Browsing by Subject "Streptococcus pyogenes"
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Item CcpA-Mediated Carbon Catabolite Repression of Virulence in the Group A Streptoccus(2008-09-18) Kinkel, Traci L.; McIver, Kevin S.The group A streptococcus (GAS) is a strict human pathogen, which causes a broad spectrum of diseases ranging from the self-limiting diseases such as pharyngitis and impetigo to the more severe invasive disease such as necrotizing fasciitis. The coordinate expression of a wide array of virulence factors in response to the changing host environment represents a key step in the ability of the GAS to mediate disease in the human host. The present study investigates the role of the primary mediator of sugar metabolism regulation, carbon catabolite control protein (CcpA), in the regulation of virulence of the GAS. A putative CcpA-binding site or catabolite response element (cre) was identified upstream of the promoter for the virulence gene regulator, Mga. CcpA was shown to specifically bind to this cre, and activate the transcription of mga. In addition, both transcription of mga and expression of Mga were reduced in a ccpA mutant strain; however, the expression of the Mga-regulated genes were not affected. Additional studies analyzing the role of CcpA in pathogenesis of the GAS, showed a "hypervirulent" phenotype in the absence of CcpA using two mouse infection models. Microarray analysis of the delta ccpA strain determined that CcpA significantly represses the expression of saga, the gene encoding the potent cytolysin, streptolysin S (SLS). Moreover, hemolytic activity due to SLS was increased in the delta ccpA strain, and expression from Psaga demonstrated strong catabolite repression during growth in glucose compared to sucrose. Furthermore, purified GAS CcpA was shown to bind directly to the cre present in Psaga. The role of SLS in the increased pathogenesis of the delta ccpA strain was investigated by the creation of a double mutant strain, which lacks the ability to secrete SLS. Importantly, systemic infection of mice with the delta ccpA sagB double mutant resulted in complete attenuation of virulence and determined that the increased SLS expression is responsible for the "hypervirulent" phenotype in the absence of CcpA. Overall, these results have demonstrated a strong link between sugar metabolism regulation and virulence gene expression in the GAS.Item Use of an Animal Model of Group A Streptococcal Infection to Identify Factors Important for Virulence(2006-12-15) Leday, Temekka V.; McIver, Kevin S.The Group A Streptococcus (GAS) is a strict human pathogen responsible for a broad assortment of diseases ranging from pharyngitis (strep throat) and impetigo to necrotizing fasciitis (flesh eating disease) and streptococcal toxic shock syndrome (STSS). Virulence of the GAS is multifactorial, as it possesses an array of virulence factors regulated in a coordinated fashion by a complement of transcriptional regulators. A mouse model of streptococcal invasive skin infection was used to identify unknown factors important in GAS virulence. The first section of this study used this model to assess the effect of a mutation in the response regulator gene spt10R on virulence in vivo. The spt10R mutation was subsequently discovered to have a polar effect on the downstream ß-galactosidase BgaA. Disruption of bgaA was shown to lead to an attenuation of virulence in the mouse model as well as a reduction in the production of the cysteine protease SpeB. Complementation of the spt10R/bgaA double mutant with bgaA restored the expression of speB to wild type levels. A microarray analysis of the spt10R/bgaA mutant revealed significant transcriptional changes in genes involved in virulence and carbohydrate metabolism. In addition, spt10SR and bgaA were found to be part of a four-gene operon that is repressed by the CovR virulence regulator. A second avenue of study comparing various sequenced strains in the invasive skin infection model revealed a hypervirulent M3 strain MGAS315. This hypervirulence phenotype was lost upon in vitro passage similar to the passages used during directed mutagenesis of the strain. There was no remarkable phenotypic difference between MGAS315 and its passage-attenuated derivative in vitro. However, transcriptome and proteome analysis at mid- and late-logarithmic phases of growth revealed potential contributors to the hypervirulence phenotype. Upon passage through mice, the passage-attenuated strain was able to revert towards the high virulence phenotype. Overall, an animal model of streptococcal invasive skin infection was useful in the study and identification of factors important for virulence and may provide insight into the interaction of the GAS with its host.