Refolded recombinant FaeG adhesin induces a systemic and mucosal F4-specific immune response following oral...

The importance of adhesins in the pathogenicity of several bacteria resulted in studies on their usefulness in vaccines. In this study, the gene of the F4-fimbrial adhesin FaeG of the pathogenic enterotoxigenic Escherichia coli (ETEC) strain GIS26 was cloned into the pET30Ek-LIC vector and expressed with an N-terminal His- and S-tag in the cytoplasm of BL21(DE3). Recombinant FaeG (rFaeG) subunits were isolated from insoluble cytoplasmic aggregates and refolded into a native-like F4R-binding conformation. Indeed, ELISA showed the presence of conformational epitopes and the ability to bind to the F4 receptor (F4R) was observed by inhibiting the adhesion of F4+ ETEC to F4R+ villi with increasing concentrations of native-like refolded rFaeG subunits. The rFaeG subunits appear as monomers, whereas purified F4 fimbriae are multimers. Oral immunization of newly weaned piglets with native-like rFaeG induced a mucosal and systemic F4-specific immune response, significantly reducing F4+ E. coli excretion from 2 till 5 days following challenge infection. However, improvement of stability and immunogenicity of rFaeG must be considered since a higher F4-specific response was obtained following immunization with purified F4 fimbriae. Furthermore, the N-terminal fusion of a His- and S-tag was not detrimental for F4R binding, supporting the use of FaeG as mucosal carrier. In conclusion, this is the first report of an oral immunization with a recombinant fimbrial adhesin subunit of Escherichia coli inducing a mucosal and systemic fimbriae-specific immune response in pigs.