Development and evaluation of an ELISA to detect Escherichia coli K88 (F4) fimbrial antibody levels.

An enzyme-linked immunosorbent assay (ELISA) to determine IgG antibody levels against K88 (F4) fimbrial antigen from porcine enterotoxigenic Escherichia coli (ETEC) has been developed. The ELISA method was checked with serum samples obtained from rabbits and pigs, and the parameters affecting the method were also analysed. ELISA plates were optimally coated with K88 antigen 0.5 microgram/ml for testing rabbit antiserum or with 1.25 microgram/ml for testing pig serum. Optimal concentrations of H202 (0.5%) and orthophenylene-diamine (OPD) (0.125%) were chosen when a 10-min incubation period was used. The expression of antibody levels as enzyme-immunosorbent units (EIU) significantly decreased the variability of results between duplicate plates, when compared with the expression of results as direct OD values. ELISA-K88 applied to a field study with serum samples from 141 vaccinated and 52 unvaccinated sows was shown to be useful in differentiating between samples from vaccinated and unvaccinated animals.