Physical and Biochemical Studies of Streptococcus mutans Sediments Suggest New Factors Linking the Cariogenicity of Plaque with its Extracellular Polysaccharide Content

Abstract

Cultures of Streptococcus mutans MFe28 (serotype h) were grown with differing extracellular polysaccharide (EPS) content. Biochemical and physicochemical characteristics considered relevant to caries were measured. Acid production parameters measured in a pH-stat were: Vm = 0.76 +/- 0.14 mumol/g/sec (wet weight); apparent Km (acid production) = 100 mumol/L; molar yield = 1.97 +/- 0.25 mol acid/mol glucose. Acid anion inhibition of acid production was also noted. Buffering by the pure washed bacterial residue required approx. 112 mumol of base/g (wet weight) of residue to change the pH from 4 to 6.5, and this dropped almost to zero as the EPS content increased to 100%. Diffusion coefficients (D) in the residues were independent of EPS content over a wide range. When the effusion method was used, De (glucose) and De (acetate) were (3.26 +/- 0.6) and (5.05 +/- 0.8) x 10(-6) cm2/sec, respectively. The extracellular fluid fraction, measured by inulin exclusion, increased from 0.33 for the pure bacteria to 0.78 for the pure EPS. It is shown how, by these factors alone, and without any need for diffusion restriction, plaque EPS may lead to a lower pH at the tooth surface, thus increasing the cariogenic challenge.

S. mutans biofilm model to evaluate antimicrobial substances and enamel demineralization

“…4,5 S. mutans are considered the most cariogenic microorganisms in dental biofilm due to their capacity to use dietary carbohydrates such as sucrose, to synthesize extracellular polysaccharides (EPS) and because of their acidogenic and aciduric properties. 4 EPS are important virulence factors of S. mutans because they promote bacterial adherence to the tooth surface, 6,7 contribute to the structural integrity of dental biofilms, 8,9 change the porosity of the biofilm 10 and consequently increase enamel demineralization. 11 Therefore, S. mutans biofilms have been used to evaluate their cariogenic properties due to difficulties of developing in vivo studies in controlled cariogenic situations.…”

Calcium binding to S. mutans grown in the presence or absence of sucrose

“…3 These EPS, mainly the insoluble ones (IEPS), play a significant role on the adhesion and accumulation of cariogenic streptococci on the tooth surface, especially S. mutans. 4 In addition, they change the biofilm structure, resulting in increased porosity, 5 which allows fermentable substrates to diffuse and be metabolized in the deepest parts of the biofilm. 6 Furthermore, since IEPS decrease the bacterial density of biofilms, 7,8 they may reduce the amount of biofilm calcium (Ca) binding sites 9 , which could also influence biofilm cariogenicity.…”

An in vitro microbial model associated with sucrose to produce dentin caries lesions

“…This sugar causes the biofilm microbiota to become more cariogenic [10] by producing higher levels of extracellular polysaccharides (EPS). EPS may enhance bacterial adherence to the tooth surface [11] and may also increase the biofilm porosity [12], producing local, low pH levels in the biofilm [13]. However, the majority of the existing microbial models use immersion in cultures inoculated with microorganisms, which only enables the demineralizing phase of the caries formation process.…”