Effects of Helicobacter pylori and Nitrate-Reducing Bacteria Coculture on Cells.

infection is an important risk factor for developing gastric cancer. However, only a few -infected people develop gastric cancer. Thus, other risk factors aside from infection may be involved in gastric cancer development. This study aimed to investigate whether the nitrate-reducing bacteria isolated from patients with atrophic gastritis caused by infection are risk factors for developing atrophic gastritis and gastric neoplasia. Nitrate-reducing bacteria were isolated from patients with atrophic gastritis caused by infection. Among the isolated bacteria, , , , and were used in the subsequent experiments. Cytokine inducibility was evaluated in monocytic cells, and mitogen-activated protein kinase (MAPK) activity and cell cycle were assessed in the gastric epithelial cells. The cytotoxicities and neutrophil-inducing abilities of the and species were enhanced when cocultured with . Th1/Th2-related cytokines were also expressed, but their expression levels differed depending on the bacterial species. Moreover, and activated MAPK (ERK and p38) and affected cell cycle progression. Some nitrate-reducing bacteria cocultured with may promote inflammation and atrophy by inducing cytokine production. In addition, the MAPK activation and cell cycle progression caused by these bacteria can contribute to gastric cancer development.