evaluation of antibacterial efficiency of chitosan and chitosan nanoparti- cles on cariogenic streptococci: an in vitro study

background and objectives: the most prevalent and worldwide oral disease is dental caries that affects a significant pro- portion of the world population. there are some classical approaches for control, prevention and treatment of this pathologic condition; however, the results are still not completely successful. therefore new methods are needed for better management of this important challenge. chitosan is a natural and non-toxic polysaccharide with many biological applications, particu- larly as an antimicrobial agent. chitosan nanoparticle is a bioactive and environment friendly material with unique physico- chemical properties. the aim of the present study was to investigate the antimicrobial effect of chitosan and nano-chitosan on the most important cariogenic streptococci. materials and methods: for evaluation of antimicrobial effect of chitosan and nano-chitosan against oral streptococci broth micro-dilution method was carried out for four bacterial species; streptococcus mutans, streptococcus sobrinus, streptococ- cus sanguis and streptococcus salivarius. also the effect of these materials on adhesion of above bacteria was evaluated. one-way anova and post hoc tukey test were used for statistical analysis. results: the mics of chitosan for s. mutans, s. sanguis, s. salivarius and s. sobrinus were 1.25, 1.25, 0.625 and 0.625 mg/ ml, respectively. the mic of chitosan nanoparticle for s. mutans, s. salivarius and s. sobrinus was 0.625 mg/ml and for s. sanguis was 0.312 mg/ml. chitosan and chitosan nanoparticles at a concentration of 5 mg/ml also reduced biofilm forma- tion of s. mutans up to 92.5% and 93.4%, respectively. conclusion:   t e results of this study supported the use of chitosan and chitosan nanoparticles as antimicrobial agents against cariogenic streptococci.