Inhibitory effects of Streptococcus salivarius K12 on formation of cariogenic biofilm

BACGROUND/PURPOSE: Streptococcus salivarius (S. salivarius) K12 is known to be a probiotic bacterium. The purpose of this study was to investigate anti-cariogenic effects of S. salivarius K12 on cariogenic biofilm. MATERIALS AND METHODS: S. salivarius K12 was cultured in M17 broth. The antimicrobial activity of spent culture medium (SCM) against Streptococcus mutans was investigated. S. salivarius K12 was co-cultivated with S. mutans using a membrane insert. When the biofilm was formed using salivary bacteria and S. mutans, the K12 was inoculated every day. The biomass of biofilm was investigated by a confocal laser scanning microscope. Also, bacterial DNA from the biofilm was extracted, and then bacteria proportion was analyzed by quantitative PCR using specific primers. The expression of gtf genes of S. mutans in the biofilm with or without S. salivarius K12 was analyzed by RT-PCR. RESULTS: The SCM of S. salivarius K12 inhibited the growth of S. mutans. Also, S. salivarius K12 reduced S. mutans growth in co-cultivation. The formation of cariogenic biofilm was reduced by adding S. salivarius K12, and the count of S. mutans in the biofilm was also decreased in the presence of S. salivarius K12. gtfB, gtfC, and gtfD expression of S. mutans in the biofilm was reduced in the presence of S. salivarius K12. CONCLUSION: S. salivarius K12 may inhibit the formation of cariogenic biofilm by interrupting the growth and glucosyltransferase production of S. mutans.