Sustainable inhibition efficacy of liposome-encapsulated nisin on insoluble glucan-biofilm synthesis by Streptococcus mutans

Context: Dental caries are an infectious oral bacterial disease caused by cariogenic streptococci. These streptococci inhabit dental biofilms which comprise insoluble glucans. Objective: To prevent dental caries, nisin, a suitable agent active against Gram-positive bacteria, was examined in vitro for its ability to suppress insoluble glucan-biofilm synthesis by cariogenic streptococci. Materials and methods: To investigate glucan-biofilm synthesis by a typical cariogenic streptococcus, Streptococcus mutans 10449, the naked form of nisin was loaded onto a 96-well microplate in vitro model. To prolong the efficacy of nisin as a preventive agent, liposome-encapsulated nisin (nisin-liposome) was examined for its ability to inhibit the synthesis of glucan-biofilms on microplates. Results: Naked nisin (100 pmol) completely suppressed insoluble glucan-biofilm synthesis by S. mutans 10449 following 1 h cultivation in 96-well microplates. The concentration of nisin-liposome required for the efficacious inhibition of glucan-biofilm synthesis was four times lower than that of naked nisin following 2 h cultivation. In particular, nisin-liposome (30 pmol nisin equivalent) prolonged the inhibitory activity of nisin against glucan-biofilm synthesis by S. mutans 10449 for up to 6 h, while naked nisin (30 pmol) gradually lost this inhibitory activity over the same period. In vitro release assay of nisin from the liposome showed that 76% nisin was released within 6 h. Discussion and conclusion: The findings indicate the usefulness of nisin-liposome for the sustained release of nisin. Thus, nisin-liposome could play a potential role in preventive medicine as an inhibitor of the glucan-biofilm synthesis.