Reciprocal exchange of minor components of type 1 and F1C fimbriae results in hybrid organelles with changed receptor specificities.

Type 1 and F1C fimbriae are surface organelles of Escherichia coli which mediate receptor-specific binding to different host surfaces. Such fimbriae are found on strains associated with urinary tract infections. The specific receptor binding of the fimbriae is due to the presence of receptor recognition proteins present in the organelles as minor structural elements. The organization of the fim and foc gene clusters encoding these fimbriae, as well as the structures of the organelles, are very similar, although the actual sequence homology of the structural elements is not remarkable; notably, the sequence identity between the minor components of the type 1 and F1C fimbriae is only 34 to 41%. Type 1 fimbriae mediate agglutination of guinea pig erythrocytes, whereas F1C fimbriae do not confer agglutination of any types of erythrocytes tested. However, F1C fimbriae mediate specific adhesion to epithelial cells in the collecting ducts of the human kidney as well as to cells of various cell lines. This report addresses the question of fimbrial promiscuity. Our data indicate that minor fimbrial structural elements can be exchanged between the two fimbrial systems, resulting in hybrid organelles with changed receptor specificity. This is the first study on reciprocal exchange of structural components from two different fimbrial systems.