sulfated vizantin dose-dependently inhibited the extracellular release of cell-free glucosyltransferase from S. mutans and enhanced the accumulation of cell-associated glucosyltransferase, compared with that observed with untreated bacteria. Sulfated vizantin disrupted the localization balance between cell-associated glucosyltransferase and cell-free glucosyltransferase, resulting in inhibited biofilm maturation. These results indicate that sulfated vizantin can potentially serve as a novel agent for preventing dental caries.

Oral passive immunization against dental caries in rats by use of hen egg yolk antibodies specific for cell-associated glucosyltransferase of Streptococcus mutans

The effect of polyclonal egg yolk immunoglobulin G antibodies (yIgG) raised against whole cells, cell-free (CF) glucosyltransferase (GTase), or cell-associated (CA) GTase of serotype c Streptococcus mutans was examined in terms of in vitro inhibition of virulence-related factors of S. mutans and protection of S. mutans-infected rats against the development of dental caries. Hens (18 weeks old) were immunized with formalin-treated whole cells, purified CF-GTase, or CA-GTase together with Freund's complete adjuvant. In addition, yIgG to surface protein antigen was used in some in vitro experiments for comparison with other antibodies. yIgG was purified by ammonium sulfate precipitation followed by DEAE-Sephacel column chromatography or fractional precipitation with ethanol. Purified yIgG was found to be a 220-kDa protein, which was dissociated into heavy and light chains upon addition of 2-mercaptoethanol. yIgG to whole cells and surface protein antigen gave a heavy aggregation of S. mutans organisms, while yIgG to CF- and CA-GTase specifically inhibited the enzymatic activity of the respective GTase. yIgG to CA-GTase and whole cells was found to clearly suppress the adherence of S. mutans cells to a glass surface. Specific-pathogen-free Sprague-Dawley rats that had been infected heavily and repeatedly with S. mutans and fed diet no. 2000 developed severe dental caries, while rats fed diet 2000 containing greater than or equal to 0.1% yIgG to CA-GTase showed a statistically significant reduction in dental plaque accumulation and caries development. Administration of yIgG to CF-GTase and whole cells failed to protect against caries. These results clearly suggest that yIgG to S. mutants CA-GTase specifically inhibited a virulence factor of this organism, i.e., insoluble glucan-synthesizing CA-GTase, resulting in a significant reduction in the development of dental caries.

Electrophoretic studies of extracellular glucosyltransferases and fructosyltransferases from seventeen strains of Streptococcus mutans

Streptococcus mutans was classified by the electrophoretic properties of glucosyltransferases (GTases) and fructosyltransferases (FTases). The cells of serotypes a, d and g did not release extracellular FTases, although those from other serotypes did. The enzymes from cells of serotypes d and g synthesized a good deal of insoluble polysaccharide compared with other serotypes. The enzymes were applied to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and polyacrylamide gel-isoelectric focussing (PAG-IEF). Gels were stained for their activity and protein content. Enzymes belonging to the same serotype gave the same specific pattern on both gels. The seven serotypes could be classified into the following four groups: serotypes d and g, serotype a, serotypes c, e and f, and serotype b. The results agree well with some previous reports based on other methods. The molecular weights of three GTase bands were 156K, 146K and 135K, and of four kinds of FTase bands were 108K, 95K, 80K and 76K. The isoelectric points of main enzymes were 4.25, 4.60, 5.00, 5.55 and 5.70. Those of FTases were 4.25 and 4.60.

