The most acid sensitive, Vibrio cholerae, requires
the highest oral infectious dose, while only a few E. coli
and Shigella must be ingested to cause disease. The
enteric pathogens can protect themselves from acid in
several basic ways. They can prevent protons from entering
the cell, pump protons out of the cell, or, once internal
pH enters a dangerous acid zone, they could protect or
repair damage to macromolecules. Finally, they could
synthesize isoforms of key enzymes with pH optima in
the acid range so they can function when internal pH falls.
Our laboratory has examined the basic systems of acid
tolerance in Salmonella that protect the cell down to pH
3 and the even more effective systems of acid resistance
in E. coli that build on acid tolerance but that protect cells
to pH 2 or less