Molecular Detection of Escherichia coli and Salmonella spp. in Contaminated Ground Meat with Immuno-magnetic Beads and Loopamp Kit

Introduction: In the United States, sources of contaminated food is a major problem in affecting human health. The major contaminating organisms are E. coli-O157 and Salmonella spp., which are known to cause severe health complications like nausea, vomiting, stomach cramps and bloody diarrhea. A major requirement and challenge for the food industry is the rapid and accurate detection and identification of contaminating bacteria in food.

Purpose: Conventional “standard” methods are usually time consuming, require a minimum of 48 hours for detection and pose a threat for food industry in releasing products into the market. There is a great need for rapid food testing methods in the market that can efficiently detect contaminating bacteria. This modified method makes use of immuno-magnetic capture of contaminating bacteria in food and high sensitive detection using the LoopAmp kit for E. coli-O157 and Salmonella spp.

Methods: Ground turkey and ground beef from local stores were inoculated with concentrations 10¹, 10² and 10³ CFU/ml of E. coli-O157, Salmonella spp., or both. Samples were collected at 2 hrs, 4 hrs and 6 hrs after incubation in mTSB media at 42 °C. The samples are concentrated using immuno-magnetic beads, extracted and amplified with LoopAmp kit. Our current 6 hrs enrichment protocol with LoopAmp kit is currently in AOAC review and is considered as standard in this study.

Results: The LoopAmp results were comparable to USDA and FDA standard methods and shorten the “time-to-result” in detection. In ground meat samples, we detected E. coli-O157and Salmonella spp., to as low as 10¹ CFU/ml with 6 hrs enrichment samples. Using improved method with magnetic beads, we can detect as low as 10¹ CFU/ml in 4 hrs and 10³ CFU/ml in 2 hrs enrichment samples.

Significance: The use of magnetic beads in food samples has shown to produce sensitive and comparable results as with 6 hrs enrichment samples. Unlike most methods that require 8 hrs - 16 hrs enrichment time, this method can be used with a minimum 4 hrs enrichment time. This study has a great potential in rapid food testing and provides highly sensitive and comparable results with less “time-to-result."