Approximately two billion people are colonized with Staphylococcus aureus worldwide, but only a minority of these individuals will develop invasive infections. This application focuses on the role of nitric oxide (NO*), a molecular mediator that modulates bacterial physiology by targeting protein thiols and metal centers, during nasal colonization by S. aureus. We will test the hypothesis that NO* inhibits virulence and regulates microaerobic respiration in S. aureus. Our preliminary observations suggest that NO* is a critical determinant of whether S. aureus exists in a stable commensal relationship with the host or becomes an invasive pathogen.
Our specific aims are to: (1) Assess the mechanism of S. aureus virulence gene inhibition by NO* - We have found that NO* inhibits the expression of virulence genes required for invasive infection. Genetic and biochemical approaches will determine how exogenous NO* inhibits virulence gene expression, focusing on AgrA, MgrA, SarR and SarS, four central transcriptional regulators that are S- nitrosylated by NO*. A novel murine nasal colonization model will be used to determine the effects of host-derived NO* on S. aureus virulence gene expression in vivo. (2) Analyze the regulation of S. aureus microaerobic physiology and colonization by NO* - S. aureus produces its own NO* by expressing an enzyme (saNOS) related to mammalian NO* synthases. We have discovered that saNOS is required for redox sensing during the microaerobic transition from aerobic respiration to nitrate respiration and for nasal colonization in mice.
This aim will use expression and biochemical assays to test a novel mechanistic model in which bacterial-derived NO* diverts electron transport to nitrate reductase when O2 concentrations are limiting. Our mouse model will be used to assess the contribution of host- and bacterial-derived NO* to S. aureus colonization in vivo. These studies will establish NO* as a critically important signaling molecule that allows S. aureus to adapt to oxygen-limited conditions within the host environment while maintaining it in a commensal state by modulating virulence gene expression.

Public Health Relevance

The body's immune cells produce nitric oxide to limit the growth of microorganisms. This research project analyzes the mechanisms by which nitric oxide regulates metabolism and gene expression in the important human pathogen Staphylococcus aureus and thereby plays a crucial role in its ability to colonize a host and cause invasive disease. Such studies will inform efforts to devise novel strategies for the prevention and treatment of infections.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Host Interactions with Bacterial Pathogens Study Section (HIBP)
Program Officer
Huntley, Clayton C
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University of Washington
Schools of Medicine
United States
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Urbano, Rodolfo; Karlinsey, Joyce E; Libby, Stephen J et al. (2018) Host Nitric Oxide Disrupts Microbial Cell-to-Cell Communication to Inhibit Staphylococcal Virulence. Cell Host Microbe 23:594-606.e7
Kinkel, Traci L; Ramos-MontaƱez, Smirla; Pando, Jasmine M et al. (2016) An essential role for bacterial nitric oxide synthase in Staphylococcus aureus electron transfer and colonization. Nat Microbiol 2:16224
Fang, Ferric C; Frawley, Elaine R; Tapscott, Timothy et al. (2016) Bacterial Stress Responses during Host Infection. Cell Host Microbe 20:133-43