Identification of the role of the sal locus in streptococcus pyogenes virulence during host-pathogen interactions

The pathogenesis of Streptococcus pyogenes is due to its ability to overcome and adapt to the harsh environment created by the host immune response. The focus of this project was the SalKR two-component regulatory system, which facilitates bacterial adaptation by responding to environmental signals during host pathogen-interactions. The first goal of this project was to determine a role in virulence for the SalKR regulatory system. The complete deletion of the salKR genes in the wild type S. pyogenes strain HSC5 produced a highly attenuated mutant in a Zebrafish infection model. The ΔsalKR mutant appeared to lose the ability to survive in the blood stream, which consequently inhibited systemic dissemination to the spleen. The attenuation of the ΔsalKR mutant in the blood stream was due to its sensitivity to intracellular and extracellular killing by neutrophils. This was most likely a consequence of the high susceptibility of the ΔsalKR mutant to cell lysis by lysozyme, attributable to the differences observed in cell wall modification between the wild type and the mutant. Our data suggests that this modification is SalKR dependent. The SalKR system was also involved in a cellular adaptation process while residing intracellularly in macrophages resulting in greater resistance to neutrophil killing. The second goal of this study was to identify the regulation of salKR gene expression. Transcriptional analysis of the sal locus revealed that expression of the salKR genes are governed by two promoters, the salA promoter and the salKR promoter. SalR regulates its own promoter by binding directly to repression sites identified both upstream and downstream of the salKR promoter. The SalA peptide, encoded by the salA gene at the 5\u27 end of the sal locus also affected salKR promoter activity. Both the salA and salKR promoters showed increased promoter activity during exposure to human serum. Taken together, the data suggested the importance of the SalKR two component system in virulence and its requirement during host-pathogen interactions