A recombinant hybrid peptide composed of AAF adhesin of enteroaggregative Escherichia coli and Shiga toxin B subunit elicits protective immune response in mice.

Shiga toxin producing Escherichia coli (STEC) are a group of diarrheagenic Escherichia coli (E. coli) whereby Shiga toxin is the main virulence factor. It is composed of an A subunit, which mediates toxicity, and a B subunit (StxB), which is a nontoxic homopentameric protein responsible for toxin binding and internalization into target cells by interacting with the glycolipid, globotriaosylceramide (Gb3). Enteroaggregative Escherichia coli (EAEC) are a group of E. coli with aggregative adherence to epithelial cells, which play an important role in its pathogenesis. EAEC are the cause of diarrhea in developing countries and in the developed world. Aggregative adherence fimbria (AAF) of EAEC represents the adhesin that confers the presence of aggregative adherence (AA) phenotype on EAEC strains. The gene encoding non-toxic B subunit of Shiga toxin (StxB) was coupled to aggregative adherence fimbriae (AAF) of the EAEC structural gene. The resulting polypeptides (B-AAF/I, B-AAF/II) were designed to elicit immune response in immunized mice with recombinant peptides. The antibody, hence obtained, inhibited the adherence of prototype EAEC strains to HeLa cells and, on the other hand, protected the immunized mice against a lethal dose of Shiga toxin. Therefore, this promising data could indicate that this kind of polypeptide strategy is a good candidate for any probable vaccine design against diarrheal infection.