Copper Nanoparticles Have Differential Effect on Supragingival Oral Bacteria

Objectives: Recently, cooper containing nanoparticles have been used as antimicrobial agents against different pathogenic organisms and during the last years have been incorporated on dental materials.
In the present work, we studied the effect of Cu⁰, Cu₂O, and CuO nanoparticles on the growth, viability, and biofilm formation of two caries-associated pathobionts (S. mutans and L. rhamnosus), and two commensal microorganisms (S. salivarius and S. sanguinis).
Methods: We use Cu⁰, Cu₂O, and CuO nanoparticles of 30-40 nm size. We test their antibacterial properties by MIC assays and CFU counting, and antibiofilm activity of nanoparticles in vitro, using crystal violet, and ex vivo, using electronic microscopy.
Results: Our results show that Cu⁰, Cu₂O, and CuO NPs differentially affect bacteria being S. sanguinis the most tolerant, and L. rhamnosus the most sensitive. Interestingly, CuO NPs exhibited higher toxicity over pathobionts than commensal bacteria. This phenomenon was also observed when the bactericidal effect of CuO NPs was evaluated, resulting in a stronger bactericidal effect (> 99.99 % dead of S. mutans and L. rhamnosus) compared to S. sanguinis (94 % dead). We also showed that Cu NPs decreased S. mutans biofilm formation. Interestingly, no effect over biofilm formation was observed in S. sanguinis exposed to Cu⁰, Cu₂O, and CuO NPs. In contrast, a higher adherence was determined on S. salivarius exposed to these Cu NPs. Then, we analyzed the effect of Cu NPs over biofilm formation on teeth crowns. Ex vivo assays showed that all Cu NPs diminished the biofilm formation and produced detachment of its mature biofilm.
Conclusions: To our knowledge, this is the first work analyzing the effect of NP-Cu on beneficial and pathogenic oral bacteria. Our results revealed that bacteria associated with health and pathogenicity have different sensitivity to Cu NPs, being the oxides the most toxic compounds for pathogenic bacteria.