Background/Aims: Omeprazole, a benzimidazole proton pump inhibitor, has an antibacterial effect against Helicobacter pylori at neutral pH and inhibits its urease activity. The aim of this study was to characterize H. pylori acid resistance and to determine whether omeprazole affects its survival at low pH. Methods: We studied survival of H. pylori and other enteric organisms in buffered solutions (pH 2-7) in the presence or absence of 10 mmol/L urea and/or Omeprazole. Results: In the absence of urea, the acid tolerances of wild-type H. pylori, a urease-negative H. pylori mutant, Escherichia coll, and Proteus mirabilis were similar. In the presence of urea, the survival of the wild-type H. pylori at pH 2 was significantly greater than that of the other organisms. Omeprazole (100 μ/mL) had a marked inhibitory effect on the survival of both wild-type and urease-negative H. pylori at low pH, and similar effects on E. coli, P. mirabilis, and Salmonella typhimurium. Conclusions: Whereas survival of H. pylori below pH 4 is urease dependent, H. pylori uses non-urease-mediated mechanisms at or above pH 4. Omeprazole inhibits the survival of H. pylori at low pH through a mechanism independent of its effect on urease, an antibacterial effect that extends to other enteric bacteria.
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