Assessing the impact of curcumin on dual-species biofilms formed by Streptococcus mutans and Candida albicans

Streptococcus mutans and Candida albicans are often isolated from plaques associated with early childhood caries. However, there are limited studies examining how these microorganisms interact with one another and how best to manage them. Recent studies have shown that curcumin (CUR), a natural compound, has the potential to independently control both of these microorganisms. The purpose of this study was to investigate how S. mutans and C. albicans respond in mono- and dual-species biofilms challenged with CUR. Quantitative biofilm biomass and viability were first evaluated and supported by live-dead PCR to assess biofilm composition. Confocal laser scanning microscopy (CLSM) was used to evaluate the exopolysaccharide (EPS) content and thickness of the biofilms, and the structure of the biofilms and morphology of the cells were observed by scanning electron microscopy (SEM). Quantitative real-time PCR (qRT-PCR) was applied to assess relative gene expression. The 50% minimum biofilm eradication concentration (MBEC₅₀ ) of CUR against S. mutans and C. albicans was 0.5 mM. The biomass and viability decreased after treatment with CUR both in dual-species biofilms and in mono-species biofilm. CUR inhibited S. mutans and C. albicans in both mono- and dual-species biofilms. Streptococcus mutans was more sensitive to CUR in dual-species biofilm than in mono-species biofilms, whereas C. albicans was less sensitive in dual-species biofilms. EPS production was decreased by CUR in both mono- and dual-species biofilms, which coincided with the downregulation of glucosyltransferase and quorum sensing-related gene expression of S. mutans. In C. albicans, the agglutinin-like sequence family of C. albicans was also downregulated in dual-species biofilms. Collectively, these data show the potential benefit of using a natural antimicrobial, CUR, to control caries-related dual-species plaque biofilms.