Voltammetric measurement of Escherichia coli concentration through p-APG hydrolysis by endogenous β-galactosidase

This paper reports a facile electrochemical detection method for Escherichia coli (E. coli) that does not use DNA amplification or immunoassay. The detection principle is based on the activity of the β-galactosidase (β-gal) endogenous enzyme, which hydrolyzes p-aminophenyl-β-D-galactopyranoside (p-APG) into p-aminophenol. After E. coli consumes p-APG within 30 min, the remaining p-APG is oxidized on a gold electrode using cyclic voltammetry and square wave voltammetry. The β-gal expression level is increased through treatment with a β-gal expression inducer (isopropyl-β-D-thiogalactopyranoside), and the hydrolysis reaction of p-APG is facilitated through permeabilization treatment with sodium dodecyl sulfate. The calibration curve for E. coli has a working range of 102–104 colony-forming units per mL in nutrient broth buffer. The total assay time is less than 100 min. The successful application of this approach indicates the possibility of rapid detection.