Simple and reliable enzyme-linked immunosorbent assay with monoclonal antibodies for detection of Escherichia coli heat-stable enterotoxins

Abstract

We have developed a sensitive and specific competitive enzyme-linked immunosorbent assay for Escherichia coli heat-stable enterotoxins consisting of methanol-soluble, suckling mouse active peptides with similar core sequences (ST(a)) by using monoclonal antibodies prepared against ST(a) purified from a human isolate. The assay can detect 3 to 20 pg of purified ST(a), depending on the monoclonal antibody used in the assay. The assay is rapid, requiring ca. 1 h to complete. With this competitive enzyme-linked immunosorbent assay, we measured ST(a) production by enterotoxigenic E. coli directly in Casamino Acid-yeast extract culture supernatants. The assay was suitable for measuring ST(a) in culture supernatants from human, bovine, and porcine E. coli isolates. No cross-reactivity was observed with heat-labile enterotoxin, cholera toxin, or heat-stable enterotoxin ST(b), which is a methanol-insoluble peptide(s) active in the ligated pig jejunal loop test. A 100% correlation of toxin production was found by comparing the enzyme-linked immunosorbent assay with the previously established radioimmunoassay for ST(a) and with suckling mouse activity.