EVALUATION OF A COMMERCIAL ENZYME-IMMUNOASSAY (EHEC-TEK) FOR DETECTING ESCHERICHIA-COLI O157 IN BEEF AND BEEF PRODUCTS

A commercial enzyme immunoassay system (EHEC-Tek) was compared with im munomagnetic separation followed by culture to cefixime-tellurite-sorb itol MacConkey agar (IMS/C) for detecting Escherichia coli O157 in art ificially inoculated beef samples and naturally contaminated beefburge rs. The EHEC-Tek assay used modified E. coli broth supplemented with n ovobiocin (mECn) as a primary enrichment medium, followed by immunomag netic separation, secondary enrichment of magnetic beads in tryptone s oya broth supplemented with acriflavine, followed by a standard monocl onal antibody-based immunoassay to detect O157 antigen. Twelve diverse strains of E. coli O157 were used to inoculate samples of minced beef in triplicate at each of three different concentrations (50, 5 and 0. 5 cfu 25 g(-1)). When the 108 samples of minced beef were examined, th ere was complete agreement between EHEC-Tek and IMS/C on 87 samples. T en samples were positive only by IMS/C and 11 samples were positive on ly by EHEC-Tek, such discrepant results occurring mainly at lower inoc ulum levels; of the latter 11, eight were confirmed culturally as cont aining E. coli O157. Five beefburgers naturally contaminated with E. c oli O157 at c. 2 g(-1) were negative by both EHEC-Tek and IMS/C after primary enrichment in mECn, but when the primary enrichment medium was buffered peptone water supplemented with vancomycin, cefixime and cef sulodin (BPW-VCC) E. coli O157 was detected in four out of five sample s by EHEC-Tek and five out of five samples by IMS/C. The EHEC-Tek immu noassay is a technically simple and sensitive method for detecting E. coli O157 in beef, and requires a minimum of microbiological expertise for its performance: the assay is improved by use of BPW-VCC in place of mECn as the primary enrichment medium. (C) 1996 Academic Press Lim ited