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

Abstract

A competitive enzyme-linked immunosorbent assay (ELISA) was compared with the conventional suckling mouse assay for the identification of heat-stable enterotoxin (ST(a)) 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 ST(a) by both tests. Identical results were obtained when 22 primary agar cultures were screened for ST(a) production by both methods; 6 were found to produce ST(a), while 16 did not. When 26 fecal samples were tested for the presence of ST(a), 10 were negative and 12 were positive by both assays. One of the remaining 4 samples gave questionable 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 3 samples were negative by the suckling mouse assay, but gave questionable positive results by the ELISA. E. coli isolates from these 3 samples were always negative by both assays. The ELISA used in this study provides a reliable and convenient method for diagnosing ST(a)-producing enterotoxigenic E. coli of porcine origin.