Capture of Escherichia coli O157:H7 Using Immunomagnetic Beads of Different Size and Antibody Conjugating Chemistry

Immunomagnetic beads (IMB) were synthesized using anti-Escherichia coli O157 antibodies and magnetic beads of two different sizes (1 μm and 2.6 to 2.8 μm) that contained a streptavidin coating, activated carboxyl groups or tosylated surfaces. The synthesized IMB, together with a commercially available IMB, were used to capture different strains of E. coli O157:H7 and E. coli O157:NM. The E. coli capture was measured by the time resolved fluorescence (TRF) intensity using a sandwich assay which we have previously demonstrated of having a sensitivity of 1 CFU/g after 4.5 hour enrichment [1]. The analyses of measured TRF intensity and determined antibody surface concentration indicated that larger beads provided higher response signals than smaller beads and were more effective in capturing the target of interest in pure culture and ground beef. In addition, while each type of IMB showed different favorable capture of E. coli O157:H7, streptavidin-coated IMB elicited the highest response, on average. Streptavidin-coated IMB also provided an economic benefit, costing less than $0.50 per assay. The results could be used to guide the proper choice of IMB for applications in developing detection processes for E. coli O157:H7.