The use of the Biken test to detect enterotoxigenic "Escherichia coli" producing heat labile enterotoxin.

For identification of enterotoxigenic Escherichia coli producing heat labile enterotoxin (LT), various assay methods have been developed. However, many of these assay methods are unsuitable for routine clinical purposes, especially in developing countries, because they need special materials or techniques or both, such as a large number of animals, stocks of special tissue culture cells, and radioisotopes. Recently, we developed a simple and reproducible assay method, Biken test, which can be widely used in clinical laboratories in both developing and developed countries (15). This method is based on the principles of the Elek test and Ouchterlony double gel diffusion test. The Biken test was used in a field study in Bangladesh with good results (14). Moreover, the Diarrheal Diseases Control Programme, WHO, organized a multi-laboratory study to evaluate the accuracy and reproducibility of the Biken test, in which 5 investigators tested an identical set of 100 unknown strains of E. coli, using the Biken test and at least one other assay method, which includes CHO cell assay, Y1 adrenal cell assay, GM1 ganglioside ELISA, DNA probe test and passive immune hemolysis. The results reported by Sutton (International Symposium on Bacterial Diarrheal Diseases, Osaka, 1982) showed that the Biken test was a reliable assay method. To evaluate further the Biken test, we tested a total of 2,229 strains of E. coli isolated from diarrheal patients. The results showed 99.0% coincidence with those obtained by CHO cell assay. The use of anti-LT antiserum gave sharper and clearer results than cholera antitoxin. Samples for heat stable enterotoxin (ST) assay were obtained from the agar plates used for the Biken test and the ST activities of these samples were compared with those of samples obtained from standard liquid cultures. Results on samples of 2,229 strains from the Biken agar plates and from liquid cultures were almost identical.