Steven C. Ingham

Predicting Pathogen Growth during Short-Term Temperature Abuse of Raw Pork, Beef, and Poultry Products: Use of an Isothermal-Based Predictive Tool

A computer-based tool (available at: www.wisc.edu/foodsafety/meatresearch) was developed for predicting pathogen growth in raw pork, beef, and poultry meat. The tool, THERM (temperature history evaluation for raw meats), predicts the growth of pathogens in pork and beef (Escherichia coli O157:H7, Salmonella serovars, and Staphylococcus aureus) and on poultry (Salmonella serovars and S. aureus) during short-term temperature abuse. The model was developed as follows: 25-g samples of raw ground pork, beef, and turkey were inoculated with a five-strain cocktail of the target pathogen(s) and held at isothermal temperatures from 10 to 43.3 degrees C. Log CFU per sample data were obtained for each pathogen and used to determine lag-phase duration (LPD) and growth rate (GR) by DMFit software. The LPD and GR were used to develop the THERM predictive tool, into which chronological time and temperature data for raw meat processing and storage are entered. The THERM tool then predicts a delta log CFU value for the desired pathogen-product combination. The accuracy of THERM was tested in 20 different inoculation experiments that involved multiple products (coarse-ground beef, skinless chicken breast meat, turkey scapula meat, and ground turkey) and temperature-abuse scenarios. With the time-temperature data from each experiment, THERM accurately predicted the pathogen growth and no growth (with growth defined as delta log CFU > 0.3) in 67, 85, and 95% of the experiments with E. coli 0157:H7, Salmonella serovars, and S. aureus, respectively, and yielded fail-safe predictions in the remaining experiments. We conclude that THERM is a useful tool for qualitatively predicting pathogen behavior (growth and no growth) in raw meats. Potential applications include evaluating process deviations and critical limits under the HACCP (hazard analysis critical control point) system.

Lethality of Commercial Whole-Muscle Beef Jerky Manufacturing Processes against Salmonella Serovars and Escherichia coli O157:H7

Thermal processes used in making whole-muscle beef jerky include a drying step, which may result in enhanced pathogen thermotolerance and evaporative cooling that reduce process lethality. Several salmonellosis outbreaks have been associated with beef jerky. In this study, a standardized process was used to inoculate beef strips with five-strain cocktails of either Salmonella serovars or Escherichia coli O157:H7, to marinate the strips at pH 5.3 for 22 to 24 h at 5 degrees C, and to convert the strips to jerky using various heating and drying regimes. Numbers of surviving organisms were determined during and after heating and drying. Salmonella reductions of > or = 6.4 log CFU and similar reductions in E. coli O157:H7 were best achieved by ensuring that high wet-bulb temperatures were reached and maintained early in the process (51.7 or 54.4 degrees C for 60 min, 57.2 degrees C for 30 min, or 60 degrees C for 10 min) followed by drying at 76.7 degrees C (dry-bulb temperature). Processes with less lethality that reduced counts of both pathogens by > or = 5.0 log CFU were (i) heating and drying at 76.7 degrees C (dry bulb) within 90 min of beginning the process, (ii) heating for successive hourly intervals at 48.9, 54.4, 60, and 76.7 degrees C (dry bulb), and (iii) heating at 51.7 degrees C (dry bulb) and then drying at 76.7 degrees C (dry bulb), starting before the product water activity dropped below 0.86. In several trials, separate beef strips were inoculated with a commercial Pediococcus acidilactici starter culture as a potential surrogate for evaluating pathogen thermotolerance. The results of these trials suggested that this experimental approach may be useful for in-plant validation of process lethality.

