DNA inoculation with a plasmid vector carrying the faeG adhesin gene of Escherichia coli K88ab induced immune responses in mice and pigs.

pCB01, an eukaryotic expression vector, was constructed by cloning faeG, the gene that encodes the fimbrial adhesin of Escherichia coli K88ab, in pcDNA3. Mice and swine were inoculated by the intramuscular route with different quantities of plasmid DNA to evaluate its capacity to induce an immune response. The immune response was monitored by ELISA and immunoblotting, using purified fimbriae and whole suspensions of fimbriated bacteria. Mice showed seroconversion 21 days after the inoculation of 8.9 microg and swine after the administration of 1100 microg of plasmid DNA. Seroconversions increased after successive reinoculations. Immunoblotting showed that sera collected 73 days after the first inoculation recognized exclusively a protein of 27 kDa present in purified fimbrial suspensions and in whole suspensions of E. coli K88ab. The immune response elicited by pCB01 was mainly due to IgG2a, while that elicited by a bacterin was due to IgG2b and IgG3. Antibodies were still detected 14 months after the initiation of the immunization.