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Master of Science


Microbiology and Immunology


McGavin, Martin J.


Schulich School of Medicine and Dentistry


To colonize human skin and survive within abscesses, Staphylococcus aureus has evolved mechanisms to evade host innate defenses. USA300 has become the predominate community-acquired methicillin-resistant S. aureus (CA-MRSA) clone, which can be in part attributed to detoxification of unsaturated free fatty acids (uFFA) found in sebum and the nares. Our lab has previously identified the TetR family regulator FarR responsible for induction of the resistance-nodulation-division (RND) superfamily efflux pump FarE to promote efflux of toxic uFFA. However, RND family efflux pumps remain poorly characterized in Gram-positive species and the mechanism by which FarR regulates FarE has yet to be determined. Here, we demonstrate a predictive binding pocket in the final helix of the C-terminal ligand-binding domain and the potential for acyl-phosphates as an activating ligand of FarR through in silico techniques. Additionally, growth analyses demonstrate the sufficiency of naturally occurring amino acid variations in FarR to promote increased resistance to uFFA. However, these FarR variants did not promote increased resistance to alternative antimicrobials. These data further characterize the importance of RND family pumps in a Gram-positive background, while illuminating one mechanism by which the FarER system aids in antimicrobial fatty acid resistance.

Summary for Lay Audience

Staphylococcus aureus has been shown to asymptomatically colonize approximately 30% of healthy adults on the skin or in the nose. Subsequently, opportunistic infection by the colonizing strain can cause serious and invasive infection. The major cause of community-acquired infection is USA300, while the major cause of hospital-associated infection is USA100. Typically, acidification of the skin through the production of free fatty acids in sebum disrupts microbial membranes and causes bacterial death. However, S. aureus has gained methods for detoxification through free fatty acid export. Here, we further elucidate the mechanism by which the efflux pump FarE is modulated by the regulator FarR and demonstrate the impact of naturally occurring mutations in FarR on resistance to free fatty acids found on human skin. Overall, understanding the mechanism by which S. aureus resists immune defenses will aid in discovery of potential antimicrobial and vaccination targets.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Available for download on Saturday, June 01, 2024