Using Indicator Bacteria and Salmonella Test Results from Three Large-Scale Beef Abattoirs over an 18-Month Period To Evaluate Intervention System Efficacy and Plan Carcass Testing for Salmonella

To develop a process for predicting the likelihood of Salmonella contamination on beef carcasses, we evaluated the influence of several possible causative factors (i.e., year, abattoir, day of week, month, and intervention system components) on the risk of Salmonella and indicator organism contamination. Hide and carcass sponge samples were collected in 2005 to 2006 in six steps at three abattoirs in the East (A), Midwest (B), and Southwest (C) United States. Each abattoir used the same intervention system. Samples were analyzed for aerobic plate counts (APCs; n = 18,990) and Enterobacteriaceae counts (EBCs; n = 18,989) and the presence or absence of Salmonella (n = 5,355). Our results demonstrated that many factors play a significant role in the level of microbial contamination of beef carcasses. Overall, Salmonella prevalence and EBC levels were significantly higher in 2006 than in 2005. APCs and EBCs were highest in abattoirs A (3.57 log CFU/100 cm2) and B (1.31 log CFU/100 cm2). The odds of detecting a positive Salmonella isolate were greatest in abattoir C and lowest in abattoir A. Across the three abattoirs, the overall intervention process effectively reduced microbiological contamination. Salmonella prevalence fell from 45% (preevisceration) to 0.47% (postchilled-lactic acid), and there were APC and EBC reductions of 5.43 and 5.28 log CFU/100 cm2, respectively, from hide-on to postchilled-lactic acid samples. At each abattoir, composites of three individual EBC-negative carcass samples yielded Salmonella-negative results 97 to 99% of the time. These results suggest the possibility of using indicator test results to accurately predict the absence of Salmonella in a beef carcass sample.

Lethality of home-style dehydrator processes against Escherichia coli O157:H7 and salmonella serovars in the manufacture of ground-and-formed beef jerky and the potential for using a pathogen surrogate in process validation.

Ground-and-formed beef jerky can be made easily at home with ground beef and kits that include spice, cure, and jerky-forming equipment. Ground beef poses inherent risks of illness due to Escherichia coli O157:H7 and Salmonella contamination, making adequate pathogen lethality important in jerky manufacturing. We evaluated the effectiveness of drying regimes at eliminating E. coli O157:H7 and Salmonella in seasoned ground-and-formed beef jerky manufactured with three home-style dehydrators and one small commercial unit. Inoculated jerky strips were dried for up to 12 or 24 h in a home-style or the commercial unit, respectively, with target drying temperatures ranging from 51.7 degrees C (125 degrees F) to 71.1 degrees C (160 degrees F). Pathogen lethality varied with seasoning, temperature, and drying time (n = 288 samples). Lethality against E. coli O157:H7 ranged from 1.5 log CFU (Jerky Xpress, 57.2 degrees C [135 degrees F], 4 h) to 6.4 log CFU (Gardenmaster, 68.3 degrees C [155 degrees F], 12 h), and varied with seasoning. Lethality against Salmonella ranged from 1.7 log CFU (Jerky Xpress, 57.2 degrees C [135 degrees F], 4 h) to 6.0 log CFU (Gardenmaster, 68.3 degrees C [155 degrees F], 12 h), and also varied with seasoning. There was a > or =5-log CFU reduction in both pathogens in 0, 10, and 27 % of samples at 4, 8, and 12 h, respectively. Heating jerky for 10 min at 135 degrees C (275 degrees F) 4 or 6 h postdrying increased lethality, on average, 2.99 log CFU for Salmonella and 3.02 log CFU for E. coli O157:H7. The use of a lactic acid bacterium culture (Pediococcus spp.) as a pathogen surrogate accurately predicted safety in 28 % of samples containing E. coli O157:H7 and 78% of Salmonella-inoculated samples.

Evaluation of potential for inhibition of growth of Escherichia coli O157:H7 and multidrug-resistant Salmonella serovars in raw beef by addition of a presumptive Lactobacillus sakei ground beef isolate.

