Thermal Inactivation of Escherichia coli O157:H7 Isolated from Ground Beef and Bovine Feces, and Suitability of Media for Enumeration

1998 ◽  
Vol 61 (3) ◽  
pp. 285-289 ◽  
Author(s):  
M. ROCELLE S. CLAVERO ◽  
LARRY R. BEUCHAT ◽  
MICHAEL P. DOYLE
Keyword(s):  
Escherichia Coli ◽  
Thermal Inactivation ◽  
Ground Beef ◽  
Treatment Temperature ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Polyethylene Bags ◽  
D Values ◽  
Bovine Feces

Rates of thermal inactivation of five strains of Escherichia coli O157:H7 isolated from ground beef implicated in outbreaks of hemorrhagic colitis and five strains isolated from bovine feces were determined. Ground beef (22% fat, 10 g), inoculated with individual test strains at populations ranging from 6.85 to 7.40 log10 CFU g−1 of beef, was formed into patties (0.3 cm thick and 8.0 cm in diameter) and sealed in polyethylene bags. For each strain and treatment temperature (54.4, 58.9, 62.8, 65.6, or 68.3°C), 6 bags were simultaneously immersed into a recirculating water bath. Viable cells in patties heated for various lengths of time were enumerated by plating diluted samples on sorbitol MacConkey agar supplemented with 4-methylumbelliferyl-β-d-glucuronide (MSMA) and modified eosin methylene blue (MEMB) agar. Regardless of strain or treatment temperature, higher numbers of E. coli O157:H7 cells were generally recovered on MEMB agar than on MSMA, indicating the inferiority of MSMA as a recovery medium for quantitative determination of E. coli O157:H7 cells in heat-processed ground beef. Significantly (P ≤ 0.05) higher D values when enumeration was done using MEMB agar compared with MSMA. Mean D values for combined strain data at 54.4, 58.9, 62.8, and 65.6°C from cultures on MEMB agar were 123.90, 6.47, 0.62, and 0.20 min, respectively, whereas D values of 25.5, 5.21, 0.57, and 0.18 min were obtained at the same temperatures from cultures on MSMA. Results suggest that cooking ground beef patties to an internal temperature of 68.3°C for 40 s will inactivate at least 99.99% of E. coli O157:H7 cells; z values of 4.0 and 5.1°C were calculated from mean D values obtained from MEMB agar and MSMA, respectively, as recovery media. Differences in D values and z values existed among strains but rates of thermal inactivation do not appear to be correlated with the sources of the isolates.

Thermal Inactivation of Escherichia coli O157: H7, Salmonella senftenberg, and Enzymes with Potential as Time-Temperature Indicators in Ground Beef

1997 ◽  
Vol 60 (5) ◽  
pp. 471-475 ◽  
Author(s):  
ALICIA ORTA-RAMIREZ ◽  
JAMES F. PRICE ◽  
YIH-CHIH HSU ◽  
GIRIDARAN J. VEERAMUTHU ◽  
JAMIE S. CHERRY-MERRITT ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Thermal Inactivation ◽  
Ground Beef ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Triose Phosphate ◽  
Beef Products ◽  
Z Value ◽  
D Values ◽  
Salmonella Senftenberg

