Use of chicken egg-yolk antibodies against K88+ fimbrial antigen for quantitative analysis of enterotoxigenic Escherichia coli (ETEC) K88+ by a sandwich ELISA

An enzyme-linked immunosorbent sandwich assay (ELISA) has been developed to detect and quantify both the K88+ fimbrial antigen and the concentration of bacterial cells in fecal and other samples using anti-fimbrial chicken egg-yolk and anti-fimbrial rabbit serum antibodies. The assay has a sensitivity of 40ngml^-1 for K88+ fimbrial antigen and 10⁷ CFUml^-1 for intact cells and cell homogenate. The inter- and intra-assay coefficients of variation (CV) for intact cells, homogenates, and fimbrial antigens were similar, suggesting that reproducible results can be obtained with any of the three preparations. In all cases the CV increased with decreasing concentration of the antigen, especially when very low concentrations of antigen were used. Fimbrial antigens had lower CV (values ranged from 2 to 37%, depending on its concentration) than standards prepared from either whole cells or homogenized cells (values ranged from 1 to 67%). The correlation between the actual number of cells as counted and the number as estimated from the ELISA using the amount of fimbrial antigen was r=0.98, P < 0.001. The anti-K88+ polyclonal antibodies from chicken serum and egg yolk had little or no cross-reactivity with K99, 987P ETEC. The correlation (r) between the fecal score for diarrhea and the number of E coli in the fecal swab was high, r = 0.80 (n = 64, P < 0.0001). The assay is sensitive and specific and provides a good estimate of the amount of fimbrial protein or the number of K88+ ETEC in the sample.