RESUMEN
Streptococcus constellatus is a member of the Anginosus group streptococci (AGS) and primarily inhabits the human oral cavity. S. constellatus is composed of three subspecies: S. constellatus subsp. constellatus (SCC), S. constellatus subsp. pharyngis and the newly described subspecies S. constellatus subsp. viborgensis. Although previous studies have established that SCC contains ß-haemolytic strains, the factor(s) responsible for ß-haemolysis in ß-haemolytic SCC (ß-SCC) has yet to be clarified. Recently, we discovered that a streptolysin S (SLS) homologue is the ß-haemolytic factor of ß-haemolytic Streptococcus anginosus subsp. anginosus (ß-SAA), another member of the AGS. Furthermore, because previous studies have suggested that other AGS species, except for Streptococcus intermedius, do not possess a haemolysin(s) belonging to the family of cholesterol-dependent cytolysins, we hypothesized that, as with ß-SAA, the SLS homologue is the ß-haemolytic factor of ß-SCC, and therefore aimed to investigate and characterize the haemolytic factor of ß-SCC in the present study. PCR amplification revealed that all of the tested ß-SCC strains were positive for the sagA homologue of SCC (sagA(SCC)). Further investigations using ß-SCC strain W277 were conducted to elucidate the relationship between sagA(SCC) and ß-haemolysis by constructing sagA(SCC) deletion mutants, which completely lost ß-haemolytic activity. This loss of ß-haemolytic activity was restored by trans-complementation of sagA(SCC). Furthermore, a co-cultivation assay established that the cytotoxicity of ß-SCC was clearly dependent on the presence of sagA(SCC). These results demonstrate that sagA(SCC) is the factor responsible for ß-SCC ß-haemolysis and cytotoxicity.
