IMMUNOMAGNETIC SEPARATION WITH MEDIATED FLOW-INJECTION ANALYSIS AMPEROMETRIC DETECTION OF VIABLE ESCHERICHIA-COLI O157

The coupling of an immunological separation (using immunomagnetic bead s) with amperometric now injection analysis detection of viable bacter ia is presented. Using a solution containing Escherichia coli 0157, th e electrochemical response with two different mediators [potassium hex acyanoferrate(III) and 2,6-dichlorophenolindophenol] was evaluated in the FIA system. Antibody-derivatized Dynabeads were used to selectivel y separate E. coli 0157 from a matrix The kinetics and the capacity pa rameters regarding the attachment of bacteria to the immunobeads were studied. The immunomagnetic separation was then used in conjunction wi th electrochemical detection to measure the concentration of viable ba cteria. A calibration curve of colony-forming units (du) against elect rochemical response was obtained. The detection limit for this rapid m icrobiological method was 10(5) cfu mL(-1), and the complete assay was performed in 2 h. Some advantages over ELISA methods are the direct d etection of viable cells (and not total bacterial load) and the need f or only one antibody (not enzyme-labeled), thus making the assay faste r (only one washing step is necessary) and less expensive.