Statement of the Problem: Dental caries is considered as an important problem of public health in which Streptococcus mutans, Streptococcus sanguinis and Streptococcus salivarius have been verified as its most common etiologic bacteria.
Purpose: This study aimed to compare the antibacterial effect of chlorhexidine and three sizes of gold nano particle (25, 60, 90nm) against clinical and standard strains of Streptococcus mutans, Streptococcus sanguinis, and Streptococcus salivarius.
Materials and Method: The specimens were collected from 75 children aged 3-5 years old. These bacteria were detected by PCR and were exposed to three sizes of gold nano particle. Serial dilution method was used to compare their antibacterial efficacy. The effect of chlorhexidine and three sizes of gold nano particle were investigated by evaluating the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against three bacterial strains.
Results: The MIC and MBC of different sizes of gold nanoparticles against different bacteria were statistically different (p< 0.001). For Streptococcus mutans, Streptococcus sanguinis and Streptococcus salivarius, The MIC and MBC of all sizes of gold nano particles (25, 60, 90 nm) were significantly different (p<0.001). In comparison the MIC and MBC values of patient derived bacteria and standard species in all evaluated ones and all gold nano particle sizes, significant (p<0.001) differences were reported except the MIC and MBC of 60 and 90 nm gold nano particles for Streptococcus mutans and Streptococcus salivarius.
Conclusion: The results of this study confirmed the significant size-dependency of gold nano particles for antibacterial activity. As the size gold nano particles decrease, the antibacterial properties enhance.