Hydrolyzed Ce(IV) salts limit sucrose-dependent biofilm formation by Streptococcus mutans

Several studies have focused on the antimicrobial effects of cerium oxide nanoparticles (CeO2-NP) but few have focused on their effects on bacteria under initial biofilm formation conditions. Streptococcus mutans is a prolific biofilm former contributing to dental caries in the presence of fermentable carbohydrates and is a recognized target for therapeutic intervention. CeO2-NP derived solely from Ce(IV) salt hydrolysis were found to reduce adherent bacteria by approximately 40% while commercial dispersions of "bare" CeO2-NP (e.g., 3 nm, 10-20 nm, 30 nm diameter) and Ce(NO3)3·6H2O were either inactive or observed to slightly increase biofilm formation under similar in vitro conditions. Planktonic growth and dispersal assays support a non-bactericidal mode of biofilm inhibition active in the initial phases of S. mutans biofilm production. Human cell proliferation assays suggest only minor effects of hydrolyzed Ce(IV) salts on cellular metabolism at concentrations up to 1 mM Ce, with less observed toxicity compared to equimolar concentrations of AgNO3. The results presented herein have implications in clinical dentistry.