PLoS Pathog. 5, e1000407 (2009)

The bacterium associated with stomach ulcers creates a habitable environment by clinging to human cells and interfering with their polarity.

Helicobacter pylori avoids the stomach's lethal acidity by colonizing a thin layer of mucus that coats stomach epithelial cells. These cells are polarized — that is, the outside surface facing the stomach and the inside surface, which backs onto the underlying tissue, have different properties.

Manuel Amieva and his colleagues at Stanford University in California found that the bacterium can thrive when attached to these cells in culture, even when the culture medium lacks nutrients normally required for survival. However, H. pylori mutants that lacked a protein called CagA were not able to colonize the outside surface of these cells. CagA is known to alter the polarity of epithelial cells, presumably making the outside surface of the cells more like the inside surface, and thus making them colonizable.