The USDA has established processing schedules for beef products based on the destruction of pathogens. Several enzymes have been suggested as potential indicators of heat processing. However, no relationship between the inactivation rates of these enzymes and those of pathogenic microorganisms has been determined. Our objective was to compare the thermal inactivation of Escherichia coli O157:H7 and Salmonella senftenberg to those of endogenous muscle proteins. Inoculated and noninoculated ground beef samples were heated at four temperatures for predetermined intervals of time in thermal-death-time studies. Bacterial counts were determined and enzymes were assayed for residual activity. The D values for E. coli O157:H7 were 46.10, 6.44, 0.43, and 0.12 min at 53, 58, 63, and 68°C, respectively, with a z value of 5.60°C. The D values for S. senftenberg were 53.00, 15.17, 2.08, and 0.22 min at 53, 58, 63, and 68°C, respectively, with a z value of 6.24°C. Apparent D values at 53, 58, 63, and 68°C were 352.93, 26.31, 5.56, and 3.33 min for acid phosphatase; 6968.64, 543.48, 19.61, and 1.40 min for lactate dehydrogenase; and 3870.97, 2678.59, 769.23, and 42.92 min for peroxidase; with z values of 7.41,3.99, and 7.80°C, respectively. Apparent D values at 53, 58, 63, and 66°C were 325.03, 60.07, 3.07, and 1.34 min for phosphoglycerate mutase; 606.72, 89.86, 4.40, and 1.28 min for glyceraldehyde-3-phosphate dehydrogenase; and 153.06, 20.13, 2.25, and 0.74 min for triose phosphate isomerase; with z values of 5.18, 4.71, and 5.56°C, respectively. The temperature dependence of triose phosphate isomerase was similar to those of both E. coli O157 :H7 and S. senftenberg, suggesting that this enzyme could be used as an endogenous time-temperature indicator in beef products.

Thermal Inactivation of Escherichia coli O157:H7 in Ground Beef Supplemented with Sodium Lactate†

2003 ◽  
Vol 66 (4) ◽  
pp. 664-667 ◽  
Author(s):  
LIHAN HUANG ◽  
VIJAY K. JUNEJA
Keyword(s):  
Escherichia Coli ◽  
Thermal Resistance ◽  
Thermal Inactivation ◽  
Heating Temperature ◽  
Ground Beef ◽  
Antimicrobial Effect ◽  
Sodium Lactate ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
D Values

A study was conducted to investigate the antimicrobial effect of sodium lactate (NaL) (0, 1.5, 3.0, and 4.5%) on the survival of Escherichia coli O157:H7 in 93% lean ground beef. Samples inoculated with a mixture of four strains of E. coli O157:H7 (107 to 108 CFU/g) were subjected to immersion heating in a water bath stabilized at 55, 57.5, 60, 62.5, or 65°C. Results of statistical analysis indicated that the heating temperature was the only factor affecting the decimal reduction times (D-values) of E. coli O157:H7 in 93% lean ground beef. The change in temperature required to change the D-value (the z-value) was determined as 7.6°C. The thermal resistance of this organism was neither affected by the addition of NaL nor by the interactions between NaL and temperature. Adding NaL to ground beef to reduce the thermal resistance of E. coli O157: H7 is therefore not recommended.

Thermal Process Validation for Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in Ground Turkey and Beef Products

2004 ◽  
Vol 67 (7) ◽  
pp. 1394-1402 ◽  
Author(s):  
R. Y. MURPHY ◽  
E. M. MARTIN ◽  
L. K. DUNCAN ◽  
B. L. BEARD ◽  
J. A. MARCY
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Thermal Inactivation ◽  
Ground Beef ◽  
Escherichia Coli O157 ◽  
Process Validation ◽  
E Coli ◽  
Beef Products ◽  
Air Impingement ◽  
D Values

At 55 to 70°C, thermal inactivation D-values for Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes were 19.05 to 0.038, 43.10 to 0.096, and 33.11 to 0.12 min, respectively, in ground turkey and 21.55 to 0.055, 37.04 to 0.066, and 36.90 to 0.063 min, respectively, in ground beef. The z-values were 5.73, 5.54, and 6.13°C, respectively, in ground turkey and 5.43, 5.74, and 6.01°C, respectively, in ground beef. In both ground turkey and beef, significant (P < 0.05) differences were found in the D-values between E. coli O157:H7 and Salmonella or between E. coli O157:H7 and L. monocytogenes. At 65 to 70°C, D-values for E. coli O157:H7, Salmonella, and L. monocytogenes were also significantly (P < 0.05) different between turkey and beef. The obtained D- and z-values were used in predicting process lethality of the pathogens in ground turkey and beef patties cooked in an air impingement oven and confirmed by inoculation studies for a 7-log (CFU/g) reduction of E. coli O157:H7, Salmonella, and L. monocytogenes.

