Bacteria which produce putrefaction and gas in the intestines cannot live in lactic acid.

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So by building up the concentration of ammonium ions inside its retaining membrane, H. pylori is able to fend off the destructive attentions of the hydrogen ions in stomach acid and thus live free from competition by less hardy germs.

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On Earth there are micro-organisms that can live, and even thrive, in acidic water, even battery acid.

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