Effects of heat-inactivated Bifidobacterium BB12 on cariogenicity of Streptococcus mutans in vitro

Since some probiotic bacteria are cariogenic themselves, their suitability for caries management is questionable. Inactivated bacteria or their supernatants have been found to exert probiotic effects, whilst having several advantages compared with living bacteria. We hypothesized that viable and heat-inactivated Bifidobacterium animalis BB12 reduces the cariogenicity of Streptococcus mutans (SM) in vitro.

We assessed mono- and mixed species biofilms of SM and viable or heat-inactivated BB12. Biofilms were grown in a continuous-culture-system under cariogenic conditions on smooth proximal enamel or cavitated dentine. For each of eight experimental subsets (4 biofilms×2 hard-tissue conditions), a total of 32 specimens was used. After 10 days, bacterial numbers of 12 biofilms per group were analysed, and all specimens submitted to transversal microradiography.

Mineral loss was higher in cavitated dentine than smooth enamel for all biofilms (p<0.001, t-test). BB12-monospecies biofilms induced significantly less mineral loss than SM in both enamel (p<0.05) and dentine (p<0.001). Viable BB12 did not significantly reduce cariogenicity of SM (p>0.05), whilst heat-inactivated BB12 decreased cariogenicity of SM in dentinal cavities (p<0.01). Bacterial numbers were higher on dentine than enamel (p<0.05), but not significantly influenced by biofilm species (p>0.05).

Heat-inactivated BB12 reduced the cariogenicity of SM in dentinal cavities in vitro. Inactivated probiotics might be suitable for caries control.