Extended biofilm formation time by Streptococcus sanguinis modifies its non-cariogenic behavior, in vitroAbstract
Although the commensal Streptococcus sanguinis [ S. sanguinis] is isolated from caries-free people, it can ferment carbohydrates producing acids. We aimed to characterize S. sanguinis cariogenic potential as a function of different enamel biofilm formation periods, in vitro. Saliva-coated enamel slabs were inoculated with S. sanguinis to form initial biofilms for 8, 12 or 16 h in presence of sucrose and followed by a period in medium with glucose for 16, 12 or 8 h, respectively, until completion of 24 h. To simulate cariogenic challenges, S. sanguinis biofilms were exposed to 10% sucrose for 5 minutes, 3x/day for 5 days. Biofilm biomass, viable cells, total proteins, intracellular and extracellular polysaccharides production, acidogenicity and enamel demineralization were determined. Biofilms of Streptococcus mutans [ S. mutans ] served as caries-positive control. Biofilms of S. sanguinis forming on enamel for 12 and 16 h showed higher demineralization than those formed during 8 h, but lower than S. mutans biofilms, regardless of the initial biofilm formation time. No differences were detected in the biofilm properties among the different biofilm formation times tested for S. sanguinis . Increased enamel initial biofilm formation time by S. sanguinis appears to induce a cariogenic potential, but lower than S. mutans .
Dental Caries; Dysbiosis; Symbiosis; Streptococcus sanguis; Streptococcus mutans; Dental Enamel
The biofilms were initially allowed to develop for different times on dental enamel and were treated with 10% sucrose solution, three times a day, for 5 min each time, for 5 days [120 h]. The pH of the culture medium was measured at 32 h and then twice a day. S. mutans biofilms in 10% sucrose solution and 0.9% NaCl represent caries-positive and caries-negative control, respectively. Each point represents the average of two independent experiments conducted three times [n = 6]. The error bars show the SD. Different letters represent statistically significant differences [p < 0.05].
For each enamel slab covered by S. sanguinis biofilms, surface hardness [SH] was measured before and after each experimental phase as a % of surface hardness loss [%SHL]. S. mutans biofilms in 10% sucrose and 0.9% NaCl represent caries-positive and caries-negative control, respectively. Each bar represents the average of two independent experiments conducted three times [n = 6]. The error bars show the SD. Different letters in each bar represent statistically significant differences [p < 0.05].
Representative sample of enamel slabs exposed to S. mutans biofilms during 8 h of initial formation under 10% sucrose. Light blue arrows indicate enamel demineralization [caries-like lesion formation] in the center of the slab and the covered edge used as sound enamel control. The picture was obtained through a polarized light microscope at 5x magnification.