Microscale analyses of the effect of arginine on oral biofilms.

Objective: Arginine is a caries-preventive agent that modulates the microbial composition of dental biofilms and raises pH via bacterial ammonia production. The effect of arginine on biofilm pH has only been measured in bulk, and it is unknown how treatment affects microscale pH developments inside dental biofilms. Moreover, little is known about arginine's impact on the biofilm matrix. This study investigated the effects of arginine on biofilm pH, matrix architecture and microbial composition in a saliva-derived biofilm model.

Methods: 72-h biofilms were grown with or without sucrose, and arginine was either supplemented during growth or provided as pulsed treatment. pH was measured in different locations at the biofilm base using confocal-microscopy-based pH ratiometry. Matrix carbohydrates and extracellular DNA (eDNA) were assessed via fluorescence-lectin-binding-analysis and eDNA mapping. Microbial composition was determined by 16S rRNA gene sequencing.

Results: Arginine supplementation during growth considerably raised the biofilm pH, despite the presence of sucrose, and counteracted sucrose-induced shifts in microbial composition. Pulsed arginine treatment, in contrast, had little influence on microbial composition, but still a significant effect on biofilm pH. Importantly, arginine treatment increased the pH variance between different biofilm areas, suggesting that local factors in the biofilm microarchitecture modulate the treatment response. Lastly, arginine supplementation reduced the abundance of matrix carbohydrates, while increasing eDNA levels.

Conclusions: Arginine impacts biofilm pH at the microscale and changes the microbial and matrix composition in a saliva-derived biofilm model. Conclusions: Arginine exerts caries-preventive effects via multiple mechanisms, including modulations of biofilm pH and matrix microarchitecture.