Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 8 2 2016 05 14 93 100 EN Azam Aliasghari Department of Biology, Faculty of Sciences, University of Isfahan, Iran. Mohammad Rabbani-Khorasgani Department of Biology, Faculty of Sciences, University of Isfahan, Iran. Sedigheh Vaezifar Department of Medical Engineering, Payame Noor University, Iran. Fateh Rahimi Department of Biology, Faculty of Sciences, University of Isfahan, Iran. Habibollah Younesi Department of Environmental Science, Faculty of Natural Resources, Tarbiat Modares University, Tehran, Iran. Maryam Khoroushi Dental Materials Research Center & Department of Operative Dentistry, School of Dentistry, IsfahanUniversity of Medical Sciences Isfahan , Iran. 2015 11 07 2016 04 16 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. https://ijm.tums.ac.ir/index.php/ijm/article/view/788 https://ijm.tums.ac.ir/index.php/ijm/article/download/788/578