Type 1 fimbriae from two strains of Escherichia coli, K-12-derived CSH50 and a clinical isolate VL-2, were purified by a simplified procedure, which should be applicable to a variety of bacterial strains. After mechanical removal from the cells, the fimbriae were sedimented in the ultracentrifuge and resuspended in 5 M urea to disaggregate cell membranes and flagella, leaving the urea-resistant fimbriae intact. After several hours at 37 degrees C, this crude fimbrial suspension was diluted to 1 M urea, and the intact fimbriae were sedimented through a 1 M urea-1 M sucrose cushion. The pellet was found to be pure fimbriae by sodium docecyl sulfate-polyacrylamide gel electrophoresis, with apparent subunit molecular weights of 17,000 for the fimbriae from K-12 strain CSH50 and 19,000 for those from the clinical isolate VL-2. High-titer rabbit antiserum raised against CSH50 fimbriae was specific for fimbriae by indirect ferritin labeling and immunoprecipitation and was used to develop an enzyme-linked immunosorbent assay. Competitive inhibition of antifimbrial antiserum in the enzyme-linked immunosorbent assay by a known amount of either purified fimbriae or fimbriae-bearing bacteria permitted precise quantitation of fimbrial antigen in cultures of strain CSH50, thereby providing a simple means of determining the effects of environmental conditions on the synthesis of type 1 fimbriae.

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 singe 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.

Previous work on the control of fimbriation in bacteria has demonstrated the importance of environmental factors such as static versus shaking broth and the absence versus the presence of glucose on the degree of fimbriation. When the Pil+ K-12 strain of Escherichia coli CSH50 was grown in static broth, the bacteria grown with glucose were less fimbriate (as determined by electron microscopy) than those grown without glucose. In contrast, a derivative, the pil-lac operon fusion strain VL361, gave off similar proportions of Lac+ and Lac- colonies when grown with or without glucose. Introduction of delta cya into either CSH50 or VL361 did not affect synthesis of either fimbriae or beta-galactosidase, respectively. When total synthesis of fimbriae by strain CSH50 was assayed, using an enzyme-linked immunosorbent inhibition test, glucose-grown bacteria made less antigen when they were grown in static broth but not when they were grown in shaking broth. When results are taken together, we interpret them as showing that glucose does not suppress fimbrial synthesis by classic catabolite repression but rather merely prevents the outgrowth or fimbriate bacteria in static broth.

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The export of fimbrial subunits was found to be diminished at the restrictive temperature in a strain bearing a secA(Ts) mutation. Likewise, export was inhibited in a strain harboring a malE-lacZ protein fusion upon induction of hybrid protein synthesis. Both conditions resulted in the accumulation of a precursor protein ca. 2,000 daltons larger than the mature fimbrial subunit.