Abstract
Helicobacter pylori colonized the highly acidic human gastric mucosa. At pH 3.0 to 7.0, this bacterium maintained a nearly neutral internal pH. Its membrane potential changed reciprocally with the pH gradient so that a relatively constant proton motive force was maintained. Possible, the capacity to maintain an appropriate transmembrane ionic gradient at a low pH contributes to the pathogenic propensities of this bacterium.