| Helicobacter pylori causes peptic ulcer disease, gastritis, and gastric cancer and is a major health concern due to its increasing antibiotic resistance. H. pylori must resist acidic pH, oxidative and nitrosative stress, and bile salts to persist in the host. Understanding these mechanisms of resistance will reveal targets for sorely needed anti- Helicobacter therapies. The mechanisms of H. pylori resistance to bile salts are undefined. H. pylori steals cholesterol from host cell membranes, incorporates the cholesterol onto its membrane, and glycosylates the cholesterol. The only known enzyme in this pathway is cholesteryl glycosyltransferase (Cgt), which glycosylates the incorporated cholesterol. H. pylori utilizes free cholesterol or host cell-derived cholesterol to protect itself from bile salts. Furthermore, Cgt is not responsible for this cholesterol-dependent resistance. The exact mechanism of cholesterol-dependent protection has yet to be elucidated. H. pylori hefABC encodes a putative bile salt efflux pump. hefC encodes an inner membrane protein transporter, HefC, which is required for H. pylori resistance to high bile salt concentrations. However, cholesterol is still able to protect the hefC mutant H. pylori from low bile salt concentrations. The involvement of HefC in bile salt resistance was confirmed by inhibiting bile salt efflux in a HefC-dependent manner and by restoring bile salt resistance to the hefC mutant by complementation. Interestingly, cholesterol uptake is delayed in the hefC mutant, indicating HefC may play a role in cholesterol uptake or incorporation. The hefC mutant is attenuated at early time points in gerbils and displays a reduced ability to induce inflammation in gerbils compared to wild type. In addition, bile salt-fed gerbils had elevated stomach bile salt levels and decreased colonization of H. pylori. Understanding mechanisms of H. pylori bile salt resistance will aid the field in determining how H. pylori is able to adapt to a constantly changing environment and persist in the host. The studies in this dissertation have identified and characterized two novel mechanisms of bile salt resistance in H. pylori: 1) cholesterol-dependent and 2) HefC-mediated. |
