Isolation and characterization of a monoclonal antibody directed against type 1 fimbriae organelles from Escherichia coli.

We have isolated a mouse immunoglobulin M (IgM) monoclonal antibody directed against type 1 fimbriae from the Escherichia coli K-12-derived strain CSH50. Antibody specificity was demonstrated by (i) the ability of fimbriate but not nonfimbriate bacteria to compete with solid-phase purified fimbriae for antibody binding in an enzyme-linked immunosorbent assay, (ii) the visualized binding of antibody to fimbriae alone by electron microscopy, and (iii) the appearance in a radioimmunoprecipitation assay of a single electrophoretic band comigrating with pure type 1 fimbriae. The monoclonal antibody was further characterized by immunoblot analysis and compared with previously prepared rabbit anti-fimbrial antisera. Whereas the monospecific but polyvalent antisera recognized both fimbrial monomeric subunits and non-disaggregated fimbriae organelles, the monoclonal antibody recognized only the intact organelles even when the samples were prepared under nondenaturing conditions. The monoclonal antibody, therefore, might be directed against an epitope spanning two (or more) adjacent fimbrial subunits.