An in vitro synergetic evaluation of the use of nisin and sodium fluoride or chlorhexidine against Streptococcus mutans.

The objective of this study is to investigate the synergetic action between nisin and sodium fluoride or chlorhexidine against Streptococcus mutans, a primary cariogenic pathogen. In the antibacterial assay, a synergetic effect on S. mutans was found between nisin and sodium fluoride, but there was no interaction between nisin and chlorhexidine by the checkerboard, the fractional inhibitory concentration (FIC) and the fractional bactericidal concentration (FBC) tests. S. mutans survival rates showed a significant decline after treatment with a combination of nisin and sodium fluoride in a time-kill study. Scanning electron microscopy showed that the damage to S. mutans with the combined nisin and sodium fluoride treatment was the most severe among all of the different single and combined antimicrobial treatments. Furthermore, in the antibiofilm test, nisin in combination with sodium fluoride produced a stronger bactericidal effect on a S. mutans biofilm for 4 h and 16 h compared with sodium fluoride alone by confocal laser scanning microscopy. Nisin in combination with sodium fluoride exerted a high bactericidal effect on S. mutans and thereby has the potential to be used as an effective drug combination to prevent dental caries.