Pre-Treatment With Arginine Inhibits Sucrose-Induced pH Drop in Saliva-Derived Biofilm

Objectives: Dental caries can be described as a dysbiosis of the oral microbial community. Dietary sucrose increases caries risk through induction of acid production by acidogenic bacteria, which in turn promotes demineralization of enamel and further selects for acidogenic and aciduric bacterial species. Arginine has been shown to induce alkali production in oral bacteria, which may inhibit caries formation. The aim of the current study was to evaluate the response of ex vivo-derived oral bacterial communities to pre-treatment with arginine and subsequent sucrose exposure.
Methods: Pooled saliva collected from caries-free (CF) and caries-active (CA) patients was used to create CF and CA in vitro communities. CF and CA communities were grown as biofilms in 24-well plates in chemically-defined media at a starting pH of 5.5 or 7. Arginine (75mM) was added at time 0, followed by the addition of 0.5% sucrose after 6, 20, 48, or 54 h. At each time point, pH was measured and biofilms were collected for 16S sequencing and GC-MS metabolomics analysis. Results were compared to media-only, sucrose-only, and arginine-only controls.
Results: The addition of sucrose at time 0 led to a pH drop to 4.5 after 6 h regardless of starting pH (5.5 or 7), in both CA and CF biofilms. pH did not drop in biofilms pre-incubated with arginine 20 or 48 hours prior to the addition of sucrose (pH=8 at 48 h). 16S sequencing revealed a shift in the microbial community structure of biofilms pre-incubated with arginine, specifically an increase in arginine-metabolizing species and a decrease in acid-producing S. mutans. GC-MS analysis revealed an increase in arginine secondary metabolites by the arginine-treated biofilms, indicating active uptake and metabolism.
Conclusions: Overall, results suggest that treatment with arginine may protect against sucrose-induced acid generation through re-engineering the oral microbial community.