Ganglioside GM1 enzyme-linked immunospot assay for simple identification of heat-labile enterotoxin-producing Escherichia coli.

A new method has been developed for demonstration of heat-labile (LT) enterotoxin produced by Escherichia coli. This method is based upon the release of LT from bacteria grown directly onto agar plates which have been coated with ganglioside GM1. Toxin bound to the GM1 solid state is subsequently demonstrated by means of a three-step immunoenzymatic procedure in which enzyme-substrate reactions are visualized as dark spots in agarose. When analyzing LT production from 105 E. coli strains, results obtained by this procedure (GM1-ELISPOT) correlated well with those of the GM1 enzyme-linked immunosorbent assay (GM1-ELISA); in no instance were any false-positive reactions observed when highly specific monoclonal antibodies against LT were used. Easy to perform, the GM1-ELISPOT allows demonstration of LT within 24 h after inoculation of the plates, and large numbers of specimens can be screened at the same time without the need of any special equipment. Thus, this new method should meet the requirements of any diagnostic laboratory.