Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2006
Publication Date: 5/20/2006
Citation: Guerini, M.N., Arthur, T.M., Shackelford, S.D., Koohmaraie, M. 2006. Evaluation of Escherichia coli O157:H7 growth media for use in test-and-hold procedures for ground beef processing. Journal of Food Protection. 69(5):1007-1011.
Interpretive Summary: The bacterial pathogen Escherichia coli O157:H7 has been a concern to the meat processing industry for the last twenty years. In the early 1990s a ground beef-related E. coli O157:H7 outbreak caused hundreds of illnesses and four deaths. In response to these events, the USDA Food Safety and Inspection Service (FSIS) declared E. coli O157:H7 an adulterant in ground beef (USDA-FSIS Directive 10,010.01). In response to the Directive, and beginning in the mid-1990s, the beef industry has used a process called test-and-hold to sample beef trim and ground beef to test for the presence of E. coli O157:H7. If the bacterium is identified, the product is removed from any further processing so that it never reaches the end consumer. This report describes the results of experiments comparing E. coli bacteriological enrichment media for use in this process. In total, 12 media were tested to determine the optimal growth conditions, best performing media, and whether the test-and-hold process could be made more user-friendly. We found that the optimal growth condition for many of the media included an incubation at 42 deg C without shaking. The eight best media were buffered peptone water/SOC (BPW/SOC), NZYM, SDI RapidChek, EHEC8, Neogen Reveal 8, BAX, BAX-MP, and tryptic soy broth (TSB). TSB was the easiest to prepare, had a wide application base, and was the least expensive. Further work examined the efficacy of changing the volume of medium used in the test-and-hold procedure to see if a smaller volume of medium could be used and thus make the process more user-friendly. Traditionally, the test-and-hold process uses 3.375 liters of media for every 375-g sample tested. Based on the data presented in this report we found that 1 liter of TSB can be used to enrich 375 g of ground beef rather than the use of the conventional 3.375 liters. These results demonstrate that beef processors can use a low cost medium, namely TSB, and reduce the amount of medium used to enrich for possible contaminating E. coli O157:H7 while maintaining a high level of accuracy in the testing of beef trim and ground beef.
Technical Abstract: Since the mid-1990s the beef industry has used a process called test-and-hold, wherein beef trim and ground beef are tested to keep Escherichia coli O157:H7-contaminated products out of commerce. Current E. coli O157:H7 detection methods rely on a threshold level of bacteria growth for detection and the time needed to reach this threshold is dependent on the growth medium used. This report describes the results of experiments comparing E. coli bacteriological enrichment media for growth and doubling time. Twelve media were examined including: buffered peptone water (BPW), SOC, BPW/SOC, NZYM, SDI RapidChek, EHEC8, Neogen Reveal 8, BAX, BAX-MP, modified EC broth, Nutrient media, and tryptic soy broth (TSB). All media were tested at 37 deg C or 42 deg C under static or shaking (120 rpm) conditions. The eight media resulting in the highest total CFU/ml and most rapid doubling times were BPW/SOC, NZYM, SDI RapidChek, EHEC8, Neogen Reveal 8, BAX, BAX-MP, and TSB. A direct comparison of these eight found that BPW/SOC, NZYM, SDI RapidChek, BAX-MP and TSB performed the best. Of these, TSB was the easiest to prepare, had a wide application base, and was the least expensive. In the test-and-hold process the normal ratio of medium to product is 1:10. This study found that a 1:3 ratio worked as well as a 1:10 ratio. Processors using test-and-hold could use 1 liter of TSB to enrich for E. coli O157:H7 in a 375-g sample instead of the usual 3.375 liters, thus saving reagents, time, and labor while maintaining accuracy.