Purpose: The purpose of this study was to determine the efficacy of five different sampling methods for detecting randomized STEC contamination in beef trim contained in single combo units.
Methods: Standard combo bins (1.1 x 0.9 x 1.1 m) were divided into 27 sectors (9 on the bottom, middle and top layers each). A STEC strain (O103, O145 or O157) was inoculated onto a 908 g piece of beef trim (ca. 3 log CFU/g) and placed in a randomized bin sector. The combo was then filled with non-inoculated beef trim. Sampling methods were N-60 surface excision, N-90 surface excision, N-60 core drill shaving, Cozzini core sampler, and purge. Meat samples (375 g composites) were combined with 1.5 L of mEHEC and enriched at 42°C for 18 h prior to PCR to determine STEC presence.
Results: Purge sampling was the most effective method, with 13/14 samples positive. Cozzini corer, N-60 core drill shaving, N-60 excision and N-90 excision methods resulted in 11/14, 9/14, 7/14 and 7/14 samples being positive, respectively. The purge sampling and Cozzini corer were superior combo sampling methods, because they were able to detect contamination in the lower combo sectors. The N-60 and N-90 excision sampling methods were effective if contamination was placed into one of the top or middle sectors, but only 3/12 samples were positive for bottom sector inoculated samples.
Significance: Sampling of beef trim is an important component of ground beef safety programs. Excision sampling of combos utilizing N-60 or greater is commonly utilized. Selection of a sampling method (purge sampling or deep coring) capable of contacting trim in the bottom half of combos will yield a greater probability of identifying STEC contaminated combos.