Effects of non-albicans Candida species on biofilm formation and acidogenicity of dual-species biofilms and on cariogenic virulence gene expression of streptococcus mutans

Abstract

Early childhood caries is a common oral disease found in children which could affect their general health. Streptococcus mutans is an important cariogenic pathogen since it possesses cariogenic properties, which are acid production, acid tolerance and biofilm formation. Recent studies showed that Candida albicans, which is frequently found together with S. mutans in plaques of children with dental caries, enhances cariogenicity. At the same time, increasing prevalence of non-albicans Candida species (NACs) in children and immune-compromised patients has been reported. Therefore, this study aims to investigate the effects of NACs when co-cultured with S. mutans on cariogenic properties and virulence gene expression of S. mutans. The results showed that C. albicans and NACs, especially Candida tropicalis, increased biofilm mass and cell viability of dual species biofilm, but did not increase acid production. For S. mutans gene expression, the genes related to exopolysaccharides synthesis (gtfBCD), sugar transportation (scrAB) and sugar utilization (pdhA and pfl) were up-regulated in dual species biofilm when co-culture with C. albicans, C. tropicalis and Candida krusei. In contrast, the expression levels of genes related to acid stress tolerance (atpD and fabM) in all dual-species biofilm were similar to S. mutans in single-species biofilm. In addition, the expression of genes involved in the signal transduction system (ciaRH) were upregulated in dual-species biofilms of S. mutans and C. albicans or NACs, except C. dubliniensis. In conclusion, the presence of NACs, especially C. tropicalis and C. krusei, could enhance cariogenic virulence factors of S. mutans similarly to C. albicans.