Colon luminal environment

At pH 4 most bacteria are killed within 30 min, and at physiological luminal pH, 99% of bacteria are killed within 5 min [14], Certain bacteria, like lactobacilli, are more acid-resistant, and some microbes survive the hostile gastric environment by colonizing luminal niches at the mucosal surface, protected by gastric bicarbonate secretion. This is the case for Helicobacter pylori, related spiral-... 

Because of fermentation processes, the luminal environment of the colon is slightly acidic at a pH value around 6.6 [2], Similar pH values can be found in the upper small intestine (pH 6.5 and pH 6.7, in the duodenum and jejunum, respectively), whereas in the ileum the pH is slightly higher at a neutral to alkaline pH value around 7.1 [2], Therefore, the slightly acidic solutions, which are generally used for maintaining physiologically relevant luminal conditions... 

In another study of stress ulcer prophylaxis, 53 critically ill patients were randomized to receive sucralfate 1 g 6-hourly, cimetidine 300 mg 8-hourly, or cimetidine 900 mg/day by continuous intravenous infusion (14). Although bacterial colonization was increasingly likely in patients with a persistent alkaline gastric environment, gastric luminal pH and the degree of bacterial colonization of the stomach were similar in the three groups. 

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