An enzyme-linked immunosorbent assay-based isolation procedure for verotoxigenic Escherichia coli

A colony enzyme-linked immunosorbent assay using the hydrophobic grid membrane filter format was developed for the isolation of verotoxigenic Escherichia coli from human and food samples. The method utilizes monoclonal antibodies directed against the verotoxins and is sensitive to all verotoxin 1- and/or 2-producing serotypes. E. coli that produced a minimum of 2 x 10(2) and 2 x 10(3) 50% cytotoxic doses per ml of verotoxins 1 and 2, respectively, were detectable. In a method comparison using human stool specimens, this procedure isolated 29% more E. coli O157 than did the standard sorbitol-MacConkey agar procedure, with no false-positive reactions. When applied to meat, 11 of 20 samples positive for verotoxin by polymyxin extraction yielded verotoxigenic E. coli of a variety of serotypes including O157:H7. Four false positives were noted. This procedure provides a sensitive means for the isolation of verotoxigenic E. coli and should facilitate recovery of those serotypes that are otherwise indistinguishable from nonpathogenic strains.