Comparative Effect of Heat Shock on Survival of O157:H7 and Non-O157 Shiga Toxigenic Escherichia coli and Salmonella in Lean Beef with or without Moisture-Enhancing Ingredients.

Thermal tolerance of pathogenic bacteria has been shown to increase after exposure to sublethal elevated temperatures, or heat shock. We evaluated the effect of heat shock at 48°C on thermal tolerance (D55°C) of cocktails of O157 and non-O157 Shiga toxigenic Escherichia coli (STEC) and Salmonella in lean ground beef with or without moisture-enhancing ingredients. Beef was moisture enhanced to 110% (w) with a 5% NaCl-2.5% sodium tripolyphosphate (w/w) brine. Meat, with or without added brine, was inoculated (∼108 CFU/g) and heat shocked at 48°C for 0, 5, or 30 min, followed by isothermal heating at 55°C. Inoculated control samples were unenhanced and were not subject to heat shock. From the linear portion of the log CFU per gram surviving cells over time plots, D55°C-values (minutes) were calculated. D55°C was 20.43, 28.78, and 21.15 min for O157, non-O157, and Salmonella controls, respectively. Overall, heat shock significantly increased D55°C, regardless of pathogen (P < 0.05). After 30 min of heat shock, D55°C increased 89 and 160% for O157 STEC, 32 and 49% for non-O157 STEC, and 29 and 57% for Salmonella, in unenhanced and enhanced samples, respectively, relative to the pathogen control. D55°C for Salmonella was the same or significantly less than for O157 and non-O157 STEC, regardless of heat shock, and was significantly less than for O157 and non-O157 STEC in all trials with moisture-enhanced meat (P < 0.05). Moisture-enhancing ingredients significantly increased D55°C, regardless of pathogen (P < 0.05). We suggest that thermal processes validated against Salmonella may not prove effective against STEC in all cases and that regulators of the beef industry should focus attention on STEC in nonintact moisture-enhanced beef products.

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 $ 6.5-log CFU/g reduction of this pathogen in seasoned whole-muscle beef. Calculations based on D- and z-values obtained from isothermal ground beef studies increasingly overestimated destruction of E. coli O157:H7 in commercially cooked whole-muscle beef as process severity increased, with a regression line equation of observed reduction = 0.299 (predicted reduction) + 1.4373.

Identification of Escherichia coli O157:H7 surrogate organisms to evaluate beef carcass intervention treatment efficacy.

We compared the survival of potential pathogen surrogates-meat-hygiene indicators (non-Escherichia coli coliforms), biotype I E. coli, and lactic acid bacteria starter cultures-with survival of an E. coli O157:H7 (ECO157:H7) inoculum in beef carcass intervention trials. Survival of one lactic acid bacteria starter culture (Bactoferm LHP Dry [Pediococcus acidilactici and Pediococcus pentosaceus]), a five-isolate biotype I inoculum, and a five-isolate non-E. coli coliform inoculum, was compared with survival of a 12-isolate ECO157:H7 inoculum in interventions by using beef brisket (adipose and lean), cod fat membrane, or neck tissue. Treatments were grouped by abattoir size: small (6-day dry aging; 22°C acid treatment [2.5% acetic acid, 2% lactic acid, or Fresh Bloom], followed by 1-day dry aging; hot water) and large (warm acid treatment [5% acetic acid or 2% lactic acid] with or without a preceding hot water treatment). Reductions in pathogen and surrogate inocula were determined with excision sampling. A surrogate was considered a suitable replacement for ECO157:H7 if the intervention produced a reduction in surrogate levels that was not significantly greater (P≥0.05) than that observed for ECO157:H7. All three surrogate inocula were suitable as ECO157 surrogates for dry aging and acid spray plus dry-aging treatments used by small abattoirs. No one inoculum was suitable as an ECO157 surrogate across all intervention treatments used by large abattoirs. Effects seen on neck tissue were representative of other tissues, and the low value of the neck supports its use as the location for evaluating treatment efficacy in in-plant trials. Results support using nonpathogenic surrogate organisms to validate beef carcass intervention efficacy.

Predicting growth-no growth of Listeria monocytogenes on vacuum-packaged ready-to-eat meats.

