Luminescent methods to detect viable and total Escherichia coli O157:H7 in ground beef

Escherichia coli O157:H7 was inoculated into ground beef. Samples were incubated in E. coli broth plus novobiocin growth media at 37C for 5 h. Bacteria were captured by magnetic beads coated with anti-E. coli O157:H7 antibodies and were treated with menadione, a membrane-permeable electron-transfer shuttering reagent, to oxidize the cellular-nicotinamide adenine dinucleotide phosphate (NAD(P)H). Alternatively, bead-captured bacteria were sandwiched by second anti-E. coli O157:H7 antibodies labeled with peroxidase. The level of NAD(P)H and the enzyme activity of antibody-bound peroxidase were then measured by luminol-linked luminescence. The treatment of the E. coli O157:H7 with a bacterial protein extraction reagent diminished the luminescence associated with cellular NAD(P)H but not the luminescence associated with the sandwiched peroxidase label. Thus, the NAD(P)H-linked luminescence, not the luminescence that was associated with the sandwiched complexes, was related to the viability of the E. coli O157:H7.