title: Fate of Shiga toxin-producing O157:H7 and non-O157:H7 Escherichia coli cells within refrigerated, frozen, or frozen then thawed ground beef patties cooked on a commercial open-flame gas or a clamshell electric grill.
abstract: Both high-fat and low-fat ground beef (percent lean:fat = ca. 70:30 and 93:7, respectively) were inoculated with a 6-strain cocktail of non-O157:H7 Shiga toxin-producing Escherichia coli (STEC) or a five-strain cocktail of E. coli O157:H7 (ca. 7.0 log CFU/g). Patties were pressed (ca. 2.54 cm thick, ca. 300 g each) and then refrigerated (4°C, 18 to 24 h), or frozen (-18°C, 3 weeks), or frozen (-18°C, 3 weeks) and then thawed (4°C for 18 h or 21°C for 10 h) before being cooked on commercial gas or electric grills to internal temperatures of 60 to 76.6°C. For E. coli O157:H7, regardless of grill type or fat level, cooking refrigerated patties to 71.1 or 76.6°C decreased E. coli O157:H7 numbers from an initial level of ca. 7.0 log CFU/g to a final level of ≤1.0 log CFU/g, whereas decreases to ca. 1.1 to 3.1 log CFU/g were observed when refrigerated patties were cooked to 60.0 or 65.5°C. For patties that were frozen or freeze-thawed and cooked to 71.1 or 76.6°C, E. coli O157:H7 numbers decreased to ca. 1.7 or ≤0.7 log CFU/g. Likewise, pathogen numbers decreased to ca. 0.7 to 3.7 log CFU/g in patties that were frozen or freeze-thawed and cooked to 60.0 or 65.5°C. For STEC, regardless of grill type or fat level, cooking refrigerated patties to 71.1 or 76.6°C decreased pathogen numbers from ca. 7.0 to ≤0.7 log CFU/g, whereas decreases to ca. 0.7 to 3.6 log CFU/g were observed when refrigerated patties were cooked to 60.0 or 65.5°C. For patties that were frozen or freeze-thawed and cooked to 71.1 or 76.6°C, STEC numbers decreased to a final level of ca. 1.5 to ≤0.7 log CFU/g. Likewise, pathogen numbers decreased from ca. 7.0 to ca. 0.8 to 4.3 log CFU/g in patties that were frozen or freeze-thawed and cooked to 60.0 or 65.5°C. Thus, cooking ground beef patties that were refrigerated, frozen, or freeze-thawed to internal temperatures of 71.1 and 76.6°C was effective for eliminating ca. 5.1 to 7.0 log CFU of E. coli O157:H7 and STEC per g.
authors.affiliation: Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA. John.Luchansky@ars.usda.gov
authors.forename: John B
authors.initials: JB
authors.lastname: Luchansky
authors.forename: Anna C S
authors.initials: AC
authors.lastname: Porto-Fett
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Shoyer
authors.forename: John
authors.initials: J
authors.lastname: Phillips
authors.forename: Vivian
authors.initials: V
authors.lastname: Chen
authors.forename: Denise R
authors.initials: DR
authors.lastname: Eblen
authors.forename: L Victor
authors.initials: LV
authors.lastname: Cook
authors.forename: Tim B
authors.initials: TB
authors.lastname: Mohr
authors.forename: Emilio
authors.initials: E
authors.lastname: Esteban
authors.forename: Nathan
authors.initials: N
authors.lastname: Bauer
mesh_terms: D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D003296:Cooking / Q000379:methods; D019453:Escherichia coli O157 / Q000254:growth & development*; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D008461:Meat Products / Q000382:microbiology*; D022621:Shiga Toxin / Q000378:metabolism; D054323:Shiga-Toxigenic Escherichia coli / Q000254:growth & development*; D013696:Temperature
chemical_list: D022621:Shiga Toxin