In-a-Day Electrochemical Detection of Coliforms in Drinking Water Using a Tyrosinase Composite Biosensor

A rapid method for the detection of fecal contamination in water based on the use of a tyrosinase composite biosensor for improved amperometric detection of -galactosidase activity is reported. The method relies on the detection of phenol released after the hydrolysis of phenyl -Dgalactopyranoside (PG) by -galactosidase. Under the optimized PG concentration and pH (4.0) values, a detection limit of 1.2 * 10-3 unit of -galactosidase/mL-1 was obtained. The capability of the sensor for the detection of Escherichia coli was evaluated using polymyxin B sulfate to allow permeabilization of the bacteria membrane. A detection limit of 1 * 106 cfu of E. coli mL-1 was obtained with no preconcentration or pre-enrichment steps. To improve the analytical characteristics for bacteria detection, the processes involving galactosidase induction during incubation and membrane permeabilization were optimized. Using 0.25 mM isopropyl -Dthiogalactopyranoside for the enzyme activity induction, and 10 g mL-1 polymyxin B sulfate as permeabilizer agent, it was possible to detect bacteria concentrations as low as 10 cfu mL-1 after 5 h of enrichment. The possibility of detecting E. coli at the required levels for drinking water quality assessment (1 cfu/100 mL) is demonstrated, the time of analysis being shorter than 6.5 h and involving a simple methodology.