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Improvement and Validation of a DNA Microchip-Based Test for Rapid and Simultaneous Detection of Six Food-Borne Pathogens in Food Samples


Current diagnostic assays only allow for detection of a single pathogen at a time in food samples. However, there are a number of food-borne pathogens that are today's major public concerns. The DNA chip or microarray-based technology allows for simultaneous detection of large numbers of pathogens in a single sample. In previous projects, a prototype microarray-based test was developed for simultaneous detection of six common food-borne bacterial pathogens in a single test, including Shiga toxin-producing Escherichia coli (STEC), E. coli serotype O157:H7, Salmonella, Salmonella typhimurium DT104, Listeria monocytogenes and Campylobacter. The purpose of this project was to improve, optimize and validate the prototype microchip and associated procedures so that the chip-based test can eventually be used in diagnostic settings.
The system was improved, optimized and validated for its specificity using 771 target and 248 non-target microorganisms. The microchip results demonstrated correct identification of all the organisms tested. The detection limits of the system were 50 -1000 CFU/mL of pre-enrichment broth when spiked milk, lettuce, ground beef and ground pork samples were used. The system was also evaluated using 1012 pre-enriched food broths that were derived from 512 naturally contaminated foods, and 40 fecal samples. The percentages of correlation between cultural and the PCR-microchip methods for positive samples were 77% for Campylobacter, 91% for Salmonella, 91% for L. monocytogenes and 87% for E. coli, and for negative samples were 97%, 84%, 85% and 90% for the four organisms respectively. In addition, customized software was created to facilitate data calculation, interpretation and reporting.

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Expected Impact of Project Outcomes on Food Safety in Ontario: The project resulted in a chip-based test and its associated software that can potentially be used for rapid, specific and simultaneous detection of six food-borne pathogens in a single test in food samples. The availability of such a test will allow diagnostic labs to provide faster and cost-effective results to agri-food industries and consumers and provide an avenue to enhance the safety of Ontario's food supplies. This will also allow testing laboratories and government inspection staff to conduct risk assessment studies in a cost-effective and systematic manner in support of monitoring and surveillance activities and enforcement of regulatory programs.
<P> For more information, please visit the <a href="; target="_blank">Ontario Ministry of Agriculture, Food & Rural Affairs (OMAFRA) Food Safety Research Program</a>.

Chen, Shu
University of Guelph
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