Research in the News: Study explains why typhoid toxin targets only humans

The bacterium that causes typhoid fever sickens about 21 million people annually but not other mammals. Researchers at Yale and the University of California-San Diego have discovered an explanation: differences in a single oxygen atom in the human receptor for typhoid toxin.

The bacterium Salmonella typhi causes little harm in other mammals, although in chimpanzees, our closest genetic relative, it can replicate just like it does in humans. The typhoid toxin produced by S. typhi, which is responsible for the disease symptoms in humans, does not sicken chimpanzees or other animals.

In the Dec. 4 issue of the journal Cell, the researchers report that the difference between human and other animals is within a single enzyme that modifies the toxin receptor on the surface of cells.

“The discovery that a single oxygen atom could make such a difference in toxin binding is remarkable and has implications for the design of potential toxin inhibitors,” said Jorge Galan, professor of microbiology and of cell biology and co-senior author of the research.