Comparison of five assays for the heat-labile enterotoxin of Escherichia coli

Enzyme-linked immunosorbent assay (ELISA), DNA-DNA hybridisation, Vero cell assay, the Biken test and a new membrane-filter method were compared in the detection of heat-labile enterotoxin (LT) of Escherichia coli. Six subcultures of each of 50 strains of E. coli from the Biken collection were evaluated "blind" in the laboratory. The combined results of the most reproducible tests (ELISA and DNA-DNA hybridisation) were used to calculate the sensitivity and specificity of the other assays. The Vero-cell assay had a high sensitivity (98%) but a lower specificity (91%). The Biken and membrane-filter assays had sensitivities of 58-71% and 77-84% respectively, depending on the type of antiserum used. Only one false positive result was obtained with the Biken test; specificity of the membrane-filter assay was 94-95%. The membrane-filter assay, with anti-cholera toxin, is specific and reasonably sensitive. It has particular advantages over DNA-DNA hybridisation and the Biken test, and it may prove suitable for screening large numbers of E. coli isolates in epidemiological studies in developing countries.