Antibacterial activity of high-molecular-weight and low-molecular-weight chitosan upon oral pathogens

One of the common oral bacterial infectious diseases is dental caries. Control of dental plaque formed by Streptococcus mutans and Streptococcus sobrinus leads to prevention and treatment of caries. Chitosan (1-4, 2-amino-2-deoxy-b-D-glucan), a deacetylated derivative from chitin, is an antimicrobial polysaccharide that exerts broad-spectrum activity against pathogenic bacteria and has been suggested as a preventive and therapeutic material for dental caries.The aim of this investigation is whether chitosan has effective antimicrobial and antibiofilm properties against common cariogenic microorganisms.The effect of 0.019-5 mg/ml of high-molecular-weight (HMW) and low-molecular-weight (LMW) chitosan on S. mutans and S. sobrinus was evaluated, and minimal inhibitory concentration (MIC) and minimal bactericide concentration (MBC) were determined. In addition, the effects of HMW and LMW of chitosan on bacterial adhesion to surfaces and biofilm formation were assayed by tube method.The results showed that chitosan is capable of inhibiting S. mutans and S. sobrinus growth (P = 0.001). MIC of HMW chitosan for S. mutans and S. sobrinus was 0.62 mg/mL and MIC of LMW chitosan for S. mutans and S. sobrinus was 0.62 mg/mL, 1.25 mg/mL, respectively. MBC of HMW chitosan for S. mutans and S. sobrinus was 1.25 mg/mL, respectively, and MBC of LMW chitosan for S. mutans and S. sobrinus was 1.25 and 2.5 mg/ml, respectively. On the other hand, HMW chitosan was more effective than LMW chitosan. In addition, S. mutans showed equal MIC and MBC values for both MWs chitosan, but S. sobrinus was more resistant to LMW chitosan. Regarding biofilm growth, chitosan inhibited S. mutans and S. sobrinus adhesion and biofilm formation. The results of tube test showed weak adherence and biofilm formation in concentration of 0.312 and 0.625 mg/ml, but 1.25 and 2.5 mg/ml concentrations of both MWs could completely inhibit biofilm formation.These results display the potential of chitosan to be used as an effective antibacterial and antibiofilm agent for oral hygiene and health care.