IMMUNOMAGNETIC SEPARATION AND FLOW-CYTOMETRY FOR RAPID DETECTION OF ESCHERICHIA-COLI O157-H7

A rapid method for detecting Escherichia coli O157:H7 combining immuno magnetic beads (LMB) and flow cytometry was developed. Labeling antige ns separated by IMB with fluorescent antibody enabled the detection of < 10(3) CFU bacteria per mi in pure culture. The optimum concentratio n of magnetic beads for flow cytometry was lower (ca. 10(5) particles per ml) than that reported for conventional IMB assay (more than 6 x 1 0(6) to 8 x 10(6) particles per ml). Immunomagnetic separation and flo w cytometry (IMFC) were evaluated for detecting E. coli O157:H7 in the presence of a competing microorganism and for detecting antibodies in potassium phosphate buffer. The total assay time from separating anti gens with IMB to analyzing with flow cytometry was about 1 h. IMFC det ected 10(3) to 10(4) CFU of E. coli O157:H7 per mi in ground beef enri chment broth and could effectively discriminate between E. coli O157:H 7 and competing natural flora. The new assay system provides another a pproach to separation and detection of low populations of pathogens an d shows potential for detecting low concentrations of toxins and other soluble antigens directly from food in a short time.