Effects of oxygen on glucose-limited growth of Streptococcus mutans

Aerotolerance in the growth of Streptococcus mutans and related streptococci was examined under glucose-limited conditions. The growth rate of all strains tested was more or less retarded when they were transferred from anaerobic to aerobic conditions. As for growth yield, however, some strains (group 1) showed reduced values for the increment of cellular dry weight change (in grams per mole of glucose), whereas others showed either unaltered (group 2) or increased (group 3) yields. The characteristic feature of strains in groups 2 and 3 was their high activity of both glucose- and pyruvate-dependent oxygen uptake when strains were grown under aerobic conditions. By contrast, the activity of pyruvate-dependent oxygen uptake by group 1 strains was negligibly low, whether grown under aerobic or anaerobic conditions. Some strains (group 1a) consumed oxygen in the presence of glucose at a much faster rate than others did (group 1b). There seems to be a good correspondence of these aerotolerance groupings to those based on serotypes of S. mutans. Thus, the groups 1a, 1b, 2, and 3 correspond to serotypes g, a+d, c+f, and b, respectively.

Inter-serotype comparison of polysaccharides produced by extracellular enzymes from Streptococcus mutans

The biochemical and morphological characteristics of polysaccharides synthesized from sucrose by extracellular enzymes from D-glucose-grown Streptococcus mutans representing serotypes a-g were compared. The polysaccharides synthesized by the enzymes from serotypes a, d, and g formed visible aggregates and firmly adhered to glass surfaces, whereas those formed by the enzymes from serotypes b, c, e, and f floated homogeneously and were poorly adherent. The enzymes of serotypes a, d, and g produced large amounts of water-insoluble polysaccharides (IPs, D-glucans), and those of serotypes b, c, e, and f water-soluble polysaccharides (SPs, D-glucans and D- fructans ). As compared with the IPs of serotypes b, c, e, and f, the IPs of serotypes a, d, and g (a) contained a higher proportion of (1----3)-alpha-D-glucosidic linkages and alpha-D-(1----3,6) branch linkages; (b) showed higher susceptibility to (1----3)-alpha-D-glucanase (serotype a excepted) and lower (1----6)-alpha-D-glucanase sensitivity; (c) contained larger amounts of high-molecular-weight fractions; (d) showed higher intrinsic viscosities (serotype b excepted); and (e) had lower S. mutans cell-agglutination activities. On electron-microscope observation, the IPs of all serotypes showed two fibrillar components; a double-stranded fibril, with short, fluffy protrusions extending out of its periphery, and a fine, single-stranded fibril. Thus, the serotypes could be divided into two major groups: a, d, and g; and b, c, e, and f. No similar grouping of serotypes was indicated by the chemical and morphological properties of SPs.

Virulence factors of Streptococcus mutans and dental caries prevention

Streptococcus mutans possesses the abilities to adhere to pellicle-coated tooth surfaces and to form acids - two characteristics associated with the cariogenicity of this micro-organism. De novo synthesis of insoluble glucan by S. mutans glucosyltransferase from sucrose is essential in the adherence process. Therefore, agents which interfere with the adherence ability of S. mutans would be useful for controlling dental caries. In the present report, we have summarized our recent findings concerning virulence factors of S. mutans and means for prevention of S. mutans-induced dental caries.

Production of monoclonal antibody against a glucosyltransferase of Streptococcus mutans 6715

A mouse hybrid cell line secreted monoclonal antibody which reacted specifically with Streptococcus mutans 6715 (serotype g) glucosyltransferase (GTase)-synthesizing water-insoluble glucan and inhibited with enzyme reaction. The antibody was cross-reactive with GTase of serotype d but not with GTase of other serotypes of S. mutans when an enzyme-linked immunosorbent assay was used.