Influence of Freezing and Freezing Plus Acidic Calcium Sulfate and Lactic Acid Addition on Thermal Inactivation of Escherichia coli O157:H7 in Ground Beef

2004 ◽  
Vol 67 (8) ◽  
pp. 1760-1764 ◽  
Author(s):  
TONG ZHAO ◽  
MICHAEL P. DOYLE ◽  
MAURICE C. KEMP ◽  
RHONDA S. HOWELL ◽  
PING ZHAO
Keyword(s):  
Escherichia Coli ◽  
Calcium Sulfate ◽  
Thermal Inactivation ◽  
Thermal Sensitivity ◽  
Ground Beef ◽  
Final Concentration ◽  
Escherichia Coli O157 ◽  
Frozen Ground ◽  
E Coli ◽  
D Values

Undercooked ground beef is a leading vehicle for acquiring Escherichia coli O157:H7 infections through consumption of foods. Studies have been performed to determine the effect of freezing and the combined effect of freezing and addition of a mixture of 20% acidic calcium sulfate (final concentration of 0.4% in ground beef) and 10% lactic acid (final concentration of 0.2% in ground beef) (ACS-LA) on the thermal sensitivity of E. coli O157:H7 in ground beef. Five strains of E. coli O157: H7 were separately inoculated into ground beef and held at 5°C for up to 10 days or −20°C for up to 3 weeks then heated at 57, 60, 62.8, 64.3, and 68.3°C to determine rates of thermal inactivation. Results revealed that D-values (decimal reduction times) at equivalent temperatures for four of five E. coli O157:H7 strains were less in the previously frozen than in the refrigerated ground beef and that strains isolated from ground beef in 1993 and 1994 were generally more sensitive to thermal inactivation than those isolated in 1999 and 2000. Only one strain of E. coli O157:H7 was used to determine the effect of ACS-LA in previously frozen or refrigerated ground beef on rates of thermal inactivation. The addition of ACS-LA to ground beef at 20 ml/kg increased the thermal sensitivity of E. coli O157:H7 in both previously frozen and refrigerated ground beef, with greatest rates of inactivation occurring in previously frozen ground beef containing ACS-LA. D-values at 57°C obtained for E. coli O157:H7 in previously refrigerated and frozen ground beef containing ACS-LA and ACS-LA diluted by half were significantly (P < 0.05) less than those obtained in ground beef with no ACS-LA added. D-values at 60 and 62.8°C were consistently less in ACS-LA treated ground beef, but for most treatments the results were not significantly (P > 0.05) different than the controls. Results revealed that the addition of ACS-LA to ground beef, whether frozen or refrigerated, can reduce the temperature or time required to kill E. coli O157:H7 during heating.

A Multiplex Polymerase Chain Reaction Assay for Rapid Detection and Identification of Escherichia coli O157:H7 in Foods and Bovine Feces†

2000 ◽  
Vol 63 (8) ◽  
pp. 1032-1037 ◽  
Author(s):  
PINA M. FRATAMICO ◽  
LORI K. BAGI ◽  
TIZIANA PEPE
Keyword(s):  
Escherichia Coli ◽  
Polymerase Chain Reaction ◽  
Multiplex Pcr ◽  
Multiplex Polymerase Chain Reaction ◽  
Ground Beef ◽  
Escherichia Coli O157 ◽  
Chain Reaction ◽  
E Coli ◽  
Polymerase Chain ◽  
Bovine Feces

