In vivo virulence analyses of Streptococcus mutans lytTS genes and operon dltABCD and modulation thereof by targeted therapy

Abstract

Dental caries is a biofilm-dependent disease. The construction of the biofilm depends on the formation of the extracellular matrix (ECM). Exopolysaccharides (EPS) are indispensable for the construction of the MEC and 3D structuring. In addition, extracellular DNA (eDNA) and Lipoteichoic Acids (LTA) are found in high amounts in the ECM. Streptococcus mutans orchestrates the construction of the biofilm via gene expression: EPS are synthetized by enzymes encoded by gtfs genes, mainly by gtfB (water insoluble EPS), lytTS genes are associated with eDNA while the operon dltABCD genes encode proteins involved in LTA metabolism. In vitro studies performed with knockout mutants demonstrated that: the absence of the gtfB gene reduced the production water insoluble EPS in single- and mixed-species biofilms; the absence of lytTS genes induced greater release of eDNA; while the lack of genes dltAD genes increased LTA in the ECM. Release of eDNA and LTA by S. mutans is induced by sucrose, starch and high acidity. Thus, eDNA, LTA and EPS acting together intervene in the microbial population dynamics, composition and structure of the ECM. Therefore, the objectives of the present study are: 1) analysis of the roles of the lytT and dltA genes in the development and severity of carious lesions in vivo; 2) evaluation of the functions of lytTS and dltAD genes on oxidative stress and virulence in systemic infections in vivo; and 3) evaluation of agents to inhibit the lytTS and dltAD genes and its products, in addition to EPS production and assembly. The study will provide knowledge of roles of eDNA and LTA in biofilm construction and in virulence potential. In addition, it will to guide the use of specific agents for prevention of cariogenic biofilms. (AU)