Marshall B J, Barrett L J, Prakash C, McCallum R W, Guerrant R L
Department of Medicine, University of Virginia, Charlottesville.
Gastroenterology. 1990 Sep;99(3):697-702. doi: 10.1016/0016-5085(90)90957-3.
Colonization of the stomach with Helicobacter (Campylobacter) pylori is common in patients with duodenal ulcer disease, which is known for its high acid secretion. Although the bacterium is usually isolated by culture of a gastric biopsy specimen, viable organisms may sometimes be found in the acidic gastric juice. It was postulated that urease, by generating ammonia, protected H. pylori from acid. To test this hypothesis, the pH susceptibility of H. pylori, Proteus mirabilis, and the urease-negative Campylobacter jejuni was examined in the presence and absence of urea. It was found that without urea the three bacteria were all highly susceptible to acid. In striking contrast, the addition of 5 mmol/L of urea completely protected H. pylori but not P. mirabilis or C. jejuni from pH values as low as 1.5. Furthermore, the protective effect of urea on H. pylori was found with urea concentrations as low as 0.05 mmol/L. It is concluded that the high urease activity of H. pylori enables it to survive in gastric acid.
十二指肠溃疡病患者中幽门螺杆菌（弯曲杆菌属）在胃内定植很常见，十二指肠溃疡病以胃酸分泌过多为特征。虽然该细菌通常通过胃活检标本培养分离得到，但有时在酸性胃液中也可发现活的细菌。据推测，脲酶通过产生氨来保护幽门螺杆菌免受酸的侵害。为了验证这一假设，研究了在有和没有尿素存在的情况下幽门螺杆菌、奇异变形杆菌和脲酶阴性的空肠弯曲菌对pH的敏感性。结果发现，在没有尿素的情况下，这三种细菌都对酸高度敏感。与之形成鲜明对比的是，添加5 mmol/L的尿素可使幽门螺杆菌完全免受低至pH 1.5的酸性环境影响，而奇异变形杆菌和空肠弯曲菌则不能。此外，发现尿素浓度低至0.05 mmol/L时对幽门螺杆菌也有保护作用。结论是幽门螺杆菌的高脲酶活性使其能够在胃酸中存活。
