The Role of Nitrate-Reducing Bacteria Isolated from Helicobacter pylori-Infected Individuals in Gastric Cancer Development

Helicobacter pylori is a Gram-negative bacterium that inhabits the gastric mucosa, with a global prevalence in humans of approximately 40%. It is likely the cause of 90% of gastric cancer (GC) cases and thus considered the most prominent driver of GC development. However, during gastric mucosal atrophy, other bacteria such as nitrate-reducing bacteria (NRB) also proliferate. In this study, we isolated NRB from patients with gastritis and GC to examine their effects on the epithelial cell cycle and production of various cytokines in monocytic cell lines. Bacterial counts (excluding H. pylori and NRB) increased with the progression of gastric mucosal atrophy and were significantly higher in patients with GC. Gastric epithelial cell lines were stimulated with isolated NRB, and the proportion of cells in each cell cycle was measured. Strains from patients with open-type gastritis progressed more rapidly through cell cycles than those from patients with GC. NRB isolated from gastric cancer had high nitrate-reducing activity. Thus, NRB may contribute to GC progression during H. pylori-induced carcinogenesis. Therefore, evaluating gastric atrophy and microbiota may be important for managing the risk of GC.