Autoimmune Gastritis and Gastric Microbiota.

Autoimmune atrophic gastritis is an organ-specific immune-mediated condition characterized by atrophy of the oxyntic mucosa. Autoimmune atrophic gastritis (AIG) is characterized by a progressive loss of acid-secreting parietal cells leading to hypo-achlorhydria. Due to this peculiar intra-gastric environment, gastric microbiota composition in individuals with autoimmune atrophic gastritis was first supposed and then recently reported to be different from subjects with a normal acidic healthy stomach. Recent data confirm the prominent role of Helicobacter pylori as the main bacterium responsible for gastric disease and long-term complications. However, other bacteria than Helicobacter pylori, for example, Streptococci, were found in subjects who developed gastric cancer and in subjects at risk of this fearful complication, as well as those with autoimmune gastritis. Gastric microbiota composition is challenging to study due to the acidic gastric environment, the difficulty of obtaining representative samples of the entire gastric microbiota, and the possible contamination by oral or throat microorganisms, which can potentially lead to the distortion of the original gastric microbial composition, but innovative molecular approaches based on the analysis of the hyper-variable region of the 16S rRNA gene have been developed, permitting us to obtain an overall microbial composition view of the RNA gene that is present only in prokaryotic cells.