Effects of Chitosan on Mutans Streptococci Biofilms

Methods: Minimum bactericidal concentrations (MBCs) of chitosans in 1% acetic acid against S. mutans and S. sobrinus were determined by the broth microdilution method. Biofilms of the mutans streptococci were established in the 96-well polystyrene microtiter plate. An Anti-biofilm formation was determined by incubating mutans streptococci with different concentrations of the chitosans in 5% (w/v) sucrose. Then the biofilms were quantified by staining with crystal violet, de-staining with 95% ethanol and measured with a microplate reader at 595 nm. The effect of chitosans on biofilms vitality was determined by treating 4-hour mutans streptococci biofilms with 2 % chitosan for 5, 15, and 30 min. The survival cells in treated-biofilm were determined by plate counting and calculated to percentage in comparison with untreated control. Listerine® mouthwash was used as a positive control in all experiments.

Results: The MBCs of the 100 kDa- and 390 kDa-chitosan against S. mutans were 0.06% and 0.25%, respectively, whereas those against S. sobrinus were 0.5%. Both molecular-weight-chitosans at 1% and 0.5% concentrations could inhibit biofilm formation of S. mutans, ranging from 83 to 89% and of S. sobrinus ranging from 86 to 95%. The susceptibility of the 4-hour biofilm was time-dependent. There were only 55% S. mutans survival after exposure to 100 kDa- chitosan for 30 min. There were no bacterial survival and biofilm formation in positive control.

Conclusions: The study showed that chitosans has antibacterial and anti-biofilm activity against mutans streptococci. Thus, chitosan could be used as a promising agent for controlling dental caries.