Gerald Pier, of Harvard Medical School in Boston and his colleagues studied the relationship between salmonella typhi, the bacterium that causes typhoid fever, and the protein which, when faulty, causes cystic fibrosis. They showed that S.typhi uses the healthy version of this protein as an entry point into the gut cells that it infects. They also showed that cells which produce a mixture of healthy and unhealthy CFTR(cystic fibrosis transmembrane conductance regulator) are much less likely to become infected.