Rapid estimation of Escherichia coli in live marine bivalve shellfish using automated conductance measurement

Conductance measurement for quantitative estimations of Escherichia coli in live bivalve shellfish was evaluated as an alternative to the conventional most probable number (MPN) method used in France. The sensitivity of the two techniques was comparable. A single regression line (r = -0.968, P < 10(-6)) between log10 MPN and detection time (DT) was used to estimate E. coli concentrations for all shellfish examined. Estimation accuracy was +/- 0.92 log unit. Repeatability was better for DT than the log10 of MPN estimations (average coefficients of variation 2.7 and 9.3%, respectively). The conductance signal was attributable to E. coli in 96% of cases, and only 0.7% of E. coli cultures failed to exhibit a signal within 20 h. The conductance method reduces analysis handling time and is much easier to use than the MPN method. Moreover, results can be obtained within 5-9 h compared to 3 d for the MPN method.