Inhibitory effect of carboxylated nanodiamond on oral pathogenic bacteria Streptococcus mutans

BACKGROUND: Nanodiamonds (NDs) have been demonstrated to have bactericidal activity on several microorganisms and can be used in various kinds of dental materials. NDs are potential candidates for antibacterial dental materials. However, the possible inhibitory effect of NDs on oral pathogenic bacteria is largely unknown. This study was performed to investigate the inhibitory effects of carboxylated nanodiamond (cND) on Streptococcus mutans. METHODS: Fourier transform infrared spectroscopy was used to confirm carboxyl groups on the surface of commercial cND. The inhibitory effect of serially diluted cND on S. mutans was evaluated by spectrophotometry and plating methods. Escherichia coli was treated as a positive control in spectrophotometry. Chlorhexidine was used as a positive control in plating methods. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to confirm the antibacterial activity of cND. RESULTS: The results showed that cND exhibited a significant inhibitory effect on S. mutans. For S. mutans, the minimum inhibitory concentration was 4 μg/ml and the minimum bactericidal concentration was 16 μg/ml. SEM and TEM results indicated that cND functioned as an antibacterial agent, likely due to its ability to disrupt the cell membrane of S. mutans. CONCLUSION: In conclusion, these findings demonstrated an inhibitory effect of cND on S. mutans and suggest its use as a potential antibacterial dental material.