Purpose: These studies independently validated AOAC-RI approved Roka Atlas EG2 Combo STEC Detection assay for detection of Big Six STEC in trim, ground and finely textured beef matrices.
Methods: Eight studies were conducted across 3 matrices. For beef trim, O26, O103, O111 and O121 were utilized. Raw trim was portioned into 30, 375-g samples, inoculated with a subfractional or high level 3-strain cold-stressed cocktail of the serogroup and enriched for 8 - 24 h at 1:4 in modified tryptic soy broth with casamino acids (mTSB+CAA) at 42°C. At 8 and 10 h, individual samples were taken for assay and 1 ml combined with 4 ml of non-inoculated enrichment to form 20 low and 5 high level pooled samples. Pooled samples were assayed at 8 and 10 h. For ground beef, O26 and O145 were similarly processed at 1:5 and assayed at 8, 10 and 12 h including pooling with 1 ml to 2 ml as above. Finely textured beef was evaluated with O26 and O45 at 1:5 and assayed at 10 and 12 h without pooling. Aerobic plate counts were conducted by pour plate method. A heat step was utilized in processing for Atlas EG2 Combo 8 hour samples. All samples were confirmed with USDA MLG 5B.04.
Results: Of 890 samples, the Atlas EG2 Combo reported 585 positive and 305 negative results. Two false negative results were associated with serogroup O103 in an individual and paired, pooled beef trim sample and one O26 in ground beef at 8 hours from low level replicates. Overall, the assay demonstrated 99.66% sensitivity and 99.34% specificity.
Significance: The Atlas EG2 Combo STEC Detection Assay is a sensitive and specific method for detection of Big Six STEC in trim, ground and finely textured beef matrices.