P3-40 Independent Evaluation of a Commercial STEC Method for the Detection of Shiga Toxin-producing Escherichia coli in Ground Beef and Beef Trim

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Leslie Thompson, AEGIS FOOD TESTING Laboratories, North Sioux City, SD
Michelle Montgomery, Gelita, Sioux City, IA
Introduction: Shiga toxin-producing Escherichia coli (STEC) have been implicated in numerous foodborne outbreaks. With the implementation of routine testing by the USDA of additional serotypes of STEC in beef, a validated commercially available tested method is needed for the rapid detection of all regulated STEC organisms.

Purpose: The objective of this study was to evaluate the Bio-Rad iQ-Check<sup>®</sup> Real-Time PCR STEC method for the detection of inoculated Shiga toxin-producing Escherichia coli in ground and raw beef trim in comparison to the USDA FSIS MLG 5B.02, 5.06 and 5A.02 methods.

Methods: Portions of ground and beef trim were inoculated individually at low (0.2-2.0 cells/25g) or high (2.0-10 cells/25 g) inoculation levels with 5 different serotypes of E. coli.  The 25 g samples were combined with 350 g or 300 g of uninoculated beef for analysis with the iQ-Check and USDA FSIS MLG methods, respectively.

After 10 and 12 h of incubation in a 1:4 dilution of STEC Enrichment Broth, the samples tested with the iQ-Check method were analyzed with the kit for presence of stx and eae genes followed screening for the USDA “Top 7” O groups using the kit if the samples contained stx and eae.  The samples tested with the USDA FSIS MLG 5B.02/03 or 5A.02 methods were analyzed with the primer and probe sets as prescribed by the method or with BAX®E. coli O157 MP test. All samples were confirmed for the presence of target STEC organisms regardless of the screening result using the FSIS MLG 5B-02/03 and 5.06 methods.

Results: For inoculated beef trim and ground beef, the commercial method performed statistically as well as the USDA FSIS MLB 5B.02/03, 5.06, and 5A.02 methods for the detection of Shiga toxin-producing E. coli.

Significance: The commercial method provides a commercially available option to detect STEC in beef in as little as 10 h.