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 beta-galactosidase activity is reported. The method relies on the detection of phenol released after the hydrolysis of phenyl P-D-galactopyranoside (PG) by beta-galactosidase. Under the optimized PG concentration and pH (4.0) values, a detection limit of 1.2 x 10(-3) unit of beta-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 x 10(6) 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 beta-D-thiogalactopyranoside for the enzyme activity induction, and 10 mu g mL(-1) polyinyxin 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.