To evaluate the ability of the broad-spectrum lantibiotic, lacticin 3147, to prevent Streptococcus mutans biofilm formation and disrupt existing biofilms. Minimum inhibitory concentrations (MIC) and minimum biofilm inhibitory concentrations of purified lacticin 3147 were determined using a microdilution method. Lacticin 3147 effectively inhibited planktonic Strep. mutans, with MIC of 1.9-3.8 μmol l(-1). Time-kill kinetic studies confirmed that lacticin 3147 exhibited bactericidal activity against Strep. mutans at 38 μmol l(-1) (or 10× MIC). The effect of lacticin 3147 on biofilm formation and reduction was also determined. Exposure to 6.3-μmol l(-1) lacticin 3147 (2× MIC) resulted in substantial reductions in Strep. mutans biofilm formation while lacticin 3147 was less effective against 1-day-old biofilms. Culture-based analyses revealed that lacticin 3147 (50 μmol l(-1)) significantly inhibited Streptococcus spp. present in human saliva (P < 0.05) with an approximate 4-log reduction in viability compared with the control. These results indicate that lacticin 3147 may be an effective therapy against Strep. mutans and was shown to substantially attenuate its ability to form a biofilm. Lacticin 3147 has the potential to be a useful adjunct to traditional oral therapeutic approaches in addition to its use as a bioactive ingredient for food applications.