Development of a blocking enzyme-linked immunosorbent assay for detection of serum antibodies to O157 antigen of Escherichia coli.

The O157 antigen of Escherichia coli shares structural elements with lipopolysaccharide (LPS) antigens of other bacterial species, notably Brucella abortus and Yersinia enterocolitica 09, a fact that confounds the interpretation of assays for anti-O157 antibodies. To address this problem, a blocking enzyme-linked immunosorbent assay (bELISA) was designed with E. coli O157:H7 LPS as the antigen and a monoclonal antibody specific for E. coli O157, designated 13B3, as the competing antibody. The bELISA had equivalent sensitivity to, and significantly higher specificity than, the indirect ELISA (iELISA), detecting anti-O157 antibodies in sera from cattle experimentally inoculated with O157:H7. Only 13% of sera from naive heifers vaccinated for or experimentally infected with B. abortus had increased anti-O157 bELISA titers, while 61% of anti-O157 iELISA titers were increased. The bELISA is a sensitive and specific method for the detection of serum antibodies resulting from exposure to E. coli O157.