Escherichia coli O157:H7 is one of the most commonly reported pathogens associated with microbial contamination of leafy greens. Since washing... Show moreEscherichia coli O157:H7 is one of the most commonly reported pathogens associated with microbial contamination of leafy greens. Since washing is a major postharvest processing step, microbial testing of spent wash water has been suggested as a good marker to determine the contamination status of the products. In this study, the efficiency of four commercial rapid methods (BAX®, IQ-Check, Reveal® and mini-VIDAS®) for detection of E.coli O157:H7 in lettuce wash water was evaluated in comparison with the FDA BAM method. The improvement of the detection sensitivity of these tests by immunomagnetic separation (IMS) technology and sample pre-concentration by Tangential Flow Filtration (TFF) was determined. Twenty-five ml of lab prepared lettuce wash water samples were spiked with 0, 1, 10, 100 CFU of E.coli O157:H7, and subjected to enrichment protocols recommended by each of the methods. The presence of E.coli O157:H7 in the enriched samples were then assayed by the test kits, either directly or after IMS (IMS-Pathatrix ™ or IMS-Dynabeads™) treatments. All four test kits and BAM were able to detect E.coli O157:H7 at levels as low as 1 CFU/25ml of wash water. IMS treatments did not lead to further improvement in detection sensitivity. Experiments were also performed to determine the feasibility of incorporating IMS and sample pre-concentration to achieve culture-free detection. Fifty ml of wash water samples were inoculated with E.coli O157:H7 at levels of 0 to 107 CFU and analyzed by the test kits either directly or after IMS-Pathatrix™ treatment. Additionally, 10 L of wash water either prepared in the lab or collected from a commercial fresh-cut processing facility were inoculated with 0 – 106 CFU of the pathogen and subjected to TFF concentration prior to IMS or test kit analyses. IQ-Check showed the highest sensitivity with a detection limit as low as 103 CFU/50ml, and, with IMS, achieved a sensitivity of 100 CFU/50ml. Combining TFF concentration and IMS, 10 L of lab prepared wash water can be tested with IQ-Check and achieve a detection limit of approx. 100 CFU/10 L within 6 hours. For 10L of industry spent wash water, IQ-check also showed the highest sensitivity but the results lacked consistency and required additional evaluations. M.S. in Food Safety and Technology, December 2011 Show less
