the effect of gold nano particles with different sizes on streptococcus species

Statement of the problem: streptococcus mutans, streptococcus sanguinis, and strepto-coccus salivarius are most common etiologic bacteria for dental caries. different sizes of gold nanoparticles may have different antibacterial effects on these species. purpose: this study aimed to compare the antibacterial effect of chlorhexidine and three sizes of gold nano particles (25, 60, 90nm) against clinical and standard strains of strepto-coccus mutans, streptococcus sanguinis, and streptococcus salivarius. materials and method: in this cross-sectional study, the specimens were collected from 75 children aged 3-5 years old. antibacterial effect of chlorhexidine and three sizes of gold nano particles (25, 60, 90nm) were investigated by evaluating the minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) against three bacterial strains. results: the mic and mbc of gold nanoparticles with different sizes against streptococ- cus mutans, streptococcus sanguinis, and streptococcus salivarius were statistically different. the mic and mbc of smaller gold nano particles (25nm) were significantly lower (p<0.001) than larger ones. patient-derived bacteria had significantly higher values of mic and mbc in comparison to standard species (p<0.001). conclusion: the results of this study confirmed the significant size-dependency of gold nano particles for antibacterial activity. as the size of gold nano particles decrease, the antibacterial properties enhance.