A multiplex polymerase chain reaction (PCR) assay was designed to simplify detection of Escherichia coli O157:H7 and to identify the H serogroup and the type of Shiga toxin produced by this bacterium. Primers for a plasmid-encoded hemolysin gene (hly933), and chromosomal flagella (fliCh7; flagellar structural gene of H7 serogroup), Shiga toxins (stx1, stx2), and attaching and effacing (eaeA) genes were used in a multiplex PCR for coamplification of the corresponding DNA sequences from enterohemorrhagic E. coli (EHEC) O157:H7. Enrichment cultures of ground beef, blue cheese, mussels, alfalfa sprouts, and bovine feces, artificially inoculated with various levels of E. coli O157:H7 strain 933, were subjected to a simple DNA extraction step prior to the PCR, and the resulting amplification products were analyzed by agarose gel electrophoresis. Sensitivity of the assay was ≤1 CFU/g of food or bovine feces (initial inoculum level), and results could be obtained within 24 h. Similar detection levels were obtained with ground beef samples that underwent enrichment culturing immediately after inoculation and samples that were frozen or refrigerated prior to enrichment. The multiplex PCR facilitates detection of E. coli O157:H7 and can reduce the time required for confirmation of isolates by up to 3 to 4 days.

Thermal Inactivation of a Single Strain Each of Serotype O26:H11, O45:H2, O103:H2, O104:H4, O111:H−, O121:H19, O145:NM, and O157:H7 Cells of Shiga Toxin–Producing Escherichia coli in Wafers of Ground Beef†

2013 ◽  
Vol 76 (8) ◽  
pp. 1434-1437 ◽  
Author(s):  
J. B. LUCHANSKY ◽  
A. C. S. PORTO-FETT ◽  
B. A. SHOYER ◽  
J. PHILLIPS ◽  
D. EBLEN ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Shiga Toxin ◽  
Thermal Inactivation ◽  
Ground Beef ◽  
Sampling Time ◽  
Single Strain ◽  
E Coli ◽  
D Values ◽  
Cooking Times ◽  
Sterile Filter

For each of two trials, freshly ground beef of variable fat content (higher: 70:30 %lean:%fat; lower: 93:7 %lean:%fat) was separately inoculated with ca. 7.0 log CFU/g of a single strain of Escherichia coli serotypes O26:H11, O45:H2, O103:H2, O104:H4, O111:H−, O121:H19, O145:NM, and O157:H7. Next, ca. 3-g samples of inoculated beef were transferred into sterile filter bags and then flattened (ca. 1.0 mm thick) and vacuum sealed. For each temperature and sampling time, three bags of the inoculated wafers of beef were submerged in a thermostatically controlled water bath and heated to an internal temperature of 54.4°C (130°F) for up to 90 min, to 60°C (140°F) for up to 4 min, or to 65.6°C (150°F) for up to 0.26 min. In lower fat wafers, D-values ranged from 13.5 to 23.6 min, 0.6 to 1.2 min, and 0.05 to 0.08 min at 54.4, 60.0, and 65.6°C, respectively. Heating higher fat wafers to 54.4, 60.0, and 65.6°C generated D-values of 18.7 to 32.6, 0.7 to 1.1, and 0.05 to 0.2 min, respectively. In addition, we observed reductions of ca. 0.7 to 6.7 log CFU/g at 54.4°C after 90 min, ca. 1.1 to 6.1 log CFU/g at 60.0°C after 4 min, and 0.8 to 5.8 log CFU/g at 65.6°C after 0.26 min. Thus, cooking times and temperatures effective for inactivating a serotype O157:H7 strain of E. coli in ground beef were equally effective against the seven non-O157:H7 Shiga toxin–producing strains investigated herein.

