Impact of regulatory cross-talk on the pathophysiology of emergent acapsular group A streptococcus

点击翻译按钮获取中文摘要

PROJECT SUMMARY The hyaluronic acid capsule of the major human pathogen group A Streptococcus (GAS) has classically been considered essential to infectivity. GAS is divided into emm types based on variation in the emm gene that encodes for the cell-surface, anti-phagocytic M protein. It has recently been appreciated that GAS strains from emm types lacking capsule are increasingly causing serious human infections to the point where some 30% of invasive GAS isolates are acapsular. How acapsular GAS causes infection is not currently known although it has been postulated that acapsular GAS strains elaborate high levels of a key cytotoxin, streptolysin O (Slo). Contrary to this conjecture, we have found that multiple acapsular emm types do not produce high levels of Slo, and thus the long term goal of our research is to elucidate the mechanistic basis of acapsular GAS pathophysiology. Through a comparative genomics approach, we have identified that acapsular GAS emm types have distinct compositions of the promoters of mga and emm which encode the key transcriptional regulator multi-gene activator (Mga) and M protein, respectively. Moreover, we have discovered that the control of virulence (CovRS) two-component gene regulatory system specifically impacts mga and emm transcript levels in acapsular relative to encapsulated GAS. These, and other, findings set the stage for this proposal which seeks to test the hypothesis that mga and emm promoter composition are critical to the infectivity of acapsular GAS by allowing for regulation by CovRS, which is critical for GAS to sense and respond to host signals. In specific aim 1, we will determine how variation in mga and emm promoters of acapsular GAS compared to encapsulated GAS alters the composition of the cell surface of acapsular emm4 and emm89 strains in response to the human antimicrobial peptide LL-37. We will also assess the impact of mga and emm promoter composition on acapsular GAS adherence to human epithelial cells and human extracellular matrix components, survival in human blood, resistance to phagocytosis, and virulence in a mouse model. In specific aim 2, we will determine if the changes observed in the mga and emm promoters of acapsular GAS allow for direct regulation by CovR and is the mechanism by which CovS inactivation influences mga and emm transcript levels. We will investigate in vivo interaction of CovR with mga and emm promoters and attempt to identify promoter regions that are key to CovR-based regulation using a luciferase based reporter system. We also will assess whether CovR directly represses emm in acapsular GAS independent of Mga. Completion of the research outlined herein will significantly augment understanding of the molecular mechanisms underlying the emergence of acapsular GAS which are a major cause of GAS infection yet remain poorly understood relative to encapsulated strains.