The efficacy of adding presumptive Lactobacillus sakei (LS) strain 10-EGR-a, the most inhibitory from among 12 ground beef Lactobacillus isolates, to inhibit growth by Escherichia coli O157:H7 and multidrug-resistant (MDR) Salmonella (serovars Newport and Typhimurium) was evaluated in a beef-derived broth medium at 10 degrees C and in fresh raw ground beef at 10 and 5 degrees C. Pathogen inhibition was observed in the broth medium at both high (10(8):10(5) to 10(7):10(5)) and low (10(6):10(5) to 10(5):10(5)) LS:pathogen ratios. After 9 days at 10 degrees C, in broth medium with high LS:pathogen ratios, growth of E. coli O157:H7 and MDR Salmonella was inhibited by an average of 2.6 and 3.2 log CFU/ml, respectively, whereas in broth medium with low LS:pathogen ratios, E. coli O157:H7 and MDR Salmonella growth was inhibited by an average of 2.8 and 1.8 log CFU/ml, respectively. However, in raw ground beef no significant inhibition was seen with LS:pathogen ratios of 10(5):10(2) to 10(5):10(3). Significant inhibition was seen at very high LS:pathogen ratios (10(6) to 10(7):10(2) to 10(3)), but gross spoilage of the product occurred by day 6. Although presumptive LS 10-EGR-a can inhibit growth of E. coli O157:H7 and MDR Salmonella in a beef-derived broth medium, the inability to produce similar results in ground beef without deleteriously affecting the quality of the product is a limitation that needs further investigation.

Survival of Escherichia coli O157:H7 in ground beef after sublethal heat shock and subsequent isothermal cooking.

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 degrees C cooking process. Six different combinations of heat shock temperature (47.2, 48.3, or 49.4 degrees 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 degrees 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 degrees C (P < 0.05) than when it was 47.2 degrees C. The D-values at 54.4 degrees C (130 degrees 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 degrees C. Mean (n = 3 trials) reductions in E. coli O157:H7 during the 4-h, 54.4 degrees 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.

Mathematical Approaches To Estimating Lag-Phase Duration and Growth Rate for Predicting Growth of Salmonella Serovars, Escherichia coli O157:H7, and Staphylococcus aureus in Raw Beef, Bratwurst, and Poultry

This study was done to optimize accuracy of predicting growth of Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus in temperature-abused raw beef, poultry, and bratwurst (with salt but without added nitrite). Four mathematical approaches were used with experimentally determined lag-phase duration (LPD) and growth rate (GR) values to develop 12 versions of THERM (Temperature History Evaluation for Raw Meats; http://www.meathaccp.wisc.edu/ THERM/calc.aspx), a computer-based tool that calculates elapsing lag phase or growth that occurs in each entered time interval and sums the results of all intervals to predict growth. Each THERM version utilized LPD values calculated by linear interpolation, quadratic equation, piecewise linear regression, or exponential decay curve and GR values calculated by linear interpolation, quadratic equation, or piecewise linear regression. Each combination of mathematical approaches for LPD and GR calculations was defined as another THERM version. Time, temperature, and pathogen level (log CFU per gram) data were obtained from 26 inoculation experiments with ground beef, pork sausages, and poultry. Time and temperature data were entered into the 12 THERM versions to obtain pathogen growth. Predicted and experimental results were qualitatively described and compared (growth defined as > 0.3-log increase) or quantitatively compared. The 12 THERM versions had qualitative accuracies of 81.4 to 88.6% across 70 combinations of product, pathogen, and experiment. Quantitative accuracies within +/-0.3 log CFU were obtained for 51.4 to 67.2% of the experimental combinations; 82.9 to 88.6% of the quantitative predictions were accurate or fail-safe. Piecewise linear regression or linear interpolation for calculating LPD and GR yielded the most accurate THERM performance.

Use of Enterobacteriaceae Analysis Results for Predicting Absence of Salmonella Serovars on Beef Carcasses

