title: Evaluation of Escherichia coli O157:H7 growth media for use in test-and-hold procedures for ground beef processing.
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 products contaminated with Escherichia coli O157:H7 out of commerce. Current O157:H7 detection methods rely on a threshold level of bacterial growth for detection, which is dependent on the growth medium used. Twelve media were examined for growth and doubling time: buffered peptone water (BPW), SOC (which contains tryptone, yeast extract, KCl, MgCl2, and glucose), buffered peptone water plus SOC (BPW-SOC), Bacto-NZYM, RapidChek E. coli O157:H7 medium, BioControl EHEC8 culture medium, Neogen Reveal for E. coli O157:H7--Eight Hour medium (Neogen Reveal 8), BAX System medium for E. coli O157:H7 (BAX) BAX System medium for E. coli O157:H7 MP (BAX-MP), modified E. coli broth, nutrient medium, and tryptic soy broth (TSB). All media were tested at 37 or 42 degrees C under static or shaking conditions. The eight media with the highest total CFU per milliliter and most rapid doubling times were BPW-SOC, NZYM, RapidChek, EHEC8, Neogen Reveal 8, BAX, BAX-MP, and TSB. The ability of these eight media to enrich E. coli O157:H7 in ground beef was further evaluated through time-course experiments using immunomagnetic separation. Of these media, 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. In this study, a 1:3 ratio worked as well as a 1:10 ratio. Processors using test-and-hold procedures 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.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, Nebraska 68933-0166, USA. guerini@email.marc.usda.gov
authors.forename: Michael N
authors.initials: MN
authors.lastname: Guerini
authors.forename: Terrance M
authors.initials: TM
authors.lastname: Arthur
authors.forename: Steven D
authors.initials: SD
authors.lastname: Shackelford
authors.forename: Mohammad
authors.initials: M
authors.lastname: Koohmaraie
mesh_terms: D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D003470:Culture Media / Q000737:chemistry* / Q000592:standards; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000302:isolation & purification; D005506:Food Contamination / Q000032:analysis*; D006801:Humans; D018189:Immunomagnetic Separation / Q000379:methods; D008461:Meat Products / Q000382:microbiology*; D012680:Sensitivity and Specificity; D013696:Temperature; D013997:Time Factors
chemical_list: D003470:Culture Media