Pathogenicity of Streptococcus mutans and Candida albicans interaction in oral biofilm

Abstract

Dental caries is a worldwide public health problem. This disease is caused by a pathogenic biofilm. Candida albicans has been found in association with Streptococcus mutans in biofilms from early childhood caries lesions. An in vitro model demonstrated that biofilms formed by S. mutans and C. albicans present higher amount of extracellular matrix (ECM), rich in exopolysaccharides, especially insoluble polysaccharides synthetized by S. mutans exoenzymes (vs. S. mutans single species biofilm). This type of ECM results in niches within the biofilms, allowing acids produced by microorganism (during dietary carbohydrate metabolism) be confined at the interface biofilm/teeth surfaces, leading to acid-dissolution of teeth (demineralization - i.e., caries lesions). In fact, the colonization of rats´ oral cavity by both species lead to increased number of caries lesions, with augmented severity. However, it is still unknown the mechanisms of both species that work synergistically to increase biofilm's pathogenicity. Therefore, the aim of this project is to evaluate which mechanisms of S. mutans (besides the production of exopolysaccharide-rich ECM) and of C. albicans contribute to the augmentation of biofilm's pathogenicity. Mixed and single-species biofilms will be formed in presence of sucrose, which will be analyzed using biochemical (biomass, ECM composition), microbiological (colony forming unit - CFU determination), microscopic (biofilm structure), and gene expression (i.e., RT-qPCR of genes from metabolic pathways from both species) methods. The research outcomes will bring new insights about the pathogenesis of biofilms formed by a bacterium and a fungus, which could help designing desperately needed preventive and therapeutic strategies. (AU)