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目的：许多研究证实，萎缩性胃炎患者胃内细菌繁殖增多与Ｎ－亚硝酰胺含量升高有关。因此该实验模拟胃低酸情况下，胃内细菌催化Ｎ－亚硝酰胺合成情况及合成量为研究宗旨。方法：采用患者空腹胃液中经培养、分离、鉴定的１３种４６株细菌，以甲基脲（ＭＵ）及亚硝酸纳（ＮａＮＯ２）为底物加入活菌悬液在近中性条件下进行Ｎ－甲基－Ｎ－亚硝基脲（ＭＮＵ）催化合成反应，用ＨＰＬＣ－ＰＨＰＳ－ＴＥＡ法定量测定。结果：（ａ）ｐＨ分别为５，６，７时，１３株细菌催化ＭＮＵ合成能力以ｐＨ６时最高，占９２３％。（ｂ）ｐＨ６时，４６株细菌催化ＭＮＵ合成能力不同；经筛选阳性菌６株，其中金黄色葡萄球菌合成量最高。（ｃ）多株菌混合液催化实验，催化能力与混合菌中阳性菌个体所占比例有关，比例高合成能力强；阳性菌与阴性菌相混合不影响其催化合成能力。结论：胃内细菌具有催化强致癌物Ｎ－亚硝酰胺合成的能力，其合成量决定于胃液ｐＨ、阳性菌株浓度、前体物浓度等因素
OBJECTIVE: Many studies confirm that the increase in bacterial reproduction in the stomach of patients with atrophic gastritis is associated with increased N-nitrosamide content. Therefore, this experiment simulates the situation of gastric hypotonic acid, and the intragastric bacteria catalyze the synthesis of N-nitrosamide and the amount of synthesis as the research objective. METHODS: Thirty-six strains of 46 strains were cultured, isolated and identified in the fasting gastric juice. Methylurea (MU) and sodium nitrite (NaNO2) were added as the substrate to the suspension of viable bacteria. N was performed under near-neutral conditions. The reaction was catalyzed by methyl-N-nitrosourea (MNU) and quantified by HPLC-PHPS-TEA. Results: (a) When pH was 5, 6, and 7, 13 strains of bacteria catalyzed the synthesis of MNU at the pH of 6 and the highest was 92. 3%. (b) At pH 6, 46 strains of bacteria catalyzed the synthesis of MNU with different capacities; 6 strains of positive bacteria were screened, of which the synthesis of Staphylococcus aureus was the highest. (c) Catalyzed by a mixture of multiple strains of bacteria, the catalytic ability is related to the proportion of positive bacteria in the mixed bacteria, and the ratio is high; the ability to synthesize is strong; the combination of positive bacteria and negative bacteria does not affect their catalytic synthesis ability. Conclusion: Gastrointestinal bacteria have the ability to catalyze the synthesis of strong carcinogen N-nitrosamide. The amount of synthesis depends on the pH of gastric juice, the concentration of positive strains and the concentration of precursors.