Thermal Inactivation of Escherichia coli O157:H7 in Cow Manure Compost

2003 ◽  
Vol 66 (10) ◽  
pp. 1771-1777 ◽  
Author(s):  
XIUPING JIANG ◽  
JENNIE MORGAN ◽  
MICHAEL P. DOYLE
Keyword(s):  
Escherichia Coli ◽  
Green Fluorescent Protein ◽  
Thermal Inactivation ◽  
Fluorescent Protein ◽  
Escherichia Coli O157 ◽  
Cow Manure ◽  
E Coli ◽  
Manure Compost ◽  
D Values ◽  
Green Fluorescent

Rates of inactivation of a five-strain mixture of green fluorescent protein–labeled Escherichia coli O157:H7 in autoclaved and unautoclaved commercial cow manure compost with a moisture content of ca. 38% were determined at temperatures of 50, 55, 60, 65, and 70°C. Trypticase soy agar with ampicillin was determined to be the best medium for the enumeration of heat-injured and uninjured cells of green fluorescent protein–labeled E. coli O157:H7. The results obtained in this study revealed that in autoclaved compost, E. coli O157:H7 reductions of ca. 4 log CFU/g occurred within 8 h, 3 h, 15 min, 2 min, and <1 min at 50, 55, 60, 65, and 70°C, respectively. At 65 and 70°C, considerably less time was required to kill the pathogen in unautoclaved compost than in autoclaved compost. Decimal reduction times (D-values) for autoclaved compost at 50, 55, 60, 65, and 70°C were 137, 50.3, 4.1, 1.8, and 0.93 min, respectively, and D-values for unautoclaved compost at 50, 55, and 60°C were 135, 35.4, and 3.9 min, respectively. Considerable tailing was observed for inactivation curves, especially at 60, 65, and 70°C. These results are useful for identifying composting conditions that will reduce the risk of the transmission of E. coli O157:H7 to foods produced in the presence of animal fecal waste.

Thermal Inactivation of Escherichia coli O157:H7 in Beef Treated with Marination and Tenderization Ingredients

2008 ◽  
Vol 71 (7) ◽  
pp. 1349-1356 ◽  
Author(s):  
AVIK MUKHERJEE ◽  
YOHAN YOON ◽  
KEITH E. BELK ◽  
JOHN A. SCANGA ◽  
GARY C. SMITH ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Acetic Acid ◽  
Sodium Chloride ◽  
Thermal Inactivation ◽  
Ground Beef ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Log Reduction ◽  
Weight Losses ◽  
Beef Products

Internalization of Escherichia coli O157:H7 in nonintact beef products during mechanical tenderization or during injection of marination and tenderization ingredients is of concern if such products are undercooked. This study tested organic acids (0.2% citric acid and 0.3% acetic acid), potassium and calcium salts (1.8% potassium lactate, 0.63% calcium lactate, 0.86% calcium ascorbate, and 0.23% calcium chloride), and sodium chloride (2.5%) for their influence on thermal destruction of E. coli O157:H7 in ground beef serving as a model system. Ground beef batches (700 g; 5% fat) were mixed with equal volumes (22 ml) of each treatment solution or distilled water and portions (30 g) of treated ground beef were extruded in test tubes (2.5 by 10 cm). A five-strain mixture of E. coli O157:H7 (0.3 ml; 7 log CFU/g) was introduced at the center of the sample with a pipette. After overnight storage (4°C), simulating product marination, samples were heated to 60 or 65°C internal temperature, simulating rare and medium rare doneness of beef, in a circulating water bath. At 65°C, treatments with citric and acetic acid showed greater (P < 0.05) reduction (4 to 5 log CFU/g) of E. coli O157:H7 than all the other ingredients and the control (3 to 4 log CFU/g). Sodium chloride reduced weight losses (16 to 18% compared with 20 to 27% by citric or acetic acid) and resulted in a 4-log reduction in counts during cooking to 65°C. Ingredients such as citric or acetic acid may improve thermal inactivation of E. coli O157:H7 internalized in nonintact beef products, while sodium chloride may reduce cooking losses in such products.

