Different response to amine fluoride by Streptococcus mutans and polymicrobial biofilms in a novel high-throughput active attachment model

Background/Aims: The antimicrobial resistance of microorganismsin biofilms and the polymicrobial interactions inthese biofilms that modulate resistance require novel strategies
to evaluate the efficacy of caries-preventive compounds.The current study aimed to evaluate the effects of acaries-preventive agent in Streptococcus mutans and polymicrobial
biofilms.
Methods: We developed a novel highthroughput active attachment model. The model consisted of a custom-designed lid containing glass discs that fit on top of standard 24-well plates. Biofilms were formed using either S. mutans C180-2 or saliva. At the end of biofilm formation (up to 96 h) the biofilms were treated with amine fluoride (AmF) solutions. The viability of the biofilms was determined by CFU counts, and metabolic activity was measured via lactate production.
Results: The effect of AmF on the viability
of the polymicrobial biofilms was significantly less than that on the S. mutans biofilms, indicating a higher resistance in the complex biofilms. Both types of biofilms became
more resistant to AmF with age. The higher resistan of the polymicrobial biofilms was not reflected in metabolic activity; in dose-response experiments AmF reduced lactate
production in both types of biofilms to the same extent. Moreover, the age-induced increased resistance in the polymicrobial biofilms was less pronounced in terms of the inhibition of metabolic activity.
Conclusions: This study clearly shows that when evaluating the efficacy of caries-preventive compounds it is essential to use appropriate polymicrobial
biofilm models, and more importantly that efficacy needs to be judged based on the eduction of acid formation (i.e. cariogenic potential) as well as on bacterial viability.