Enumeration of coliforms and Escherichia coli in frozen black tiger shrimp Penaeus monodon by conventional and rapid methods

Abstract

Conventional (most probable number, MPN) and rapid methods—including Chromocult® coliform agar (CCA), Fluorocult® LMX broth (LMX), and Petrifilm™ Escherichia coli count plates (PEC) for enumeration of coliforms and E. coli in frozen black tiger shrimp from Thailand were compared in order to assess the possibility of using one of the rapid methods for routine analysis. Enumeration of coliforms and E. coli from 18 samples of regular frozen black tiger shrimp and 156 samples of frozen black tiger shrimp experimentally contaminated with coliforms or E. coli at concentrations of ∼10, ∼10 2, and ∼10 3 CFU g −1 revealed that at the level of ∼10 CFU g −1, coliform numbers ranked as LMX>CCA>MPN=PEC and E. coli as MPN=LMX=PEC=CCA. At the level of ∼10 2 CFU g −1, coliform numbers ranked as LMX>MPN=PEC=CCA and E. coli as MPN=LMX>PEC=CCA. At the level of 10 3 CFU g −1, coliforms ranked as LMX>MPN=CCA>PEC and E. coli as MPN>LMX>CCA>PEC. Agreements with the conventional MPN method for coliforms were LMX 108%, PEC 87.2%, and CCA 91.2% and agreements for E. coli were LMX 101%, PEC 95.7%, and CCA 96.3%. Sensitivities (%) ranked LMX>MPN>CCA=PEC for coliforms and E. coli, whereas equal specificities (100%) of all methods for coliforms and E. coli were demonstrated. Rankings for the other parameters compared were: convenience, PEC>CCA=LMX>MPN; time to detection, MPN>LMX=PEC=CCA; expense, MPN=PEC>CCA>LMX; labor, MPN>LMX=CCA>PEC; accuracy for coliforms, PEC>CCA>MPN>LMX; and accuracy for E. coli, PEC=CCA>LMX>MPN.