The disease occurs when listeria from contaminated food moves from the stomach into the bloodstream, then into the central nervous system. Until now, the molecular events that allow the invasion have been a mystery. The French researchers identified a protein they call internalin on the listeria surface membrane as the key. And they identified the lock as a specific variant of a receptor protein called E cadherin on the surface of intestinal cells. By checking each amino acid in the chain that makes up the receptor molecule, the researchers found that the receptor will react with internalin only if an amino acid called proline is in the 16th position.
Humans have proline in that position.
Mice and rats have a different amino acid, glutamic acid, which does not interact with internalin and therefore prevents listeria infection. The transgenic mice created by the French researchers contain the human form of E cadherin and will be a great help in related research, Finlay says. This gives us an animal model that enables us to look at orally acquired infections. While similar animal models have been developed for viral disease research, this is the first one for a bacterial infection, and it opens the way for similar models for other bacterial infections, including gonorrhea and typhoid fever, Finlay says. What To Do While the research unlocks a secret about bacterial infections, prevention still is the first line of defense.