Changes in Heat Resistance of Escherichia coli O157:H7 Following Heat Shock

1997 ◽  
Vol 60 (9) ◽  
pp. 1128-1131 ◽  
Author(s):  
NICOLE C. WILLIAMS ◽  
STEVEN C. INGHAM
Keyword(s):  
Escherichia Coli ◽  
Heat Shock ◽  
Heat Resistance ◽  
Ground Beef ◽  
Escherichia Coli O157 ◽  
Protective Effects ◽  
Cell Recovery ◽  
Short Term ◽  
E Coli ◽  
D Values

This study examined the effects of a heat shock at 45°C for 30 min on the subsequent heat resistance of Escherichia coli O157:H7 ATCC 43894 in Trypticase soy broth (TSB) and ground beef slurry (GBS). Cultures were grown to stationary phase, stored for 24 h at 4 to 6°C, and then heat shocked to simulate consumer mishandling of meat during the summer. Control or heat-shocked ATCC 43894 cells were then transferred to prewarmed TSB (54, 58, and 62°C) or GBS (58°C) and refrigerated TSB and GBS that were subsequently heated to and held at 58°C (TSB and GBS) and 62°C (TSB only). Heat shock increased D values by 37, 68, and 50% in 54, 58, and 62°C prewarmed TSB, respectively, but had no significant effect on the D value in 58°C GBS. Immediate plating of heated samples yielded greater cell recovery than if samples were held on ice prior to plating. Heat shock did not lead to significant increases in D values when cells were transferred to 4°C TSB and GBS that were heated to the test temperature. This study showed that for E. coli O157:H7 ATCC 43894 the heat-shock effect was lost upon subsequent chilling and rewarming and overshadowed by the protective effects of ground beef constituents. The results do not support the hypothesis that short-term temperature abuse will significantly increase the heat resistance of E. coli O157:H7 in ground beef.

Survival of Escherichia coli O157:H7 in Ground Beef after Sublethal Heat Shock and Subsequent Isothermal Cooking

2009 ◽  
Vol 72 (8) ◽  
pp. 1727-1731 ◽  
Author(s):  
K. M. WIEGAND ◽  
S. C. INGHAM ◽  
B. H. INGHAM
Keyword(s):  
Escherichia Coli ◽  
Heat Shock ◽  
Ground Beef ◽  
Shock Treatment ◽  
Escherichia Coli O157 ◽  
Heat Shock Treatment ◽  
E Coli ◽  
Cooking Process ◽  
Shock Temperature ◽  
D Values

Heat shock of Escherichia coli O157:H7 in broth media reportedly leads to enhanced survival during subsequent heating in broth medium or ground beef. Survival of E. coli O157:H7 during slow cooking thus may be enhanced by prior exposure to sublethal heat shock conditions, thereby jeopardizing the safety of slow-cooked products such as beef roasts. This study examined the effect of heat shocking E. coli O157:H7–inoculated lean (6 to 9% fat) ground beef on the survival of the pathogen in the same ground beef during a subsequent 4-h, 54.4°C cooking process. Six different combinations of heat shock temperature (47.2, 48.3, or 49.4°C) and time (5 or 30 min) were applied to a five-strain cocktail of microaerophilically grown cells in 25 g of prewarmed ground beef, which was followed by cooking at 54.4°C. Temperature during a 30-min heat shock treatment did not significantly affect E. coli O157:H7 survival during subsequent isothermal cooking (P > 0.05). Survival after a 5-min heat shock was higher when the heat shock temperature was 48.3 or 49.4°C (P < 0.05) than when it was 47.2°C. The D-values at 54.4°C (130°F) (D54.4-value) of the process significantly increased only when cells were exposed to a heat shock combination of 5 min at 49.4°C. Mean (n = 3 trials) reductions in E. coli O157:H7 during the 4-h, 54.4°C isothermal cooking process ranged from 4.3 to 7.5 log CFU/g. Heating E. coli O157:H7–contaminated beef at the high end of the sublethal temperature range for 5 min could increase survival of E. coli O157:H7 during subsequent slow-cooking processes.

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