Simultaneous Detection of Escherichia coli O157:H7 and Salmonella Typhimurium: The Use of Magnetic Beads Conjugated with Multiple Capture Antibodies

Streptavidin-coated magnetic beads were conjugated with biotinylated capture antibodies to both Escherichia coli O157:H7 and Salmonella Typhimurium to form multi-pathogen capture immunomagnetic beads (IMB-M). The efficacy of these beads was investigated in both pure and mixed culture suspensions, as well as in inoculated spinach and ground beef. Using dual-label time-resolved fluorescence, a sandwich immunoassay consisting of europium- and samarium-labeled detection antibodies was used to measure the capture of E. coli and Salmonella, respectively. IMB-M was just as effective as the mixture of IMB against E. coli and Salmonella in capturing both organisms in pure culture and E. coli in mixed culture. Capture of Salmonella in mixed culture by IMB-M resulted in lower fluorescent signals, but comparable detection limit. In inoculated food samples, IMB-M was just as effective as the mixture of IMB specific for both target organisms in detecting 1 cfu/g of E. coli and 100 cfu/g of Salmonella after a 6-h enrichment at 37 °C. Multi-pathogen capture IMB have the potential to be convenient and important tools for multi-pathogen detection.