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P1-16 Detecting Escherichia coli O157:H7 in Composite 375 g Raw Ground Beef Samples Using the DuPont™ BAX® System Method

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Steven Hoelzer, DuPont Nutrition & Health, Wilmington, DE
Julie Weller, DuPont Nutrition & Health, Wilmington, DE
Nisha Corrigan, DuPont Nutrition & Health, Wilmington, DE
Stacy Stoltenberg, DuPont Nutrition & Health, Wilmington, DE
Morgan Wallace, DuPont Nutrition & Health, Wilmington, DE
Jacqueline Harris, DuPont Nutrition & Health, Wilmington, DE
Krystal Shortlidge, DuPont Nutrition & Health, Wilmington, DE
Introduction:  Composite sample testing is quickly becoming the industry-accepted method for monitoring the incidence of Escherichia coli O157:H7 in non-intact raw beef, including beef trimmings and ground beef. Mandating a representative 60 – 6.25 g sub-samples per lot of beef trim, a 375 g analytical test portion is likely to be implemented for destined raw finished products, which are at further risk for contamination throughout grinding and processing operations. 

Purpose: In response to increasing industrial sample sizes, the DuPontTM BAX® System for Real-Time Escherichia coli O157:H7 was validated for 375 g analytical portions against the USDA-FSIS MLG 5.07.

Methods:   Ground beef patties obtained from local retail outlets (Wilmington, DE) were artificially inoculated with Escherichia coli O157:H7. Following a 72 hour cold stress, reference method samples were enriched in modified Tryptic Soy Broth (mTSB), whereas alternative method samples were enriched in mTSB with 2 mg/l of novobiocin (mTSB+n). All samples were incubated at 42 ± 1°C for 12-22 hours, and culture confirmed as outlined in USDA-MLG 5.07 regardless of presumptive PCR result after 22 hours.

Results:   PCR testing of mTSB+n enriched samples (n = 30) at 14 and 22 hours accurately detected all 9 culture positives. Similarly, all 15 presumptive positive samples at 14 and 22 hours of enrichment following the USDA reference method were culturally confirmed.

Significance: The data demonstrates that the PCR method for detection of E. coli O157:H7 in 375 g ground beef is equivalent to the reference culture method, providing customers the option of analyzing larger composite samples in a rapid manner to further reduce the risk of contaminated finished product.

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