Bacteriocin susceptibility and production in Streptococcus mutans

Objectives: In oral cavity, many kinds of bacterial species coexist, and form indigenous microflora. Under the restricted environment, bacteria affect each other to survive and grow. It is well known that many bacteria produce bacteriocin to interfere with the growth of the other bacteria. In this study, we evaluated the growth inhibitory activity among oral streptococci. Especially, we investigated the association of Streptococcus mutans two-component system (TCS) with bacteriocin production and susceptibility to bacteriocin produced by other oral streptococci. Methods: Sixteen sets of TCS mutants were constructed using S. mutans UA159 strain by an allelic exchange mutagenesis method. To evaluate susceptibility of bacteriocin produced by oral streptococci, competition assay was performed. The ability of bacteriocin production in TCS mutants was also evaluated. Results: We found that several streptococci produced bacteriocin although susceptibility to bacteriocin was different among streptococcal species. S. mutans was sensitive to the bacteriocin produced by S. sanguinis, S. gordonii and S. mitis. This inhibitory effect of S. sanguinis and S. gordonii was only found in aerobic condition, but the effect of S. mitis was found in aerobic and anaerobic condition. As the result, 2 TCS mutants showed the increased susceptibility and 1 mutant showed the decreased susceptibility to the bacteriocin produced by S. sanguinis and S. gordonii. The ability of bacteriocin production of 1 mutant was decreased. Conclusions: Together with previous reports, our results indicate that bacteriocin produced by S. sanguinis and S. gordonii is hydrogen peroxide (H2O2). We demonstrated that 3 TCSs in S. mutnas were associated with susceptibility to H2O2. 1 TCS was associated with bacteriocin production. In conclusion, S. mutans has several TCSs related to bacteriocin. Since S. mutans coexists with other bacteria including other streptococci in dental plaque, S. mutans may utilize several TCSs to sense or produce bacteriocin and survive environment.