Construction of a hybrid plasmid coding for adherence antigen K88AB as well as the B subunit of Escherichia coli thermo-labile enterotoxin and mouse immune response to the encoded antigens

A hybrid plasmid (pUB 3744) encoding the adherence antigen K88ab and the B subunit of Escherichia coli heat-labile enterotoxin (LT-B) was prepared by linking plasmids pFM 205 (K88ab(+)) and pUB 1844 (LT-B+). The three plasmids were subsequently transferred to the porcine E, coli strain 045:K, producing variants K88ab(+), LT-B+ and K88ab(+)/LT-B+. These variants were orally given to distinct groups of mice on five consecutive days. The isotype-specific antibody response to K88ab, LT-B and to sonicated bacterial antigen was measured after a further five days in serum and scrapings of intestinal mucosa. Excretion of the inoculated bacteria was monitored by culturing fecal samples. Strain LT-B+ persisted longer in the intestine and induced a local immune response to LT-B (IgA, IgG and IgM). No antibody to K88ab was found in mice inoculated with the strain producing only K88ab, but mice inoculated with strain K88ab(+)/LT-B+ showed an increase in intestinal antibody levels to K88ab. All mice inoculated with the 045:K- variants had an increase in serum IgA levels to sonicated bacterial antigens, which were higher in animals fed with variant K88ab(+)/LT-B+.