Compliance with U.S. Department of Agriculture (USDA) composition-based labeling standards often has been regarded as evidence of the shelf stability of ready-to-eat (RTE) meats. However, the USDA now requires further proof of shelf stability. Our previous work included development of equations for predicting the probability of Staphylococcus aureus growth based on the pH and a(w) of an RTE product. In the present study, we evaluated the growth-no-growth during 21 degrees C storage of Listeria monocytogenes on 39 vacuum-packaged commercial RTE meat products with a wide range of pH (4.6 to 6.5), a(w) (0.47 to 0.98), and percent water-phase salt (%WPS; 2.9 to 34.0). Pieces of each product were inoculated with a five-strain cocktail of L. monocytogenes and vacuum packaged, and L. monocytogenes levels were determined immediately after inoculation and after storage at 21 degrees C for up to 5 weeks. L. monocytogenes grew on 13 of 14 products labeled "keep refrigerated" but not on any of the 25 products sold as shelf stable. Using bias reduction logistic regression data analysis, the probability of L. monocytogenes growth (Pr) could be predicted as a function of pH and a(w): Pr = exp[-59.58 + (4.67 x pH) + (35.05 x a(w))]/{1 + exp[-59.58 + (4.67 x pH) + (35.05 x a(w))]}. Pr also could be predicted as a function of pH and %WPS: Pr = exp[-20.52 + (4.10 x pH) - (0.51 x %WPS)]/{1 + exp[-20.52 + (4.10 x pH) - (0.51 x %WPS)]}. The equations accurately predicted L. monocytogenes growth (Pr values of 0.68 to 0.99) or no growth (Pr values of <0.01 to 0.26) and with our equations for predicting S. aureus growth will be useful for evaluating RTE meat shelf stability.

Destruction of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus achieved during manufacture of whole-muscle beef Jerkyin home-style dehydrators.

Adequate lethality in jerky manufacture destroys appropriate levels of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus. Our goal was to evaluate the lethality of four home-style dehydrator processes against these pathogens. Whole-muscle beef strips were inoculated with L. monocytogenes (five strains), S. aureus (five strains), or a mixed inoculum of E. coli O157:H7 (five strains) and Salmonella (eight strains). After allowing for attachment, strips were marinated in Colorado-, Original-, or Teriyaki-seasoned marinade for 22 to 24 h and dried in three home-style dehydrators (Garden Master, Excalibur, and Jerky Xpress) at 57.2 to 68.3°C. Samples were taken postmarination; after 4, 6, and 8 h of drying; and after drying, followed by heating for 10 min in a 135°C oven. Surviving inocula were enumerated. With a criterion of ≥ 5.0-log CFU/cm² reduction as the standard for adequate process lethality, none of the samples achieved the target lethality for any pathogen after 4 h of drying, even though all samples appeared "done" (water activity of less than 0.85). A postdehydration oven-heating step increased the proportion of samples meeting the target lethality after 4 h of drying to 71.9, 88.9, 55.6, and 77.8% for L. monocytogenes-, S. aureus-, E. coli O157:H7-, and Salmonella-inoculated samples, respectively, and after an 8-h drying to 90.6, 94.4, 83.3, and 91.7% of samples, respectively. Significantly greater lethality was seen with higher dehydrator temperature and significantly lower with Teriyaki-marinated samples. Heating jerky dried in a home-style dehydrator for 10 min in a 135°C oven would be an effective way to help ensure safety of this product.

Predicting behavior of Staphylococcus aureus, salmonella serovars, and Escherichia coli O157: H7 in pork products during single and repeated temperature abuse periods.

