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Sequences regulating production of fimbriae were cloned from two enterotoxigenic Escherichia coli strains. One cloned region, from E. coli 025.H42, controlled expression of coli surface-associated (CS) antigen 4, whereas the function of the other, from E. coli 0167.H5, was unclear. Both regulators were related to the cfaD gene that controls expression of colonization factor antigen I (CFA/I) although low stringency conditions were required to show significant hybridization between cfaD and the regulatory fragment from E. coli 0167. The cloned regulatory genes promoted expression of CFA/I, CS1, CS2 and CS4 antigens but the levels of production in the presence of the 0167 regulator were lower than those promoted by the CS4 regulator of cfaD.

Two enterotoxigenic Escherichia coli strains of serotype 0.25.H42 that produced coli surface associated antigens CS4 and CS6 hybridized with a probe containing the cfaD sequence that regulates expression of colonization factor antigen CFA/I. Transformation of a cloned cfaD gene into some derivatives of the strains that were negative for CS4 and CS6 resulted in expression of CS4 but not CS6. By hybridization the sequence that regulated CS4 production in the wild type 025 strains was located on a plasmid that also encoded the CS6 antigen. The structural genes for the CS4 antigen were on a separate plasmid. The 025 strains carried a third plasmid encoding enterotoxin production which was therefore unlinked to regulation sequences or genes encoding CS antigens.

Enterotoxigenic Escherichia coli (ETEC) with colonisation factor antigens I and II (CFA/I and CFA/II) and PCF8775 were examined in the ‘salting-out’ test to assess the hydrophobicity of the individual adhesion antigens. The fimbrial antigens CFA/I and the coli surface antigens CS1, 2, 4 and 5 were all strongly hydrophobic. The fibrillar fimbrial antigen CS3 was weakly hydrophobic; this antigen is apparently non-fimbrial.

Immunoglobulins, prepared from polyclonal rabbit antisera raised against Escherichia coli fimbrial antigens, colonization factor antigen (CFA)/I, and coli-surface-associated antigens (CS)1, CS2 and CS4, were used to assess antigenic cross-reactions between these four fimbrial types by Western immunoblotting. Antibodies in a serum, prepared against CS4, cross-reacted strongly with the fimbrial subunits of CFA/I, CS1 and CS2. Antibodies in sera prepared against CFA/I and CS1 gave weak reactions with CS1 or CFA/I respectively and also with CS2 and CS4, while the antiserum prepared against CS2 did not react. CS4 antiserum also reacted with the CS17 fimbrial subunit, but not with the subunits of fimbrial antigens: CFA/III, CS5, putative colonization factor (PCF) 0159: H4 or PCF0166.

Sequences encoding the CS6 antigen of colonisation factor antigen (CFA)IV were cloned on a 3kb ClaI fragment. The recombinant plasmid pDEP5 coded for surface expression of CS6 measured by ELISA and production of CS6 polypeptides was detected in E. coli minicells. The genes for the CS1, CS2 and CS3 components of colonisation factor antigen CFA/II were cloned together on a length of DNA corresponding to about 17kb. CS3 was always expressed but production of either CS1 or CS2 depended on the serotype and biotype of the host strain. Separate subclones were obtained that expressed CS3 or CS1 and CS2.

The CS2 fimbrial antigen was isolated by salt and isoelectric precipitation and by column chromatography. The purified antigen was free of other fimbrial proteins present on the same bacterial strain. Analysis of the N-terminal amino acid sequence indicated extensive homology with the CFA1 fimbrial antigen, which was surprising since the two proteins do not show any immunological cross reactivity. It could therefore be concluded that the N-terminal parts of these fimbrial proteins are not located on the surfaces of the proteins and might be involved in conservation of the structural integrity of these proteins.