Contributions of the fatty acid kinase system beyond exogenous fatty acid uptake in Enterococcus faecalis

Enterococcus faecalis is a commensal of the gastrointestinal tract of mammals but can found in a range of environments including the bloodstream during infection and the vagina as a causative agent of aerobic vaginitis. These environments contain host-derived free fatty acids that can be used in membrane synthesis by E. faecalis through its Fatty Acid Kinase (Fak) system. While work in other species have shown contributions of the Fak system in pathogenesis, little is known how it impacts the colonization and survival of E. faecalis in various host environments. Using E. faecalis OG1RF and OG1RF derivatives deleted for multiple fakB genes, I demonstrated that the Fak system contributes to growth in bile, a component found within the native environment of the intestine, as well as contributed to membrane fluidity when cells are grown in human serum. Some of these impacts appear to be due to the presence of host-derived unsaturated fatty acids, oleic and linoleic acids. I further demonstrate that the Fak system contributes to E. faecalis colonization in a murine vaginal model. Strains deleted for one or multiple fakB genes were reduced in number within reproductive tissues. However, I noted that this reduction may not be due to an immune response determined via Enzyme-Linked Immunosorbent Assays (ELISA). Further analyses suggest that this reduced survival is likely not due to sensitivity to hydrogen peroxide, which is often produced during an inflammatory response. Preliminary in vitro data does suggest that sensitivity to cationic antimicrobial peptides may contribute to poor survival. The experiments performed herein show potential roles of the Fak system in vaginal ascension to the uterus in a murine model, modulating sensitivity to cationic antimicrobial peptides, and maintaining membrane fluidity when exogenous fatty acids are present. Furthermore, this work provides a strong foundation and rationale for further experimentation in the role of the Fak system in enterococcal pathogenesis.