Tools for predicting growth of Staphylococcus aureus, Salmonella, and Escherichia coli O157:H7 (THERM; temperature history evaluation for raw meats) have been developed using ground pork and sausage. THERM tools have been tested with three types of pork sausage but not with other pork products or during sequential temperature abuse periods. We conducted inoculation studies (five strains each of S. aureus and/or Salmonella plus E. coli O157:H7) with simulated cooling of warm sausages, inprocess warming of bratwurst, isothermal temperature abuse of pork frankfurter batter, and two sequential periods of 13, 15.6, or 21.1 degrees C temperature abuse of breakfast sausage, natural (additive-free) chops, and enhanced (phosphate solution-injected) loins. In sequential temperature abuse studies, a temperature abuse period (> or =24 h) occurred before and after either refrigeration (5 degrees C for 24 h), or freezing (-20 degrees C for 24 h) and thawing (24 h at 5 degrees C). Pathogen growth predictions from THERM developed using ground pork and sausage were compared with experimental results of 0 to 3.0 log CFU of growth. Across all temperature abuse conditions, qualitative predictions (growth versus no growth) made using the pork tool (n = 133) and the sausage tool (n = 115) were accurate (51 and 50%, respectively), fail-safe (44 and 50%), or fail-dangerous (5 and 0%). Quantitative predictions from the two tools were accurate (29 and 22% , respectively), fail-safe (59 and 73%), or fail-dangerous (12 and 5%). Pathogen growth was greater during the second sequential temperature abuse period but not significantly so (P > 0.05). Both THERM tools provide useful qualitative predictions of pathogen growth in pork products during isolated or sequential temperature abuse events.

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.

Validation of ground-and-formed beef jerky processes using commercial lactic acid bacteria starter cultures as pathogen surrogates.

Beef jerky has been linked to multiple outbreaks of salmonellosis and Escherichia coli O157:H7 infection over the past 40 years. With increasing government scrutiny of jerky-making process lethality, a simple method by which processors can easily validate the lethality of their ground-and-formed beef jerky process against Salmonella' and E. coli O157:H7 is greatly needed. Previous research with whole-muscle beef jerky indicated that commercial lactic acid bacteria (LAB) may be more heat resistant than Salmonella and E. coli O157:H7, suggesting the potential use of LAB as pathogen surrogates. Of six commercial LAB-containing cultures evaluated for heat resistance in ground-and-formed beef jerky, Saga 200 (Pediococcus spp.) and Biosource (Pediococcus acidilactici) were identified as consistently more heat resistant than Salmonella and E. coli O157:H7. Six representative ground-and-formed beef jerky commercial processes, differing widely in lethality, were used to identify an appropriate level of LAB reduction that would consistently indicate a process sufficiently lethal (> or = 5.0-log reduction) for Salmonella and E. coli O157:H7. Both Saga 200 and Biosource consistently predicted adequate process lethality with a criterion of > or = 5.0-1og reduction of LAB. When either LAB decreased by > or = 5.0 log CFU, processes were sufficiently lethal against Salmonella and E. coli O157:H7 in 100% of samples (n=39 and 40, respectively). Use of LAB as pathogen surrogates for ground-and-formed beef jerky process validation was fieldtested by three small meat processors, who found this technique easy to use for process validation.

Predicting growth-no growth of Staphylococcus aureus on vacuum-packaged ready-to-eat meats.

U.S. Department of Agriculture (USDA) composition-based labeling standards for various ready-to-eat (RTE) meat products typically specify maximum product pH and/or moisture:protein ratio and less often maximum water activity (a(w)). Compliance with these standards often has been regarded as proof of shelf stability. However, the USDA now requires additional proof, e.g., challenge study results, of shelf stability. The pathogen most likely to grow on vacuum-packaged, reduced-moisture products is Staphylococcus aureus. Therefore, vacuum-packaged RTE products that do not support S. aureus growth at room temperature could be considered shelf stable. We developed mathematical equations for predicting whether S. aureus would grow under such conditions. Twenty-four commercial RTE meat products and 10 intentionally misprocessed products (insufficient drying, fermentation, and/or salt) were inoculated with a five-strain cocktail of S. aureus, vacuum packaged, and stored at 21 degrees C. Initial, 7-day, and 28-day S. aureus counts were recorded. Product pH, a(w), moisture:protein ratio, and percentage of water-phase salt (%WPS) also were determined. S. aureus grew only in the intentionally misprocessed products and in some commercial products labeled "keep refrigerated." Using bias reduction logistic regression data analysis, the probability of S. aureus growth (Pr) could be predicted by either of two equations. The first was based on pH and a(w) values: Pr = exp[-59.36 + (5.75 x pH) + (28.73 x a(w))]/{1 + [exp(-59.36 + (5.75 x pH) + (28.73 x a(w))]}. The second was based on pH and %WPS: Pr = exp[-26.93 + (5.38 x pH) + (-0.61 x %WPS)]/{1 + exp[-26.93 + (5.38 x pH) + (-0.61 x %WPS)]}. These equations accounted for observed S. aureus growth-no growth results and will be a useful tool for evaluating the shelf stability of RTE meats.

