Amperometric detection of Enterobacteriaceae in river water by measuring β-galactosidase activity at interdigitated microelectrode arrays

Two simple methodologies are compared for the detection of faecal contamination in water using amperometry at gold interdigitated microelectrodes. They rely on the detection of β-galactosidase (β-gal) by redox cycling amperometry of the p-aminophenol (PAP) produced by the enzyme from the 4-aminophenyl β-d-galactopyranoside (PAPG) substrate. The use of phages as specific agents for the release of the bacteria-enclosed enzyme allowed the detection of 6 × 10⁵ CFU mL⁻¹Escherichia coli in 2 h without any pre-enrichment or preconcentration steps. Better limits of detection were achieved for the second strategy in the absence of phages. In this case, bacteria were enriched in the presence of both β-d-1-thiogalactopyranoside (IPTG) and substrate but in the absence of phages. Under such experimental conditions, 5 × 10⁴ CFU mL⁻¹E. coli could be detected after 2 h of incubation, while 7 h of incubation were enough to detect down to 10 CFU mL⁻¹ in river water samples. This represents a straightforward one-step method for the detection of faecal contamination that can be conducted in a single working day with minimal sample manipulation by the user.