Comparative Validation Study to Demonstrate the Equivalence of a Minor Modification to AOAC Official Method 2005.05 Assurance GDS® Shiga Toxin Genes (O157) Method to the Reference Culture Method: 375 Gram Sample Size

The Assurance GDS® Shiga Toxin Genes (O157), AOAC Official MethodSM 2005.05, has been modified to include a larger sample size of 375 g. A methods comparison study was conducted to demonstrate the equivalence of this modification to the reference culture method. Ninety samples and controls, representing three foods, were analyzed. Results show no statistically detectable difference between the Assurance GDS Escherichia coli O157:H7 assay and the reference culture methods for the detection of E. coli O157:H7, other than the low level of inoculation for leaf lettuce for which the GDS gave noticeably higher recovery [difference in Probability of Detection between candidate methods (dPODc = +0.45)]. There were also suggestions of moderate differences (dPODc = +0.15 to +0.20) for ground beef and the high level of leaf lettuce, but the study size was too small to detect differences of this size. Results showed that the Assurance GDS Shiga Toxin Genes (O157) method is equivalent to the reference culture methods for the detection of Shiga toxigenic E. coli O157:H7.