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.

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.

Manual squeezing as an alternative to mechanical stomaching in preparing beef carcass sponge samples for microbiological analysis.

The U.S. Department of Agriculture (USDA) requires beef abattoir operators to periodically analyze beef carcass sponge samples for levels of Escherichia coli. Additional beef carcass sponge sampling is commonly used by processors to evaluate the efficacy of beef abattoir antimicrobial intervention systems. The USDA sample preparation procedure requires that beef carcass sponge samples be mechanically stomached for 2 min before the sample fluid is squeezed out for analysis. When a large number of sponge samples must be analyzed, the stomaching step can limit throughput. In this study, we compared the USDA sample preparation procedure with repeatedly squeezing the sponge during a 10-s interval to expel the sample fluid. Separate sponge samples were obtained from each half of 100 chilled postintervention beef carcasses from a large-volume abattoir during a 4-month period. The USDA and squeezing treatments were randomly assigned to the halves of each carcass. All sponge samples were analyzed for E. coli, coliforms, Enterobacteriaceae, and aerobic mesophilic bacteria using Petrifilm methods. The sample preparation method had no significant effect (signed rank value > 0.05) on the results of any analytical test, although aerobic mesophilic bacteria counts tended to be higher after the USDA method than after manual squeezing alone. These results suggest that manual squeezing may be a simple and rapid alternative sample preparation method when gram-negative bacteria such as E. coli, coliforms, or Enterobacteriaceae are being enumerated from beef carcass sponge samples used to monitor operational abattoir hygiene.

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.

Modeling the survival of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium during fermentation, drying, and storage of soudjouk-style fermented sausage.

This study quantified and modeled the survival of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Typhimurium in soudjouk-style fermented sausage during fermentation, drying, and storage. Batter prepared from ground beef (20% fat), seasonings, starter culture, and dextrose was separately inoculated with a multi-strain mixture of each pathogen to an initial inoculum of ca. 6.5 log(10) CFU/g in the batter. The sausages were subsequently fermented at 24 degrees C with a relative humidity (RH) of 90% to 95% for 3 to 5 days to ca. pH 5.2, pH 4.9 or pH 4.6, then dried at 22 degrees C to a(w) 0.92, a(w) 0.89, or a(w) 0.86, respectively, and then stored at 4, 21, or 30 degrees C for up to 60 days. Lethality of the three pathogens was modeled as a function of pH, a(w) and/or storage temperature. During fermentation to pH 5.2 to pH 4.6, cell reductions ranged from 0 to 0.9 log(10) CFU/g for E. coli O157:H7, 0.1 to 0.5 log(10) CFU/g for L. monocytogenes, and 0 to 2.2 log(10) CFU/g for S. Typhimurium. Subsequent drying of sausages of pH 5.2 to pH 4.6 at 22 degrees C with 80% to 85% RH for 3 to 7 days to a(w) of 0.92 to a(w) 0.86 resulted in additional reductions that ranged from 0 to 3.5 log(10) CFU/g for E. coli O157:H7, 0 to 0.4 log(10) CFU/g for L. monocytogenes, and 0.3 to 2.4 log(10) CFU/g for S. Typhimurium. During storage at 4, 21, or 30 degrees C the reduction rates of the three pathogens were generally higher (p<0.05) in sausages with lower pH and lower a(w) that were stored at higher temperatures. Polynomial equations were developed to describe the inactivation of the three pathogens during fermentation, drying, and storage. The applicability of the resulting models for fermented sausage was evaluated by comparing model predictions with published data. Pathogen reductions estimated by the models for E. coli O157:H7 and S. Typhimurium were comparable to 67% and 73% of published data, respectively. Due to limited published data for L. monocytogenes, the models for L. monocytogenes would need additional validations. Results of pathogen reductions from this study may be used as a reference to assist manufacturers of soudjouk-style sausages to adopt manufacturing processes that meet the regulatory requirements. The resulting models may also be used for estimating the survival of E. coli O157:H7 and S. Typhimurium in other similar fermented sausage during fermentation and storage.

