Simultaneous Immunomagnetic Separation Method for the Detection of Escherichia coli O26, O111, and O157 from Food...

We performed a simultaneous immunomagnetic separation (IMS) assay on Shiga toxin-producing Escherichia coli (STEC) serogroups O26, O111, and O157 with immunobeads coated with O26, O111, or O157 antibodies that were simultaneously added to an aliquot of food culture. We also compared the usefulness of CHROMagar STEC medium against various selective isolation agars designed to test for the three serogroups. Samples of sliced beef, ground beef, and radish sprout were artificially contaminated with STEC O26, O111, and O157 strains after incubation in enrichment broth and were subjected to conventional and simultaneous IMS assays. Simultaneous IMS did not affect the sensitivity of target cell detection. For STEC O26, O111, and O157 inoculated into the enriched samples of sliced beef and radish sprout, the detection ability of CHROMagar STEC was similar to or exceeded that of other isolation agars. However for STEC O157 inoculated into ground beef cultures, cefixime tellurite sorbitol MacConkey agar (CT-SMAC) was the superior detection medium. The performance of simultaneous IMS combined with CT-SMAC and CHROMagar STEC detection is similar to that of the Japanese standard method for isolating E. coli O26, O111, and O157. However, the proposed approach involves the same time, materials, and labor costs as the standard E. coli O157 reference procedure but allows detection of three E. coli serotypes rather than a single strain.