Biofilm Inhibitory Effect of Natto on Clinical Isolates of Streptococcus mutans

Abstract

　Streptococcus mutans is a major cause of dental caries. The water-soluble fraction of natto exhibits biofilm inhibitory effects against S. mutans. S. mutans is genetically and phenotypically diverse, and its biofilm-forming ability differs at the strain level. This study investigated the biofilm inhibitory effects of natto against nine S. mutans strains, with different genotypes and biofilm-forming abilities, isolated from the human oral cavity. We evaluated the biofilm inhibitory ability of natto produced on a laboratory scale. γ-Polyglutamic acid, the main component of stringiness in natto products, and the protease activity were identical between laboratory-produced natto and commercial products. The water-soluble fraction obtained from natto dose-dependently inhibited biofilm formation in all the tested S. mutans strains. Moreover, the biofilm inhibitory effect of commercially available subtilisin NAT, the major protease found in natto and also known as nattokinase, was similar to that of natto extract. These results suggest that natto has biofilm inhibitory effects against several S. mutans strains and can be used as a preventive food of dental caries.