Inhibitory Effect of Bacillus velezensis on Biofilm Formation by Streptococcus mutans

Abstract

Streptococcus mutans plays a key role in the development of dental caries and promotes the formation of oral biofilm produced by glucosyltransferases (GTFs). Bacillus velezensis K68 was isolated from traditional fermented foods and inhibits biofilm formation mediated by S. mutans. Gene amplification results demonstrated that B. velezensis K68 contained genes for the biosynthesis of 1-deoxynojirimycin (1-DNJ), a known GTF expression inhibitor. The presence of the GabT1, Yktc1, and GutB1 genes required for 1-DNJ synthesis in B. velezensis K68 was confirmed. Supernatant from B. velezensis K68 culture medium inhibited biofilm formation by 84% when S. mutans was cultured for 48 h, and inhibited it maximally when 1% glucose was added to the S. mutans culture medium as a GTF substrate. In addition, supernatant from B. velezensis K68 medium containing 3 ppb 1- DNJ decreased S. mutans cell surface hydrophobicity by 79.0 {+/-} 0.8% compared with that of untreated control. The supernatant containing 1-DNJ decreased S. mutans adherence by 99.97% and 98.83% under sugar-dependent and sugar-independent conditions, respectively. S. mutans treated with the supernatant exhibited significantly reduced expression of the essential GTF genes gtfB, gtfC, and gtfD compared to that in the untreated group. Thus, B. velezensis inhibits the biofilm formation, adhesion, and GTF gene expression of S. mutans through 1- DNJ production.\n\nIMPORTANCEDental caries is among the most common infectious diseases worldwide, and its development is closely associated with physiological factors of bacteria, such as the biofilm formation and glucosyltransferase production of Streptococcus mutans. Biofilms are difficult to remove once they have formed due to the exopolysaccharide matrix produced by the microorganisms residing in them; thus, inhibiting biofilm formation is a current focal point of research into prevention of dental caries. This study describes the inhibitory properties of Bacillus velezensis K68, an organism isolated from traditional Korean fermented foods, against biofilm formation by S. mutans. Herein, we show that B. velezensis inhibits the biofilm formation, adherence to surfaces, and glucosyltransferase production of S. mutans.