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

Abstract

The aim of this study was to validate a model of S. mutans biofilm formation, which simulated 'feast-famine' episodes of exposure to sucrose that occur in the oral cavity, showed dose-response susceptibility to antimicrobials and allowed the evaluation of substances with anticaries potential. S. mutans UA159 biofilms were grown for 5 days on bovine enamel slabs at 37°C, 10% CO 2 . To validate the model, the biofilms were treated 2x/day with chlorhexidine digluconate (CHX) at 0.012, 0.024 and 0.12% (concentration with recognized anti-plaque effect) and 0.05% NaF (concentration with recognized anti-caries effect). CHX showed dose-response effect decreasing biomass, bacterial viability and enamel demineralization (p < 0.05). Whereas, 0.05% NaF did not show antimicrobial effect but had similar effect to that of 0.12% CHX decreasing enamel demineralization (p < 0.05). The model developed has potential to evaluate the effect of substances on biofilm growth and on enamel demineralization.

The effect of iron on Streptococcus mutans biofilm and on enamel demineralization

“…mutans biofilms were formed on bovine dental blocks suspended vertically in culture medium 14 using a validated model, which was previously shown to have a dose-dependent response for evaluating the effect of antimicrobial substances on biofilm formation and on enamel demineralization. 15 The biofilms were exposed eight times/day for 2.5 min in a 10% sucrose solution; after the biofilms were allowed to grow for 48 h, they were treated two times/ day for 1 min according to the treatment groups described above. The pH of the culture medium was determined every 24 h as an indicator of the biofilm's acidogenicity.…”

“…One hundred and fifty blocks of enamel (4 × 7 × 1 mm) were prepared from dental crowns of bovine incisors as described, 15 and 54 blocks with a hardness of between 313.8 and 331.7 kg/mm 2 were selected; these were then randomly divided into six groups of nine blocks each to receive the treatments described above.…”

“…The blocks were sterilized in an autoclave 15 and pre-treated with clarified human saliva for the formation of salivary acquired pellicles. 14 …”

“…The plates were incubated in 10% CO 2 for 8 h at 37°C. 15 After 8 h, the biofilms were transferred to plates containing 2.0 mL of UTYEB and 0.1 mM glucose (the basal concentration of glucose in saliva) and incubated for another 16 h. On the following day, 24 h after the start of the experiment, the biofilms were transferred to fresh media and then treated with 10% sucrose for 2.5 min eight times/day at predetermined times (8:00, 9:30, 11:00, 12:30, 14:00, 15:30, 17:00, and 18:30). These first two days were used for bacterial adhesion and to allow the initial formation of the biofilm as described previously.…”

“…These first two days were used for bacterial adhesion and to allow the initial formation of the biofilm as described previously. 15 After the biofilm had grown for 48 h, the treatments (G1-G6) began, with the eight exposures to sucrose maintained. The culture medium was changed every 24 h on the morning of each day.…”