Previous work using a large data set (no. 1, n = 5355) of carcass sponge samples from three large-volume beef abattoirs highlighted the potential use of binary (present or absent) Enterobacteriaceae results for predicting the absence of Salmonella on carcasses. Specifically, the absence of Enterobacteriaceae was associated with the absence of Salmonella. We tested the accuracy of this predictive approach by using another large data set (no. 2, n = 2,163 carcasses sampled before or after interventions) from the same three data set no. 1 abattoirs over a later 7-month period. Similarly, the predictive approach was tested on smaller subsets from data set no. 2 (n = 1,087, and n = 405) and on a much smaller data set (no. 3, n = 100 postintervention carcasses) collected at a small-volume abattoir over 4 months. Of Enterobacteriaceae-negative data set no. 2 carcasses, > 98% were Salmonella negative. Similarly accurate predictions were obtained in the two data subsets obtained from data set no. 2 and in data set no. 3. Of final postintervention carcass samples in data set nos. 2 and 3, 9 and 70%, respectively, were Enterobacteriaceae positive; mean Enterobacteriaceae values for the two data sets were -0.375, and 0.169 log CFU/100 cm2 (detection limit = -0.204, and Enterobacteriaceae negative assigned a value of -0.505 log CFU/100 cm2). Salmonella contamination rates for final postintervention beef carcasses in data set nos. 2 and 3 were 1.1 and 7.0%, respectively. Binary Enterobacteriaceae results may be useful in evaluating beef abattoir hygiene and intervention treatment efficacy.

Predicting pathogen growth during short-term temperature abuse of raw sausage.

Lag-phase duration (LPD) and growth rate (GR) values were calculated from experimental data obtained using a previously described protocol (S. C. Ingham, M. A. Fanslau, G. M. Burnham, B. H. Ingham, J. P. Norback, and D. W. Schaffner, J. Food Prot. 70:1445-1456, 2007). These values were used to develop an interval accumulation-based tool designated THERM (temperature history evaluation for raw meats) for predicting growth or no growth of Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus in temperature-abused raw sausage. Data (time-temperature and pathogen log CFU per gram) were obtained from six inoculation experiments with Salmonella, E. coli O157:H7, and S. aureus in three raw pork sausage products stored under different temperature abuse conditions. The time-temperature history from each experiment was entered into THERM to predict pathogen growth. Predicted and experimental results were described as growth (> 0.3 log increase in CFU) or no growth (< or = 0.3 log increase in CFU) and compared. The THERM tool accurately predicted growth or no growth for all 18 pathogen-experiment combinations. When compared with the observed changes in log CFU values for the nine pathogen-experiment combinations in which pathogens grew, the predicted changes in log CFU values were within 0.3 log CFU for three combinations, exceeded observed values by 0.4 to 1.5 log CFU in four combinations, and were 1.2 to 1.4 log CFU lower in two combinations. The THERM tool approach appears to be useful for predicting pathogen growth versus no growth in raw sausage during temperature abuse, although further development and testing are warranted.

Evaluating lethality of beef roast cooking treatments against Escherichia coli O157:H7.

Added salt, seasonings, and phosphates, along with slow- and/or low-temperature cooking impart desirable characteristics to whole-muscle beef, but might enhance Escherichia coli O157:H7 survival. We investigated the effects of added salt, seasoning, and phosphates on E. coli O157:H7 thermotolerance in ground beef, compared E. coli O157:H7 thermotolerance in seasoned roasts and ground beef, and evaluated ground beef-derived D- and z-values for predicting destruction of E. coli O157:H7 in whole-muscle beef cooking. Inoculated seasoned and unseasoned ground beef was heated at constant temperatures of 54.4, 60.0, and 65.5°C to determine D- and z-values, and E. coli O157:H7 survival was monitored in seasoned ground beef during simulated slow cooking. Inoculated, seasoned whole-muscle beef roasts were slow cooked in a commercial smokehouse, and experimentally determined lethality was compared with predicted process lethality. Adding 5% seasoning significantly decreased E. coli O157:H7 thermotolerance in ground beef at 54.4°C, but not at 60 or 65.5°C. Under nonisothermal conditions, E. coli O157:H7 thermotolerance was greater in seasoned whole-muscle beef than in seasoned ground beef. Meeting U.S. Government (U.S. Department of Agriculture, Food Safety and Inspection Service, 1999, Appendix A) whole-muscle beef cooking guidance, which targets Salmonella destruction, would not ensure ≥6.5-log CFU/g reduction of E. coli O157:H7 in ground beef systems, but generally ensured