N. Oetiker, D. Bravo, J.M. Pérez-Donoso
Universidad Andres Bello,
Chile
Keywords: oral health, copper nanoparticles, antimicrobial activity
Summary:
Tooth decay has been recognized as the principal cause of bacterial infection and chronic disease affecting humans produced by the fermentation of diet carbohydrates mainly mediated by the pathobionts Streptococcus mutans and Lactobacillus spp. In a healthy oral stage, these pathological conditions are managed by beneficial bacteria such as S. salivarius and S. sanguinis, which naturally control the presence of pathobionts. Currently, the main control and treatment for this disease are based on prevention with hygiene and proper oral care. Metal nanoparticles have emerged as a promising oral antibacterial and anti-plaque formation element in the last decade due to their high bactericidal and bacteriostatic capacity. In the present work, we determined the effect of three types of copper nanoparticles (NP-Cu0, NP-Cu2O and NP-CuO) on the growth, viability, and biofilm formation of two bacteria associated with caries formation (S. mutans and L. rhamnosus) and two bacteria associated to dental health stage (S. salivarius and S. sanguinis). Obtained results indicate that Cu NPs affect these bacteria differently, being the oxides the most toxic. S. sanguinis are the most tolerant to NP-Cu0, NP-Cu2O, and NP-CuO (MIC 1000, 1000, and 800 µg / mL, respectively), and L. rhamnosus the most sensitive (800, 300, and 200 µg / mL, respectively). Because NP-CuO mostly affects pathobiont bacteria we compared their effect on bacterial viability. Our results indicated that S. mutans is the most sensitive Streptococcus bacteria with a bactericidal concentration of 500 µg / mL of NP-CuO. Since biofilm formation is the principal condition for caries and S. mutans is the most important demineralizing teeth bacteria within the oral biofilm, we analyzed the effect of Cu NPs in their biofilm formation on the teeth surface using scanning electron microscopy. Interestingly, all Cu NPs analyzed affected the formation of oral biofilm of this pathobiont and produced a detachment of the mature biofilm at 200 µg / mL. On the other hand, although NP-CuO do not greatly affect the viability or growth of S. mutans, a low amount of this impacts negatively biofilm formation on the tooth surface. Based on these results and thinking in a possible biotechnological application, we analyzed the cytotoxicity of all NP-Cu in epithelial oral cells, determining low toxicity at the concentrations affecting bacterial pathogens. Since the formation of caries is a result of microbiome dysbiosis within the oral cavity, it is important to maintain the healthy mouth stage. This is the first work analyzing the effect of NP-Cu on beneficial and pathogenic oral bacteria. Our results revealed that bacteria associated with healthy and pathogenic oral health have different sensitivity to NP-Cu, with oxides presenting the highest toxicity for pathogenic bacteria. Importantly, S. mutans biofilm is strongly affected at low concentrations of all NP used. Our results reveal the potential of Cu oxide NPs to be used as a treatment for the control of biofilm formation and growth of important pathobiont with minimal effects on beneficial oral bacteria.