Paradoxical Change in the Gastric Microbiome Structure in the Helicobacter pylori-related Advanced Gastric Mucosal Atrophy

Objective: Risk of Helicobacter pylori ( H. pylori )-related gastroduodenal diseases is influenced by the degree of chronic gastritis, while other microbes reside in gastric mucosa may be relevant to this process. This study aimed to characterize the microbiome composition in the gastric mucosa, especially with an attempt to its correlation with histologic and serological degrees of H. pylori -related gastritis. Methods: Among 182 cancer-free patients, bacterial communities of the gastric mucosa in the antrum were examined using 16S rRNA sequencing. The result was correlated with clinicopathological characteristics, histologic and serological degrees of H. pylori -related gastritis. Results: Bacterial alpha diversity measures were significantly lower in H. pylori clinical test positives compared with that in the negatives. Lower bacterial alpha diversity measures were also associated with degree of histologic gastritis in the antrum, while rather higher bacterial alpha diversity measures were correlated with degree of serological gastritis. The multiple regression analysis demonstrated that histologic gastritis (active gastritis, atrophy) was significantly associated with lower Shannon index (t=−4.37, P <0.0001), an indicator for bacterial alpha diversity. Inversely, serological gastritis (serum pepsinogen 3+) was also associated with higher Shannon index (t=2.98, P <0.0001). In the specific bacteria, higher abundances of Bacillus, Actinobacillus , and Streptococcus were associated with degree of serological gastritis. Conclusions: Our findings showed paradoxical change in the microbiome structure in the development of severe gastric atrophy that may be associated with progression of gastric atrophy and gastric cancer risk. The study was not registered as the clinical trial because of the retrospective observational study.