Evaluation of three new techniques for the detection of STb-positive Escherichia coli strains.

A study was conducted to compare different techniques for the detection of heat-stable enterotoxin b (STb)-positive E. coli strains. Antisera against purified STb was used to develop an enzyme-linked immunosorbent assay (ELISA). STb-positive strains identified by ELISA were tested for bioactivity in rat jejunal loops. Our ELISA was as sensitive as, but less specific than, the bioassay for detection of STb-positive strains. A non-radioactive DNA probe to detect the gene coding for STb was also developed by incorporating digoxigenin-11-dUTP into DNA by the random primed labelling technique. The non-radioactive digoxigenin-labelled DNA probe demonstrated a similar detectability to the radioactive probe and was more convenient to manipulate but was less sensitive and specific than the bioassay and the radioactive probe. In addition, the polymerase chain reaction (PCR) was used to amplify a specific portion of the gene coding for STb. The PCR was a highly specific and practical technique for the detection of STb-positive strains. All E. coli strains tested containing the STb gene produced the STb toxin.