Regulation of S.pyogenes virulence determinants

The resurgence of serious group A beta-hemolytic streptococci (GAS) infections since the early 1980s is mainly characterized by diseases like severe soft-tissue invasion, necrotizing fasciitis and toxic-shock-like syndrome. Despite the availability of modern medicine and several antibiotic treatment options invasive severe GAS disease still kills 20-50% of the patients within 72 to 96 hours. The increased severity of streptococcal infections since the beginnings of the 1980s is probably at least in parts a result of the increased virulence of streptococcus itself. Among the many factors that have been made responsible for the enhanced virulence of the organism, the streptococcal pyrogenic exotoxins (SPEs) constitute prime candidates for the particular pathogenesis of severe invasive GAS disease. Transcriptional analysis of one of the major toxins, SPE-A, revealed the identification of two strain-specific, cell density-dependent variations in speA transcription and demonstrated the presence of a broadly specific autoinducer in GAS culture supernatants, also capable of heterologous activation. The finding that the autoinducer is not encoded by the phage carrying speA and is able to induce a number of streptococcal exoproteins, including the superantigens SPE-C and SPE-F, suggests that a global regulatory system controls streptococcal superantigens, and possibly other exoproteins. Biochemical characterization of the autoinducer indicates that the substance is a modified peptide, different from the recently identified putative signaling peptide encoded by the pel locus. Moving speA into Staphylococcus aureus brings the streptococcal superantigen under the control of the staphylococcal global regulator agr, indicating an evolutionary relationship among streptococcal SPE-A and staphylococcal enterotoxins. The research I am proposing will focus on the identification of the autoinducer and its encoding gene. Further, we intend to identify further target genes of the autoinducer. The characterization of a putative receptor and the identification of inhibitior(s) of superantigen transcription are another focus of the proposal.

Most infections caused by group A beta-hemolytic streptococci (GAS) are localized to the skin and nasopharynx (strep throat), however, a small proportion involves severe invasive disease, giving rise to streptococcal toxic shock syndrome and necrotizing fasciitis. Among the many factors that have been implicated in the pathogenesis of severe invasive streptococcal disease, the importance of streptococcal pyrogenic exotoxins is the least undisputed one. Streptococcal pyrogenic exotoxins belong to the family of bacterial superantigens, which are characterized by their capacity to stimulate T-lymphocytes without prior antigen processing, leading to massive cytokine release by immune cells, followed by systemic inflammatory reactions resulting in fever and capillary leakage, leading to hypotension, shock, multi-organ failure and death. The resurgence of serious GAS infections during the past decade has been associated with the expression of streptococcal pyrogenic exotoxins. To identify factors that are responsible for the increased aggressiveness of GAS infections we studied expression characteristics of two streptococcal pyrogenic exotoxins, and tried to identify novel regulatory mechanisms involved in the regulation of virulence factors. In our study, we have established the role of a GAS gene locus, called pel (pleiotropic effect locus), as a positive regulator of important streptococcal virulence factors. We could demonstrate that the pel-encoded regulator is the untranslated pel RNA, a mechanism which has been so far unknown for GAS. Further, it could be shown that the synthesis of pel RNA is induced by conditioned media, a phenomenon we could also assign to two pyrogenic exotoxins. In case of GAS it seems that at least two distinct soluble factors are in charge of activating the expression of the above mentioned exotoxins. We believe that the identification and characterization of signal transduction pathways responsible for the in vitro and in vivo regulation of key streptococcal virulence factors will contribute significantly to the understanding of streptococcal pathogenicity. Since pel RNA can be considered as a global regulator of GAS virulence this mechanism could be exploited in the future for the development of novel antimicrobial agents.