Carbohydrate Influence on Streptococcus mutans and Candida species Mixed Biofilms

Objectives: Studies show a synergistic pathogenic association between Streptococcus mutans (SM) and Candida albicans (CA) in the etiology of early childhood caries (ECC). In vitro studies of SM and CA dual-cultures demonstrate altered gene expression in comparison to mono-species cultures of SM or CA. Although CA is the most common Candida species isolated from the human oral cavity, a recently introduced Candida-selective and differential medium shows that other Candida species (CS) are also isolated from saliva and dental plaque. This study examines the effect of glucose or sucrose, as a carbon source, on biofilm formation by mono-species Candida and dual-species Candida-SM cultures.
Methods: Single CS and dual-species SM+CS cultures were grown in a semi-defined biofilm medium containing either glucose or sucrose. Four CS were utilized: CA, C. glabrata (CG), C. dubliniensis (CD), and C. tropicalis (CT). The 16 combinations were plated in quadruplicate (n=4) in a 96-well culture dish, then incubated at 37°C for 24 hours. Biofilms were stained with crystal violet and statistically analyzed (Mann-Whitney U test, Student’s t-test, p<0.05).
Results: In the mono-species Candida cultures, growth on sucrose, compared to glucose, significantly increased biofilm production of CA and CD. No significant difference in biofilm production was noted for CG or CT in the presence of either carbohydrate. For the Candida-SM dual-cultures, growth on sucrose, compared to glucose, increased CA-SM, CG-SM, and CD-SM biofilm production. Carbon source did not alter CT-SM biofilm production.
Conclusions: This study demonstrates that the more cariogenic sugar sucrose stimulates biofilm production of CA and CD when cultured with or without SM. Sucrose stimulates biofilm production of CG only when co-cultured with SM. CT, alone or in co-culture with SM, does not demonstrate differential biofilm production with glucose or sucrose. This study indicates that sucrose enhances SM and CS mixed biofilm formation, which may contribute to ECC development.