Rapid detection of Escherichia coli by flow injection analysis coupled with amperometric method using an IrO2-Pd chemically modified electrode

An amperometric method for the rapid detection of Escherichia coli (E. coli) by flow injection analysis (FIA) using an IrO2-Pd chemically modified electrode (CME) was developed in this paper. The method is based on a good marker beta-D-galactosidase which was found in E. coli strains. beta-D-galactosidase was produced by the induction of isopropyl beta-D-thiogalactopyranoside (IPTG) and released from E. coli cells through the permeabilization of both polymyxin B nonapeptide and lysozyme to E. coli cells wall. The released P-beta-galactosidase could catalyze the hydrolysis of the substrate p-aminophenyl P-beta-galactopyranoside (PAPG) in the culture medium to produce 4-aminophenol which was proportional to the concentration of E. coli. Hence, E coli could be detected by the determination of 4-aminophenol. An IrO2-Pd CME, which showed high sensitivity in determination of 4-aminophenol, was prepared as the electro-detector in FIA. The amplified response current of 4-aminophenol obtained at the IrO2-Pd CME was linear with the concentration of E. coli ranging from 2.0 x 10(2) to 1.0 x 10(6) cfu/mL, the detection limit of this method to E. coli was 150 cfu/mL and the complete assay could be performed in 3 h. (c) 2007 Elsevier B.V. All rights reserved.