Like sailors who lash their boats to a dock with mooring lines, bacteria attach themselves to cells with threadlike extensions called pili. At the tip of each pilus is an adhesin, a protein designed to stick to a surface molecule of the bacterium's target cells.
Scientists have now identified an adhesin used by Escherichia coli, the bacteria that cause the great majority of bladder infections in women. Furthermore, experiments using mice and human bladder cells suggest that the newly discovered adhesin may serve as an effective vaccine against such infections, which generate an estimated $1 billion in medical costs annually in the United States alone.
The new adhesin, known as FimH, was discovered by a research group headed by Scott J. Hultgren of Washington University in St. Louis.
A single bacterial cell can make more than one type of pilus, notes Hultgren. E. coli can make both a version known as P pili, which allows it to colonize kidney cells, and one called type 1 pili, which helps it attach to the bladder.
Vaccines consisting of whole pili have been tested in the past, with little success. The vaccines protected against only a few E. coli strains, since the nonadhesin components of type 1 pili vary significantly among strains and the vaccines generate a poor antibody response to FimH. "The adhesin, in the context of the pili, does not provoke a strong immune response," says Hultgren.
His group decided to make a vaccine out of FimH alone, which varies little among E. coli displaying type 1 pili. With their colleagues at MedImmune, a biotech firm in Gaithersburg, Md., the Washington …