Induction of colonization factor antigen I (CFA/I) and coli surface antigen 4 (CS4) of enterotoxigenic Escherichia coli: relevance for vaccine production.

Regulatory proteins control the expression of the fimbrial colonization factor antigens CFA/I and CS4 of enterotoxigenic Escherichia coli (ETEC). To examine the mechanism behind lack of expression of these antigens in spontaneous CFA-negative mutants, we mobilized a recombinant plasmid harbouring the cfaD gene, which encodes a positive regulator of CFA/I and CS4 expression, into such derivatives. In electron microscopy, the induced surface structures were morphologically identical to the fimbriae of the CFA/I+ and CS4+ wild type strains. Immunogold labelling with monoclonal antibodies showed that the distribution of CFA/I and CS4 specific epitopes along the induced fimbriae was indistinguishable from that of the wild type strains. The percentage of fimbriated cells was consistently higher in the cfaD transformants than in the corresponding wild type strains. The present work reports on the efficiency of the cloned cfaD gene in restoring and enhancing the production of morphologically intact CFA/I and CS4 fimbriae.