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item Gehring, Andrew
item Tu, Shu I

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2004
Publication Date: 1/5/2005
Citation: Gehring, A.G., Tu, S. 2005. Enzyme-linked immunomagnetic electrochemical detection of live escherichia coli 0157:h7 in apple juice. Journal of Food Protection. 2005. p.146-149.

Interpretive Summary: Current methods for detecting bacteria are too time consuming to be used for routine testing of many food products. A novel method, termed enzyme-linked immunomagnetic electrochemistry (ELIME), is being developed to quickly detect pathogenic bacteria in less than one and a half hours. In the ELIME technique, small magnetic particles that are coated with antibodies (similar to those found in our bodies that fight diseases) specifically bind targeted bacteria in a solution. A magnetized electrochemical sensor is then placed in the solution, causing the bacteria associated particles to adhere tightly to its surface. The other components of the sample are washed off, and reagents are added which produce a chemical reaction with the captured bacteria. An instrument connected to the sensor subsequently produces a signal proportional to the number of bacteria present. This technique was demonstrated to detect about 5,000 live Escherichia coli O157:H7 bacteria in one milliliter of apple juice. When fully developed, this technology will help food producers and processors to reduce foodborne illnesses caused by pathogens by permitting rapid on site testing for bacterial contamination.

Technical Abstract: We describe the application of enzyme-linked immunomagnetic electrochemistry (ELIME) for the rapid detection of Escherichia coli O157:H7 in buffered apple juice. The ELIME technique entails “sandwiching” bacterial analyte between antibody-coated magnetic beads and an alkaline phosphatase-conjugated antibody. The beads (with or without bound bacteria) were localized onto the surface of magnetized graphite ink electrodes in a multi-well plate format. The enzyme substrate, 1-naphthyl phosphate, was added and conversion of substrate to an electroactive product was measured using electrochemical detection. Using this technique, detection of whole, live E. coli O157:H7 bacterial cells was achieved with a minimum detectable level of ca. 5 x 103 cells/ml in Tris-buffered saline or buffered apple juice in an assay time of ca. 80 min. With adjustment of pH, the ELIME response for the bacteria in either sampling medium was similar therefore indicating that apple juice components did not contribute to any discernible sample matrix effects.