Impact of Streptococcus salivarius K12 probiotic on pH and tooth enamel integrity in an in vitro oral biofilm system.

AIM: To evaluate the impact of an early exposure and a single re-administration of the probiotic Streptococcus salivarius K12 on pH dynamics, bacterial viability, and enamel surface hardness in a multispecies cariogenic biofilm over 12 days under the sucrose challenging conditions.

METHODS

Anaerobic co-cultures of five oral streptococcal species (S. mutans, S. sobrinus, S. sanguinis, S. mitis, and S. gordonii) were grown with or without S. salivarius K12 on bovine enamel specimens in artificial saliva (AS) in well plates at 37 °C. The static biofilm model was exposed daily to AS with 0.5% sucrose for 8 hours, followed by AS without sucrose for 16 hours. S. salivarius K12 was applied at initial inoculation and re-administered on day 3. Planktonic pH and colony-forming units (CFU/mL) were measured before each medium change. On day 12, enamel Martens hardness (HM), biofilm cell viability (CFU/mL), and extracellular matrix pH (C-SNARF-4 ratiometry) were assessed. Probiotic-only and AS-only conditions served as controls.

RESULTS

A single reapplication of S. salivarius K12 to the mixed cariogenic culture significantly reduced acidification by day 3-4 with pH values 5.9 ± 0.26 compared to 4.4 ± 0.06 in culture without probiotic. However, this effect diminished over time. By day 12, no significant differences in HM, extracellular biofilm pH, or CFU/mL were observed between probiotic-treated and untreated cultures.

CONCLUSIONS

Early exposure and a single re-administration of S. salivarius K12 can temporarily reduce acidification in artificial cariogenic biofilms, however repeated applications is necessary for lasting effects on enamel integrity and biofilm properties.