Polyclonal sandwich ELISAs to detect F18 fimbriated Escherichia coli in pigs in Northern Ireland

F18 fimbriated Escherichia coli are a newly described cause of postweaning diarrhea in pigs. Polyclonal rabbit antisera were raised to the antigenic v ariants, F18ab and F18ac, of these fimbriae and were used to develop monosp ecific sandwich enzyme-linked immunosorbent assays (ELISAs). The ELISAs wer e standardized with type cultures characterized by polymerase chain reactio n techniques (PCR) and then used to conduct a study of the prevalence of F1 8 fimbriated E. coli in pigs in Northern Ireland. A total of 176 isolates w ere tested by ELISA and PCR. Eight isolates were positive for F18 by ELISA, of which 2 were shown to be false positives by PCR and one was PCR positiv e but ELISA negative. Of the 6 confirmed ELISA positives, all produced VT2 toxin and 3 produced ST toxin. Four positives were from serogroups O138 and O139, previously associated with porcine diarrhea.