Monoclonal antibodies to K88ac and K88ab were used in enzyme-linked immunosorbent assays on Escherichia coli cultures known to produce K88 pili. A total of 415 K88-positive E. coli isolates from nine states were all found to be the K88ac variant. The cultures tested were isolated during the years 1976 to 1985.

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Monoclonal antibodies directed against the a determinant of K88 pili from porcine enterotoxigenic Escherichia coli which react with all three K88 variants have been produced. These antibodies have been used for diagnosis of porcine enterotoxigenic E. coli in a direct enzyme-linked immunosorbent assay with sensitivity to 50 ng of pilus protein per ml. Both pilus adhesins and enterotoxins of enteropathogenic Escherichia coli are involved in pathogenesis of noninvasive diarrheal disease (6). The K88 pilus protein antigen (19, 20) is associated with swine infections (1, 14) and has at least three antigenic variants, ab (14, 15), ac (15, 16), and ad (7), of which ac and ad currently predominate (7, 25). The detection of the K88 antigen in porcine E. coli is indicative of the enteropathogenicity of the strain, because K88-positive strains are nearly always also enterotoxigenic (18). The usual methods of detecting E. coli with the K88type pili have been seroagglutinations (3, 4, 26), immunofluorescence (2, 4), or enzyme-linked immunosorbent assay (ELISA) (10, 12) using polyclonal antibodies. Monoclonal antibodies (MAb) have the advantages of increased sensitivity and specificity, while being available in an unlimited supply. The objectives of these experiments were (i) to produce and characterize MAb specific for the a determinant of K88 pili which react with all three K88 variants (ab, ac, and ad) and (ii) to use these antibodies in an ELISA for the detection of K88-positive E. coli isolated from swine.

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