The corruption of innate immunity by Streptococcus anginosus group

Abstract Streptococcus anginosus group (SAG), formerly known as Streptococcus milleri, consists of three distinct streptococcal species: Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius. SAG was considered as commensal bacteria of colon, oral cavity and vagina. Recent observation reported those bacteria as potent pathogens found in brain or liver abscess. Mechanism of SAG pathogenesis is still unknown, despite the strong set of clinical data. In our study, we determined the virulence of different SAG clinical isolates by examining the activity of hemolysins, DNAses and proteases. By using Dictyostelium discoideum as model for screening SAG virulence we selected a few high and low virulence strains out of 41 SAG isolates. Finally, we established and characterized the infection process of selected SAG strains by wax worm Galleria mellonella. Therefore, we aimed to characterize how those bacteria can interact with human innate immunity. In our experiments, using both human serum and whole blood we demonstrated, that these bacteria are resistant to killing by non-specific mechanisms of the immune response. Our studies have demonstrated that SAG have numerous virulence factors which differ among examined strains, and which allow bacteria to effectively colonize the human body and avoid elimination by the immune system. Supported by National Science Centre, Poland 2018/29/B/NZ6/00624