Linear epitopes of colonization factor antigen I and peptide vaccine approach to enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) cause diarrhea in infants and in travelers to developing countries. The bacteria utilize colonization factors (CF) for adherence to intestinal epithelia, then release toxins causing diarrhea. CF are strong immunogens as well as protective antigens. While 20 ETEC CF have been described in the literature, 11 CF are prominent enough to be considered for vaccine targeting. Of this group, six of the members fall into the CFA/I family of CF. Geysen pin (peptide) linear epitope analysis demonstrated that three regions containing linear epitopes exist in CFA/I, and that both B- and T-cell linear epitopes of CFA/I were concentrated at the N-terminus of the protein. We have determined N-terminal sequence of the CFA/I family members not previously sequenced. Comparison of the protein sequence of the six members of the family showed a strong homology up to residue 36. A peptide of 36 amino acids representing a consensus of the six sequences was synthesized and used to immunize animals. The antibody induced to the peptide was reactive to the peptide as well as cross-reactive to each member of the CFA/I family in Western blots. In addition, this antibody agglutinated three of the six members of the CFA/I family when added to whole cells expressing the native CF. We are currently evaluating different carriers and conjugation methods to maximize production of high titer, agglutinating antibody. It is hoped that this and related research will result in an effective and inexpensive cross-reactive and cross-protective ETEC vaccine.