ESCHERICHIA-COLI HEAT-STABLE ENTEROTOXIN (STA)-BIOTIN ENZYME-LINKED-IMMUNOSORBENT-ASSAY (STA-BIOTIN ELISA)

We have previously shown that an Escherichia coli heat-stable enteroto xin (STa)-biotin conjugate binds to polystyrene microtitre plates coat ed with avidin (Germani et al., 1992). In the present study the STa-bi otin ELISA, based on inhibition of binding of anti-STa antibodies to a vidin-bound STa-biotin conjugates, was compared with the conventional suckling mouse assay for the identification of STa from Biken agar ext racts and from culture supernatants, using 150 E. coli isolates (50 ST a-positive and 100 ST-negative). Pieces of Biken agar were a good sour ce of toxin, 142 of 150 strains gave consistent results by both tests: 100 were negative and 42 were positive; seven of the remaining eight E. coli gave questionable but positive results in the STa-biotin ELISA and were positive by the suckling mouse test; the last E. coli gave n egative result by both tests. The STa-biotin ELISA was 85.7% sensitive and 100% specific; the negative predictive value was 0.935 and the po sitive predictive value was 1. All the 150 strains tested for STa prod uction from standard liquid cultures gave consistent results by both t echniques. The STa-biotin ELISA detected 20 pg of partly purified STa compared to 15 pg in the suckling mouse assay.