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.

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.

Using predictive microbiology to evaluate risk and reduce economic losses associated with raw meats and poultry exposed to temperature abuse.

The Department of Defense suffers economic losses when temperature-abused raw meat and poultry are condemned. Current US Army guidance regarding time/temperature limits associated with these foods (RISK-3 category) is ultraconservative, especially at lower temperatures. We have developed a more accurate, yet conservative or "fail-safe" computer-based tool for predicting pathogen growth in raw meat and poultry. In 20 trials of this tool, growth (> 0.3 log colony-forming unit increase) or no growth of Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus was accurately predicted 67% to 95% of the time for inoculated and temperature-abused poultry products and ground beef. Fail-safe predictions were obtained in trials for which the tool was inaccurate. The predictive tool is ready for further validation trials and field testing. Using this tool as a supplement to the current guidance will decrease losses associated with the condemnation of raw meat and poultry products exposed to short-term temperature abuse.

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.

Survival of Staphylococcus aureus and Listeria monocytogenes on vacuum-packaged beef jerky and related products stored at 21 degrees C.

In the manufacture of beef jerky, a thermal lethality step is followed by drying to prevent growth of pathogenic bacterial postprocessing contaminants on the finished product. Recent guidelines from the U.S. Department of Agriculture have raised the question of the maximum water activity (a(w)) in jerky products that will inhibit growth of pathogenic bacteria. The survival of the potential postprocessing contaminants Staphylococcus aureus and Listeria monocytogenes was evaluated on 15 vacuum-packaged beef jerky and related products with a(w) values ranging from 0.47 to 0.87, just below the 0.88 limit reported for anaerobic growth of S. aureus. Small individual product pieces were inoculated on the outer surface with five strains each of S. aureus and L. monocytogenes, repackaged under vacuum, and stored at room temperature (21 degrees C) for 4 weeks. Pathogen numbers were determined before storage and after 1 and 4 weeks. None of the 15 jerky products supported growth of either pathogen. Counts of S. aureus fell by 0.2 to 1.8 log CFU after 1 week of storage and by 0.6 to 5.3 log CFU after 4 weeks of storage. Numbers of L. monocytogenes fell by 0.6 to 4.7 log CFU and by 2.3 to 5.6 log CFU after 1 and 4 weeks of storage, respectively. Although factors other than a(w) may have some effect on pathogen survival, the results of the present study clearly support drying beef jerky to an a(w) of < or = 0.87 to ensure that bacterial pathogens cannot grow on vacuum-packaged product stored at room temperature.

Survival of Streptococcus pyogenes on foods and food contact surfaces.

Streptococcus pyogenes causes septic sore throat in millions of Americans each year and may be transmitted from food handlers to food contact surfaces, foods, and consumers. This study examined the individual survival of six S. pyogenes strains on food contact surfaces (plastic and ceramic plates, plastic cups, and stainless steel utensils) held at 21 degrees C for 2 h and on tomatoes stored aerobically at 21 degrees C for 2 h and at 5 degrees C for 24 h. Survival of a cocktail of the six S. pyogenes strains was also evaluated on vacuum-packaged ready-to-eat meats and cheeses held at 21 degrees C for 8 h and at 5 degrees C for 24 h. Populations generally did not change on tomatoes, cheeses, or beef bologna; however, there were small (0.1 to 0.7 log CFU) but statistically significant decreases (P < 0.05) in average S. pyogenes populations on turkey luncheon meat and beef summer sausage stored for 8 h at 21degrees C and on beef summer sausage stored for 24 h at 5 degrees C. On food contact surfaces, average populations either decreased slightly (P > or = 0.05) or remained constant, with the exception of three strains that significantly decreased in number on ceramic plates (P < 0.05; average decreases, 0.3 log CFU). Results of this study suggest the importance of preventing the contamination of foods and food contact surfaces with S. pyogenes by infected workers.