Gastric Microbiota and Gastric Diseases

Abstract

The stomach harbors a diverse microbiota, including Helicobacter pylori, which plays a crucial role in the development and progression of gastric diseases. In the healthy adult stomach, the predominant phyla include Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Fusobacteria, while at the genus level, Prevotella, Streptococcus, Veillonella, Fusobacterium, and Neisseria are most frequently detected. In the presence of H. pylori infection, the relative abundance of non-H. pylori bacteria decreases, leading to reduced α-diversity. As atrophic gastritis progresses and intestinal metaplasia develops, the gastric environment shifts toward hypochlorhydria, accompanied by a relative increase in oral and intestinal bacteria, further loss of microbial diversity, and activation of carcinogenesis-related pathways. Although successful H. pylori eradication therapy is associated with partial recovery of α-diversity, the gastric microbiota in adults does not fully normalize, and persistent dysbiosis may underlie the development of gastric cancer after eradication therapy. In autoimmune gastritis, achlorhydria and hypergastrinemia are associated with Streptococcus-dominant microbial profiles, and distinct microbial signatures have been reported in cases complicated by type I gastric neuroendocrine tumors. In gastric cancer, Lactobacillus is the most frequently detected genus. This genus exhibits a dual role in carcinogenesis, promoting tumor cell proliferation and angiogenesis through the production of lactic acid and N-nitroso compounds, while certain strains demonstrate antitumor effects. In addition to H. pylori, oral bacteria such as Fusobacterium nucleatum and Streptococcus anginosus have been identified as gastric cancer-associated microbes. Furthermore, in H. pylori-negative gastric MALT lymphoma, the involvement of non-H. pylori Helicobacter species is a critical issue in therapeutic strategies. Future studies should focus on the standardization of analytical methodologies for gastric microbiota and on elucidating causal relationships through animal models, interventional studies, and multi-omics integrative analyses. Such advances would facilitate personalized surveillance based on microbial composition, microbiota-targeted precision medicine, and comprehensive management approaches incorporating dietary and lifestyle interventions.