Automated Dead-End Ultrafiltration for Concentration and Recovery of Total Coliform Bacteria and Laboratory-Spiked Escherichia coli O157:H7 from 50-Liter Produce Washes To Enhance Detection by an Electrochemiluminescence Immunoassay

Abstract

An automated concentration system (ACS) based on dead-end ultrafiltration was used in this study to concentrate bacteria, including Escherichia coli O157:H7, from 50-liter produce washes (PWs, sieved produce wash). Cells trapped in the filters were recovered in approximately 400 ml of buffer to create PW retentates (PWRs). Extent of concentration was determined by analyzing PWs and PWRs for total coliform bacteria and E. coli O157:H7 using standard methods. In addition, an electrochemiluminescence immunoassay was evaluated for detection of E. coli O157:H7 in spiked PWs and PWRs to demonstrate usefulness of the ACS for same-day detection. The levels of total coliform bacteria and E. coli O157:H7 in PWRs were higher than those in PWs by 1.85 ± 0.41 log most probable number per 100 ml and 1.82 ± 0.24 log CFU/ml, respectively. Electrochemiluminescence detection of E. coli O157:H7 was accomplished within 2 h using ACS concentration of lettuce and spinach wash water artificially spiked with the pathogen at levels as low as 0.36 log CFU/ml and 1.39 log CFU/ml, respectively. Detection of E. coli O157:H7 at 20.93 ± 0.15 log CFU/ml in lettuce wash occurred within approximately 6 h when a 4-h enrichment step was added to the procedure. Use of dead-end ultrafiltration increased bacterial concentrations in PWR and allowed same-day detection of low levels of E. coli O157:H7 in PW. This concentration system could be useful to improve the sensitivity of current rapid methods for detection of low levels of foodborne pathogens in PW water.