Escherichia coli detection in vegetable food by a potentiometric biosensor

The present work describes the application of an antibody based biosensor for the determination of Escherichia coli cells in vegetable food. The presence of E. coli as a bioindicator of bacterial contamination—faecal one in particular—was detected using the potentiometric alternating biosensing (PAB) system based on a light addressable potentiometric sensor (LAPS) transducing element, detecting pH variations due to NH3 production by an urease–E. coli antibody conjugate. Commercial samples of vegetable—lettuce, sliced carrots, and rucola—were washed with peptone water at pH 6.8, blended either in a stomacher or in a sonicator, to detach bacterial cells and to recover them in the liquid medium. This liquid phase was analyzed both by PAB system and conventional colony forming units (CFUs) methods. The proposed PAB system appears to be very sensitive and fast, in comparison with conventional methods: concentration of 10 cells/ml were detected in an assay time of ca. 1.5 h, showing detection time from 10 to 20 times shorter than the conventional CFU procedure. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Escherichia coli; Potentiometric sensor; Immunoassay biosensor; Vegetable food