Immunochemical properties of glucosyltransferases from Streptococcus mutans

Antiserum against purified mutansynthetase (EC 2.4.1.?) of Streptococcus mutans 6715 (serotype g), which is responsible for the synthesis of water-insoluble glucan (ISG) in the presence of both sucrose and water-soluble glucan, was prepared. The specificity of the antiserum was tested by using crude enzyme preparations (CEPs) of S. mutans strains of various serotypes. On immunodiffusion, the antiserum cross-reacted with CEPs from strains of serotypes a (HS-6 and AHT), d (OMZ176), and g (OMZ65 and KIR), but not with those from strains of serotypes b (BHT and FA-1) and c (GS-5 and Ingbritt). The antiserum inhibited the synthesis of ISG by crude or purified mutansynthetase of S. mutans 6715. The activities of ISG synthesis by CEPs from the strains antigenically related in the foregoing immunodiffusion were inhibited by the antiserum against strain 6715 mutansynthetase. The antiserum, however, also inhibited the enzyme activity of the strains of serotype b. The finding that the antiserum against purified dextransucrase of S. mutans HS-6 inhibited ISG synthesis by a CEP of strain HS-6 and also by CEPs of antigenically related strains suggested that dextransucrase activity is involved in ISG synthesis.

Susceptibility of rats, hamsters, and mice to carious infection by Streptococcus mutans serotype c and d organisms

Susceptibility of rats, hamsters, and mice to carious infection by S. mutans serotypes c and d was compared. S. mutans serotype c induced a similar level of carious lesions at experimental periods of 68, 82, and 98 d in rats, hamsters, and mice, respectively. On the other hand, S. mutans serotype d developed a high level of caries at those experimental periods in rats and hamsters, whereas in mice it showed weak caries activity.

Interference of secretory immunoglobulin A with sorption of oral bacteria to hydroxyapatite

The potential of secretory immunoglobulin A (S-IgA) to interfere with the initial phase of dental plaque formation was studied by using an in vitro method which permits the quantitative determination of the sorption of radiolabeled oral bacterial cells to hydroxyapatite (HA) beads. The importance of specific S-IgA antibodies was evaluated by a comparison of the effect of pure preparations of colostral S-IgA, polymeric myeloma IgA, or preabsorbed S-IgA. Specific antibody molecules bound at the HA surface significantly enhanced the sorption of two Streptococcus sanguis strains. In contrast, HA-bound S-IgA antibodies inhibited the sorption of Streptococcus mitior and Streptococcus salivarius. The same was true for Streptococcus mutans cells, but only when they were propagated in the absence of sucrose. Suspended in saliva, cells of all streptococcal species adhered in significantly lower numbers to HA. Comparative experiments with bacteria suspended in solutions of various preparations of IgA or immunoglobulin-deficient salivas with S-IgA or myeloma IgA added indicated that the adherence inhibition seen with S. Sanguis, S. mitior, S. salivarius, and glucose-grown S. mutans was partly attributable to functions of S-IgA antibodies. Under the in vitro conditions of the study, S-IgA antibodies had no effect on the sorption of sucrose-grown S. mutans, Actinomyces viscosus, and Actinomyces naeslundii to HA. The results indicated that S-IgA can interfere with the sorption of some oral bacteria to HA by several different functions.

Biology, immunology, and cariogenicity of Streptococcus mutans

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Isolation and serotyping of Streptococcus mutans from teeth and feces of children

Streptococcus mutans were detected in the feces from 10 of 29 caries-active patients, aged 4 to 9 years. The percentage of S. mutans to the total counts of facultatively anaerobic streptococci on mitis salivarius agar (Difco Laboratories) varied from 0 to 72.5%. S. mutans were then isolated from dental plaque of sound teeth and carious dentin of the 10 subjects known to harbor S. mutans in the feces. The frequency distribution of various serotypes of these dental and fecal isolates of S. mutans was compared by the immunodiffusion technique. Of the total 1,047 isolates (290 isolates from feces, 289 from dental plaque, and 468 from carious dentin), type c isolates were most prevalent (ca. 66%). Serotype d, e, f, and g isolates were also found but in far lower frequencies. Plural serotypes of S. mutans were occasionally found in dental and fecal samples of a single subject. For two subjects, relatively rare serotypes of S. mutans in the population examined, serotype e, f, or g, were predominantly found in their fecal and dental samples and those of their siblings and mother, suggesting an intrafamilial transmission of S. mutans.