Validation Study of a Novel Secondary Screening Assay for the Identification of Individual Top 6 Shiga Toxigenic E. coli (STEC) Serogroups in Various Meat Products

Introduction: Meat products, such as beef trim and ground beef have been identified as a source of past non-O157 Shiga toxigenic E. coli (STEC) outbreaks.  This study proposed a novel secondary screening method, Assurance GDS^®MPX ID for Top STEC, utilizing Immunomagnetic Separation (IMS) and Polymerase Chain Reaction (PCR) to identify the individual top 6 STEC non-O157 serogroups in 14 h or less. 

Purpose: To demonstrate the equivalence of Assurance GDS MPX ID for Top STEC to the reference culture method for the identification of  the Top 6 non-O157 STEC serogroups in STEC positive meat samples.

Methods: Various meat matrices including beef trim, ground beef and pre-formed beef patties were included in the study.  One hundred eighty-five samples, ranging in size from 25 g to 375 g, were inoculated with low levels of each of the Top 6 non-O157 STEC and enriched in mEHEC^® for 10 – 18 h at 42°C.  After initial analysis with Assurance GDS MPX for Top 7 STEC all positive samples were then analyzed using Assurance GDS MPX ID for Top STEC and the reference culture method, USDA FSIS MLG 5.06.  Inclusivity and exclusivity of Assurance GDS was determined by analyzing 128 strains of Top 6 STEC and 69 strains of potential cross-reacting organisms, including non-E. coli and E. coli non-STEC serogroups.    

Results: Assurance GDS identified the following Top STEC serogroups: O103 (10 samples), O121 (41 samples), O145 (25 samples), O26 (9 samples), O111 (34 samples) and O45 (66 samples) from the original 185 samples.  There was a 100% agreement between Assurance GDS MPX ID for Top STEC and the USDA MLG reference confirmation method.

Significance: This new secondary screening method provides the industry with a faster option for identifying Top 6 STEC serogroups than culture methods, while retaining the necessary accuracy.