Interaction between LL-37 and CsrRS of group A Streptococcus

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DESCRIPTION (provided by applicant): Group A Streptococcus (GAS, also known as Streptococcus pyogenes) is a common human pathogen, most frequently causing pharyngitis or "strep throat." However, severe invasive infections like necrotizing fasciitis and toxic shock syndrome are also caused by this organism, leading to its nickname in the lay press - "flesh-eating bacteria." This work will help explain the process by which a microbe in the throat can invade and cause life-threatening illness. Previous studies found that GAS alter transcription of multiple virulence factors in response to the human cathelicidin, LL-37, an antimicrobial peptide. A membrane-bound sensor kinase (CsrS) and its cytoplasmic response regulator (CsrR) appear to drive this reaction. This application aims to examine the role of LL-37 in stimulating an invasive phenotype in GAS. We will focus on the interaction of GAS with two host cell types commonly encountered early in infection: keratinocytes and macrophages. We will examine the role that LL-37 and CsrRS play in GAS's ability to avoid internalization and killing. Overall, these studies will examine a fascinating evolutionary interaction between a human pathogen and the innate immune system, offering new insights into the pathogenesis of GAS infections. PUBLIC HEALTH RELEVANCE: The public health burden of GAS infection remains high. Sequelae of infection, including rheumatic heart disease, continue to plague especially developing areas, where prompt antibiotic therapy is unavailable. Additionally, there has been a rise in invasive GAS infections as a new, more virulent strain has spread around the globe. For these reasons, improving our understanding of the earliest stages of human infection will be essential to battling this common yet evolving pathogen.