Purpose: Utilize a high-level biocontainment processing facility containing industry-scale beef grinding equipment to conduct inoculated studies to characterize distribution of contamination, and our ability to detect the contamination, during ground beef manufacturing.
Methods: A cocktail of STEC serotypes (O26, O111, O45, O103, O121 and O145) was inoculated onto a 908 g piece of beef trim (yielding 8.9 and 5.8 log CFU/g of the inoculated trim for runs 1 and 2, respectively). This inoculated portion was placed into a commercial grinder followed by grinding two combos of beef trim. The meat was ground, blended, re-ground and chub packaged. Samples (375 g) were collected sequentially after each 45 kg portion of first grind, and every 20thfive-pound chub. Samples were enriched and STEC presence was determined using PCR.
Results: Run 1 (high inoculation level) samples were STEC positive at all sampling points. For run 2 (low level), 16 of the first 17 samples from first grind were positive and only one of the remaining 15 samples was positive. Run 2 chub samples were mostly negative (30/34).
Significance: Initial level of STEC contamination of isolated portions of beef trim entering a grinder greatly impacts the distribution levels and our ability to detect contamination in final chub packages. When a portion of trim is heavily contaminated and ground/blended/packaged, as in run 1, the entire system becomes contaminated and all samples are positive by PCR. At a lower contamination level, contamination in the grinder appears to dilute STEC to below detection after approximately one combo being ground; however, the blending and packaging process results in further dilution and yields only sporadic positives in finished chubs.