Detection of heat-labile-enterotoxin-producing colonies of Escherichia coli and Vibrio cholerae by solid-phase sandwich radioimmunoassays.

A solid-phase sandwich assay that was able to differentiate heat-labile-enterotoxin-producing colonies of Escherichia coli and choleratoxin-producing colonies of Vibrio cholerae from nontoxigenic colonies is described. Flexible polyvinyl chloride plastic film coated with antibody molecules was allowed to react with partially lysed bacterial colonies in a standard petri dish. The immobilized antigen on the plastic film was then labeled with radioiodinated antibody. Autoradiography identified antigen-containing colonies. As little as 5 to 25 pg of pure toxin contained in a 3- to 4-mm-diameter circle was reliably detected by this method. The synthesis of heat-labile enterotoxin and choleratoxin by cells growing on selective media such as eosin methylene blue agar, MacConkey agar, Endo agar, and thiosulfate-citrate-bile salts-sucrose agar was demonstrated. The method appears to be suitable for large-scale surveys.