Inactivation of streptococcus mutans genes lytST and dltAD impairs its pathogenicity in vivo

Streptococcus mutans orchestrates the development of a biofilm that causes dental caries in the presence of dietary sucrose, and, in the bloodstream, S. mutans can cause systemic infections. The development of a cariogenic biofilm is dependent on the formation of an extracellular matrix rich in exopolysaccharides, which contains extracellular DNA (eDNA) and lipoteichoic acids (LTAs). While the exopolysaccharides are virulence markers, the involvement of genes linked to eDNA and LTAs metabolism in the pathogenicity of S. mutans remains unclear. In this study, a parental strain S. mutans UA159 and derivative strains carrying single gene deletions were used to investigate the role of eDNA (ΔlytS and ΔlytT), LTA (ΔdltA and ΔdltD), and insoluble exopolysaccharides (ΔgtfB) in virulence in a rodent model of dental caries (rats) and a systemic infection model (Galleria mellonella larvae). Fewer carious lesions were observed on smooth and sulcal surfaces of enamel and dentin of the rats infected with ΔlytS, ΔdltD, and ΔgtfB (vs. the parental strain). Moreover, strains carrying gene deletions prevented the killing of larvae (vs. the parental strain). Altogether, these findings indicate that inactivation of lytST and dltAD impaired S. mutans cariogenicity and virulence in vivo111CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ141896/2017-5; 311707/2016-5; 311707/2016-5; 141896/2017-52014/05423-0; 2017/00753-0; 2014/05423-0; 2014/01723-9; 2016/08021-5; 2017/00753-0This research was supported by a research grant from the São Paulo Research Foundation (FAPESP, grant number 2014/05423-0 to M.I.K.) and scholarships (FAPESP, grant numbers 2017/00753-0 to M.C.C.P., 2014/01723-9 to A.R. F.C., and 2016/08021-5 to L.S.L.). In addition, the authors thank the National Council for Scientific and Technological Development (CNPq) for providing scholarship (grant number 141896/2017-5 to M.C.C.P for five months). M.I.K. also received funding from CNPq (grant #311707/2016-5). The authors are grateful to Eliane Franco, José Carlos, Josy G. Lazarini, and Bruno Dias Nani for their technical support. The present study is part of the PhD thesis by M.C.C.