Glucans effect antibody penetration of Streptococcus mutans biofilms

Objective: Glucans and fructans play a pivotal role in the pathogenesis of dental biofilms. In this study we examined the effect of glucans and fructans on antibody binding to, and penetration of biofilms. Materials & Methods: S. mutans GS5 (wild type), S. mutans V1741 (Glucan hyper-producing and FTF inactivated strain) and S. mutans V1995 (fructan hyper-producing and GTF inactivated) were grown as biofilms in 96-well clear bottom plates in BHI supplemented with sucrose. After fixation, biofilms were treated with Dextranase or Inulinase, and incubated with anti-S. mutans cell wall antibodies. Biofilm bacteria, and antibodies were flouroscently labeled by Propidium Iodide and Cy5^TM conjugated Goat Anti-Rabbit IgG, respectively. CSLM was used to establish antibody binding to, and penetration of the biofilms. Results: S. mutans cell wall specific antibodies bound to S. mutans biofilm in correlation with its glucan content: Biofilms composed of S. mutans V1741 bound more than twice as many antibodies compared to wild-type biofilm. In the absence of glucans (S. mutans V1995 biofilm), the antibody-bacterium ratio was 40 times higher than that of wild type biofilm, presumably due to increase in penetration of biofilm. Dextranase treatment of S. mutans V1741 biofilm caused a 36% reduction of the antibody-bacterium ratio, while in wild type the same treatment increased the ratio by 20% (relative to relevant biofilms not treated enzimatically). Antibody penetration of S. mutans V1741 biofilm was significantly less than penetration of wild type biofilm. Dextranase treatment improved antibody penetration of both glucan-producing biofilms. Conclusions: The total amount of antibody bound to biofilm, as well as the antibody-bacterium ratio, differed markedly among the various bacterial strains and enzymatic treatments. Glucans were found to have an inhibitory effect on antibody penetration of biofilm.