Investigation of the regulatory mechanism for the production of a human specific cytolysin, a crucial factor for the infectivity of Streptococcus intermedius

点击翻译按钮获取中文摘要

Streptococcus intermedius secretes intermedilysin(ILY), which is a major virulence factor of this pathogen. We showed that the disruption of lacR in an ILY low-producing strain (PC574) led to higher hemolytic activity, increased transcription of ily and higher cytotoxicity against HepG2 cells, when compared to the parental strain. The direct binding of LacR within the ily promoter region was observed by a DNA probe pull-down assay. Adding galactose or lactose into the medium increased the amount of ILY secreted by PC574 cells.Furthermore, we studied the lacR nucleotide sequences and the hemolytic activity of 50 strains isolated from clinical infections and 7 strains isolated from dental plaque. Thirteen strains isolated from clinical infections showed high ILY production and 9 strains had one or more point mutations and/or an insertion mutation in LacR, which caused the decline in its function.