Detection of immunomagnetic bead captured Escherichia coli O157:H7 by light addressable potentiometric sensor

A modified approach using a light addressable potentiometric sensor (LAPS) method to detect Escherichia coli O157:H7 in solutions is described, The bacterial cells were captured by the specific antibody coated on magnetic beads. The immuno paramagnetic beads (IMB) were then concentrated by a magnetic separator. Fluorescein-labeled anti E. coli antibody and urease-conjugated anti-fluorescein antibody were then used to label the cells captured by the beads. After labeling, the mixtures were rapidly filtered through 0.45 or 1.0 mu m nitrocellulose or polycarbonate filters. The production of NH3 from urea by the conjugated urease associated with the captured bacteria was then analyzed. The results indicate that IMB approach can be used to increase the specificity of the LAPS method for pathogenic bacteria detection. With this procedure, the presence of about one E. coli O157:H7 CFU per g of hamburger meat can be detected after a 6 h incubation.