Investigation on the mechanism for pathogenic evolution of Anginosus group streptococci focusing on their cytotoxic products

Anginosus group streptococci are opportunistic pathogens inhabiting in human oral cavity. In general, species belonging to this group had been recognized as low- or non-pathogenic species. However, the reports about pathogenic factor produced from the species in this group and about the relationship between diseases and the clinical isolation of Anginosus group streptococci have been increasing recently. So, it is thought that now will be the time to re-evaluate the real pathogenicity of this group. We have previously reported that the novel cytotoxic factor in β-hemolytic Anginosus group streptococci except for Streptococcus intermedius is a homolog of streptolysin S, a peptide hemolysin secreted from such as Pyogenic group streptococci. Interestingly, the genomic locus of the gene cluster for streptolysin S homolog production, designated as sag operon, proposed an idea that the pathogenic evolution of opportunistic low- or non-pathogenic Anginosus group streptococci may be induced by the acquisition of a genetic material(s) encoding pathogenic factor(s). In this study, the possibility of pathogenic evolution in Anginosus group streptococci was investigated and discussed focusing on the possession of sag operon