H. pylori · the one cause of cancer you can cure

幽门螺杆菌 · 唯一能被根除的癌症病因

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它没碰到胃酸, 靠尿素酶造碱性云 · Correa 级联走几十年 · CagA 像针管扎进细胞 · 沿着饭桌传播, 该改的是公筷不是人 · 根除降风险但不归零

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Digestive
H. pylori does not survive in stomach acid; it burrows under the mucus layer and sits on the epithelial surface, where the pH is near neutral — the one mild spot in the stomach. Understanding that move requires knowing how the acid is made and how the mucus barrier works.

How it survives the acid

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它怎么在胃酸里活下来

Stomach acid kills nearly every bacterium you swallow with food. One survives — not because it withstands the acid, but because it never touches the acid.

It's *Helicobacter pylori* (H. pylori). It carries one piece of equipment: urease, an enzyme that splits urea. Gastric juice already contains a little urea, and urease splits it into ammonia and carbon dioxide. Ammonia is alkaline, and it neutralizes the acid seeping in around the bacterium on the spot — a cloud of alkali wrapped around itself (Scott 2002).

The device even has a power-saving switch. A small gate on the bacterial surface lets only urea through. It normally stays shut and opens only as acid closes in — no effort wasted when there's no acid.

But it still has to leave the strong acid of the stomach cavity. A layer of mucus covers the stomach wall, thick as gel. It was long assumed the corkscrew body screwed its way in, but the real mechanism is neater: urease raises the pH nearby, the mucus turns from gel to fluid, and the bacterium swims through on its flagella (Celli 2009).

Under the mucus, it settles on the surface of the stomach's own cells. The pH there is near neutral — the only mild spot in the stomach. So it doesn't live *in* the acid; it lives underneath it. For how stomach acid is made and how the mucus barrier works, see the digestive system island.

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Educational content, not medical advice — consult a clinician.

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