Theses and Dissertations at Montana State University (MSU)
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Item The Staphylococcus aureus two-component system, SAER/S, modulates host mediators of inflammation to enhance pathogenesis(Montana State University - Bozeman, College of Agriculture, 2013) Watkins, Robert Lee; Chairperson, Graduate Committee: Jovanka Voyich-Kane; Kyler B Pallister and Jovanka M Voyich were co-authors of the article, 'The SAER/S gene regulatory system induces a proinflammatory cytokine response during Staphylococcus aureus infection' in the journal 'PLoS one' which is contained within this thesis.; Oliwia W Zurek, Kyler B Pallister and Jovanka M Voyich were co-authors of the article, 'The SAER/S two-component system promotes interferon-gamma in neutrophils during invasive Staphylococcus aureus infection' submitted to the journal 'Microbes and infection' which is contained within this thesis.; Oliwia W Zurek, Kyler B Pallister and Jovanka M Voyich were co-authors of the article, 'The SAER/S virulence system promotes interferon-gamma to enhance Staphylococcus aureus skin disease in an interleukin-17-dependent manner' submitted to the journal 'Journal of infectious diseases' which is contained within this thesis.Methicillin-resistant Staphylococcus aureus (MRSA) is an opportunistic pathogen that causes diseases ranging from superficial skin infections to life-threatening invasive disease. The emergence of community-associated MRSA has caused concern, as these infections appear in healthy individuals. Increasing prevalence of antimicrobial resistance warrants the development of alternative methods of combating infections. Modulating the host immune response during infection has shown promise in research settings, but has fallen short of application in the clinic. Characterizing how Staphylococcus aureus (S. aureus) influences host mediators of inflammation is an essential step for understanding S. aureus pathogenesis and could lead to the development of novel therapies, including immuno-modulation. Previous studies demonstrated the SaeR/S two-component system of S. auerus strongly regulates exoprotein production and is essential for full virulence of this pathogen. However, the mechanisms behind the role(s) of SaeR/S in mediating pathogenesis are incompletely defined. To that end, this investigation examined the role SaeR/S in impacting host inflammatory responses during both invasive and superficial S. aureus infections. Using mutant S. aureus strains with deleted saeR/S (DeltasaeR/S), these studies show that SaeR/S is critical for promoting pathogen survival, dissemination and host mortality during peritonitis. Pro-inflammatory cytokines, such as interferon-gamma (IFNgamma), tumor necrosis factor-alpha and interleukin (IL)-6 were significantly reduced in mice infected with DeltasaeR/S. IFNgamma transcriptional activation and protein expression were significantly induced by saeR/S during skin and invasive infections. Interestingly, neutrophils were identified as the predominant source of saeR/S-induced IFNgamma expression during early S. aureus peritonitis. Robust saeR/S-influenced IFNgamma production prompted further studies investigating the role of this cytokine during S. aureus infections. IFNgamma-deficient (GKO) mice were protected during invasive infection with wild-type S. aureus as reduced bacterial burdens and reduced host cellular cytotoxicity were observed. GKO mice were protected against wild-type S. aureus skin challenge in an IL-17-dependent manner. Interestingly, both normal and GKO mice exhibited similar pathologies when infected with DeltasaeR/S during invasive and superficial infections, suggesting that IFNgamma and IL-17 impact saeR/S-mediated pathogenesis and that in the absence of saeR/S, these cytokines are inconsequential in mediating immunity. Collectively, these studies suggest that saeR/S promotes a deleterious IFNgamma response that enhances S. aureus pathogenesis.Item Insights into the ArlR/S mediated pathogenesis of Staphylococcus aureus(Montana State University - Bozeman, College of Agriculture, 2013) Meyer, Susan Irene; Chairperson, Graduate Committee: Jovanka Voyich-Kane; Tyler K. Nygaard, Meet Patel, and Jovanka M. Voyich were co-authors of the article, 'The ArlR/S two-component signal transduction regulatory system is essential to the pathogenesis of Staphylococcus aureus' in the journal 'Microbes and infection' which is contained within this thesis.Staphylococcus aureus (S. aureus) is a gram-positive pathogen capable of causing a wide range of disease from relatively simple soft tissue infections to severe life-threatening disease like sepsis and endocarditis. Historically, most S. aureus infections were associated with healthcare settings and a majority of cases were seen in patients with compromised immune systems. In the past decade, however, infections caused by S. aureus have become more common in healthy individuals. These community-associated strains are an even bigger problem because a large percentage are resistant to antibiotics and are have an incredible ability to incur antibiotic resistance. The ability of this bacterium to subsist and thrive in a wide range of environmental conditions is partly due to the pathogen's use of two-component signal transduction gene-regulatory systems that have the ability to sense external conditions and regulate gene transcription appropriately. This study investigates the role of one of these two-component regulatory systems, ArlR/S. An isogenic deletion mutant of the arlR/S operon was created and was tested in several in vitro assays as well as in vivo murine models of infection. Using in murine models of soft tissue infection and invasive infection, it was determined that arlR/S is important to the virulence of S. aureus. A murine model of dissemination showed that S. aureus dissemination is altered with the deletion of the ArlR/S two-component regulatory system. To determine whether the decreased pathogenicity was caused by a change in the interaction between S. aureus and immune cells of the body, in vitro assays with human whole blood and human PMNs were performed with both S. aureus and bacterial supernatants. Interestingly, no differences were seen between the wild type S. aureus and the mutant in these assays. An oligonucleotide microarray was performed and showed strong regulation of ebh (ECM-binding protein homologue), which codes for the giant staphylococcal surface protein (GSSP). Together, this study demonstrates the importance of arlR/S to the regulation of ebh and to the virulence of S. aureus in a PMN-independent manner.