A SOLID-PHASE FLUORESCENT CAPILLARY IMMUNOASSAY FOR THE DETECTION OF ESCHERICHIA-COLI O157-H7 IN-GROUND BEEF AND APPLE CIDER

A solid-phase fluorescence-based immunoassay was developed for the det ection of Escherichia coli O157:H7 using an antigen down competition f ormat. A soft glass capillary tube served as the solid support, to whi ch heat-killed E. coli O157:H7 were adsorbed. Polyclonal anti-E. coli O157:H7 antibody, conjugated with biotin, was used and the bound antig en-antibody complex was detected using avidin molecules labelled with Cy5, a fluorescent cyanine dye. Any E. coli O157:H7 in the sample woul d compete with the formation of this complex, reducing fluorescence. T his assay was tested for sensitivity with spiked ground beef and apple cider samples. The minimum detectable number of cells present in the initial inoculum was calculated to be approximately 1 colony-forming u nit (cfu) per 10 g of ground beef when samples were enriched in modifi ed EC broth for 7 h at 37 degrees C. The minimum detectable number of cells for the apple cider samples was calculated to be approximate to 0.5 cfu ml(-1). The E. coli cells in the cider samples were captured w ith immunomagnetic beads, incubated for 7 h in the enrichment broth, a nd detected with the solid phase fluorescence immunoassay.