Use of a Shiga toxin (Stx)-enzyme-linked immunosorbent assay and immunoblot for detection and isolation of Stx-producing Escherichia coli from naturally contaminated beef

The purpose of this study was to evaluate an enzyme-linked immunosorbent as say (ELISA) and an immunoblot procedure for detection and isolation of Shig a toxin-producing Escherichia coli (STEC) from beef, and to correlate the p resence of STEC in beef with E. coli and total coliform counts. A total of 120 samples of boneless beef supplied to a meat processor in southern Ontar io were tested for the presence of STEC, E. coli, and total coliforms. Foll owing enrichment in modified tryptic soy broth, samples were screened for S higa toxin (Stx) by a Stx-ELISA and a Vero cell assay (VCA). Samples that w ere positive in the Stx-ELISA were subjected to the Stx-immunoblot for STEC isolation. Overall, 33.3% of samples were positive in the VCA, and 34.2% w ere positive in the Stx-ELISA. There was almost complete agreement between the Stx-ELISA and the VCA results (kappa = 0.98). The sensitivity and speci ficity of the Stx-ELISA with respect to the VCA were 100% and 98.75%, respe ctively. STEC were isolated by the Stx-immunoblot from 87.8% of the samples that were positive in the Stx-ELISA. The STEC isolates belonged to 19 sero types, with serotype 0113:H21 accounting for 10 of 41 isolates. No STEC of serotype O157:H7 were isolated. There was a significant correlation between E. coli counts and total coliform counts (Spearman correlation coefficient = 0.68, P < 0.01). The E. coli count was positively correlated with detect ion of STEC by both the Stx-ELISA and the VCA (P < 0.01).