[Specific detection of the thermolabile enterotoxin of Escherichia coli in human feces by competitive immunoenzyme tests in the presence of protease inhibitors].

Two simple two-step competitive enzyme-linked immunoassays for human E. coli heat-labile enterotoxin (LTh) employing microtitration plates coated with rabbit anti-LTh antibody (ELISA) or GM1 ganglioside (GM1-ELISA) are described. LTh of the test sample competed with the same toxin coupled with horse-radish peroxidase. ELISA and GM1-ELISA were able to detect, respectively, as low as 5 ng and 6.5 ng TLh/ml and up to 9 and 11 micrograms TLh/ml. Both techniques were applied to the study of 167 infant diarrhoeas; ETEC producing LTh were identified in 17 diarrhoeal stools. When the faeces were diluted in phosphate buffer, only 17.6% (3 stools) and 29% (5 stools) of LTh-positive faeces were identified in ELISA and GM1-ELISA. When the stools were diluted with phenylmethylsulphonyl fluoride (PMSF), a synthetic protease inhibitor, 82% (14 stools) and 88% (15 stools) of LTh-positive stool supernatants were detected. Aprotinin, another protease inhibitor, was without effect and foetal calf serum, horse serum and bovine serum albumin enabled detection of only a low percentage of LTh-positive stools.