Evaluation of a competitive enzyme-linked immunosorbent assay for porcine Escherichia coli heat-stable enterotoxin.

A competitive enzyme-linked immunosorbent assay (ELISA) was compared with the conventional suckling mouse assay for the identification of heat-stable enterotoxin (STa) in samples from piglets suffering from diarrhea. A total of 110 Escherichia coli isolates, 22 primary cultures, and 26 fecal samples from piglets up to 8 weeks of age with diarrhea were compared in parallel by both assays. Of the 110 isolates tested, all gave consistent results by the ELISA and the suckling mouse assay; 60 strains were negative and 50 strains produced STa by both tests. Identical results were obtained when 22 primary agar cultures were screened for STa production by both methods; 6 were found to produce STa, while 16 did not. When 26 fecal samples were tested for the presence of STa, 10 were negative and 12 were positive by both assays. One of the remaining four samples gave questionable positive results by both the suckling mouse assay and the ELISA, but E. coli isolated from this sample gave positive results by both tests. The remaining three samples were negative by the suckling mouse assay, but gave questionable positive results by the ELISA. E. coli isolates from these three samples were always negative by both assays. The ELISA used in this study provides a reliable and convenient method for diagnosing STa-producing enterotoxigenic E. coli of porcine origin.