Antimicrobial activity of silver nanocomposite against oral micro-organisms

Objectives: Silver-nanocomposites (AgNC) offer molecular versatility as antimicrobial agents for dental applications. This study aimed to assess the potential of a prototype AgNC to reduce the bio-burden within the oral cavity.
Methods: Aqueous suspensions of AgNCs were prepared by a micelle templated synthesis, using sodium dodecylsulfate . Seven bacterial species were assessed for sensitivity; Staphylococcus oxford, Escherichia coli, Pseudomonas aeruginosa, Streptococcus mutans, S. mitis, S.gordonii and Enterococcus faecalis. The well diffusion assay was used to to assess inhibition of bacterial growth by AgNCs. Real-time bactericidal assays were performed at a range of AgNC concentrations over 3 hrs, using the BacLight fluorescent viability stain. Viability (fluorescence) was measured at 15 min intervals in a microtitre plate reader maintained at 37 °C.
Results: Previous well diffusion assays demonstrated that growth for all bacteria tested was inhibited at silver concentrations of 7- 10 µg/ml. Subsequent minimum bactericidal concentration (MBC) determinations by fluorescence viability indicated that for S.gordonii, E.coli and S.mutan 27.95 µg Ag/ml killed ≥90% within 15 minutes; for S.mitis, E.faecalis, P.aeruginosa and S.oxford a concentration of 55.9 µg Ag/ml killed ≥70% within 15 minutes. A concentration-dependent antimicrobial effect was observed across all bacterial. Baclight live/dead stain was shown to be a good quantitative technique for establishing the efficiency of the supplied AgNC product. AgNCs were composed of 400-800 nm assemblies of uniform-sized (50-70 nm) micelle aggregates (determined by electron microscopy) with shelf-life of > 1 year .
Conclusions: We have demonstrated the use of a potential oral medicament, displaying superior oligodynamic properties, at effective silver concentrations achieving bacterial killing in a 15 min time frame. These promising antibacterial results support the potential use of AgNCs for treatment of oral infections.