Comparative Evaluation of the 3M™ Molecular Detection Assay Escherichia coli O157 (including H7) for the Detection of Escherichia coli O157 in Foods

Introduction: The 3M™ Molecular Detection Assay E. coli O157 (including H7) is designed for rapid and specific detection of E. coli O157 following 8-18 hours of enrichment. The assay uses a combination of isothermal amplification of unique DNA target sequences and bioluminescence to detect the amplified sequences. Presumptive positive results are reported in real-time while negative results are displayed upon completion of the assay.

Purpose: The purpose of this evaluation was to compare the 3M™ Molecular Detection Assay E. coli O157 (including H7) method to the FDA/BAM for spinach and sprouts and the USDA/FSIS-MLG method for raw ground beef.

Methods: The method comparison was conducted on three food matrices using the 3M™ test method and a reference method (FDA/BAM or USDA/FSIS-MLG). Each matrix was inoculated with a different strain of E. coliO157 and 20 replicates were analyzed at a fractionally positive level of 2.3-3.75 CFU/sample. Five control replicates were analyzed at 0 CFU/25g. For the new method, replicates were enriched in BPW (3M ISO formulation) for 8-18 hours at 41.5 ± 1°C. Produce enrichments (spinach 200 g, sprouts 25 g) were prepared as 1:10 dilutions and beef enrichments (325 g) as 1:4 dilutions. DNA was extracted and analyzed by the new assay, and replicates confirmed by the reference methods.

Results: No significant differences were observed between the new method and the reference methods as indicated by McNemar’s X² (> 3.84) for the three foods. For foods compared to the FDA/BAM, X² = 2.01 for spinach and 1.52 for sprouts. For foods compared to the USDA/FSIS-MLG, X²= 0.0 for raw ground beef.

Significance: For the foods evaluated, the 3M method demonstrated comparable results to the reference methods for the rapid, automated detection of E. coli O157.