The Prevalence and the Pathophysiological Role of Non-Helicobacter Pylori Helicobacter Spp. in Well-defined Gastric Diseases and (Pre-) Malignancies

The goal of this clinical trial is to discover the prevalence of NHPH bacteria (Non-Helicobacter pylori Helicobacter species) in patients with one of the following conditions: 1. Functional dyspepsia following the Rome IV criteria 2. Active chronic gastritis, non-H. pylori induced atrophic gastritis, intestinal metaplasia and non-H.pylori gastric dysplasia 3. Gastric cancer, including siewert type 2 and 3 esophagastric junction cancers In addition, patients undergoing bariatric surgery are included as a control group. This study will be conducted using a prospective analysis in the three targeted study populations. Biopsy specimens routinely taken during the medical procedure or via the resected material in patients belonging to the target groups will be used. Exclusion criteria: * Patients with a history of H. pylori infection diagnosed by serology, on gastric biopsy, by breath test or on antigen test in stool samples. * Pregnancy. * Underage patients (\< 18 years).