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.

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.

Evaluating microbial safety of slow partial-cooking processes for bacon: use of a predictive tool based on small-scale isothermal meat inoculation studies.

The objective of this study was to develop a predictive tool for evaluating the safety of slow cooking of pork products and identifying associated critical limits. Small-scale (25 g) ground pork isothermal inoculation studies were done to determine Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus estimated critical times (time until growth reached a predefined increase of concern). Estimated critical time values ranged from 720 min at 21 degrees C (S. aureus) to 120 min at 40.6 degrees C (E. coli O157:H7) and were used to develop a multiple-temperature-interval predictive tool for non-isothermal processes. To test predictions, cured-pumped pork bellies were inoculated with Salmonella serovars, E. coli O157:H7, and S. aureus, subjected to slow partial cooking, and quantitatively analyzed for pathogens. Processes lasted 6 to 18 h, with the product interior temperature within the 21 to 46 degrees C range for 263 to 1080 min (high-humidity processes) and 217 to 921 min (low-humidity processes). Growth of Salmonella serovars (>0.3 log), E. coli O157:H7 (>0.3 log), and S. aureus (>1.3 log) in the pork belly interior was predicted for 10, 14, and 5 of 18 trials, respectively. The tool was fail-safe, because pathogen growth, relative to time zero, did not occur anytime regardless of whether it was predicted. For the pork belly surface, the tool performed similarly. Estimated critical time values obtained by fitting the Baranyi equation to isothermal experiment data were also determined and, if used in the predictive tool, would result in even more conservative predictions. Our study substantiates the safety of the tested bacon slow partial-cooking processes and the potential usefulness of our isothermal-based tool in process safety evaluation.

Evaluation of small-scale hot-water postpackaging pasteurization treatments for destruction of Listeria monocytogenes on ready-to-eat beef snack sticks and natural-casing wieners.

This study was conducted to evaluate small-scale hot-water postpackaging pasteurization (PPP) as a postlethality (post-cooking) treatment for Listeria monocytogenes on ready-to-eat beef snack sticks and natural-casing wieners. Using a commercially available plastic packaging film specifically designed for PPP applications and 2.8 liters of boiling water (100 degrees C) in a sauce pan on a hot plate, an average reduction in L. monocytogenes numbers of > or = 2 log units was obtained using heating times of 1.0 min for individually packaged beef snack sticks (three brands) and 4.0 min for packages of four sticks (two brands) and seven sticks (three brands). Average product surface temperatures, measured as soon as possible after PPP and opening the package, were 47 to 51.5, 58 to 61.5, and 58.5 to 61 degrees C for the beef snack sticks packages of one, four, and seven sticks per package, respectively. A treatment of 7.0 min for packages of four natural-casing wieners (three brands) achieved L. monocytogenes reductions of > or = 1.0 log unit and average product surface temperature of 60.5 to 63.5 degrees C. Cooked-out fat and moisture resulting from tested treatments ranged from 0.2 to 1.1% by weight for beef snack sticks and from 0.4 to 1.2% by weight for natural-casing wieners. For natural-casing wieners, PPP had no detrimental effect on overall product desirability to consumers; results suggested that PPP may significantly enhance appearance of this product. However, for beef snack sticks the cooking out of fat and moisture during PPP had a significant negative effect on consumer opinions of product appearance.

Fate of Staphylococcus aureus on vacuum-packaged ready-to-eat meat products stored at 21 degrees C.

The U.S. Department of Agriculture has established standards for the composition and shelf stability of various ready-to-eat meat products. These standards may include product pH, moisture:protein ratio, and water activity (aw) values. It is unclear how closely these standards are based on the potential for pathogen growth or toxin production. Because the vacuum packaging used on most ready-to-eat meat products inhibits mold, Staphylococcus aureus is the pathogen most likely to grow on products with reduced aw and increased percentage of water-phase salt. In this study, 34 samples of various ready-to-eat meat products were inoculated with a three-strain mixture of S. aureus, vacuum packaged, and stored at 21 degrees C for 4 weeks. S. aureus numbers decreased by 1.1 to 5.6 log CFU on fermented products (pH < or = 5.1) with a wide range of salt concentrations and moisture content. Similarly, S. aureus numbers decreased by 3.2 to 4.5 log CFU on dried nonacidified jerky (aw < or = 0.82; moisture:protein ratio of < or =0.8). Products that were not fermented or dried clearly supported S. aureus growth and cannot be considered shelf stable. The product pH and moisture:protein ratio were the two compositional factors most highly correlated (R2 = 0.84) with S. aureus survival and growth for the types of products tested, but pH and aw or pH and percentage of water-phase salt also may provide useful predictive guidance (R2 = 0.81 and 0.77, respectively).

Growth of Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus during thawing of whole chicken and retail ground beef portions at 22 and 30 degrees C.

Food regulatory agencies advise against thawing frozen meat and poultry at room temperature. In this study, whole chickens (1,670 g) and ground beef (453 and 1,359 g) were inoculated with Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus on the surface (all products) and in the center (ground beef). After freezing at -20 degrees C for 24 h, products were thawed at 22 or 30 degrees C for 9 h. Pathogen growth was predicted using product time and temperature data and growth values from the U.S. Department of Agriculture Agricultural Research Service Pathogen Modeling Program 7.0 predictive models of pathogen growth. No pathogen growth was predicted for whole chicken or 1,359 g of ground beef thawed at 30 degrees C or 453 g of ground beef thawed at 22 degrees C. Growth (< or = 5 generations) was predicted for 453 g of ground beef at 30 degrees C. Inoculation study data corroborated the predictions. No growth occurred on whole chickens or 1,359-g portions of ground beef thawed at 30 degrees C for 9 h. Pathogen numbers increased an average of 0.2 to 0.5 log on the surface of 453-g ground beef portions thawed for 9 h at 22 or 30 degrees C. Our results suggest that thawing > or = 1,670 g of whole chicken at < or = 30 degrees C for < or = 9 h and thawing >453 g ground beef portions at < or = 22 degrees C for < or = 9 h are not particularly hazardous practices. Thawing smaller portions at higher temperatures and/or for longer times cannot be recommended, however. Use of values derived from the Pathogen Modeling Program 7.0 model provided realistic predictions of pathogen growth during thawing of frozen ground beef and chicken.

Evaluation of fertilization-to-planting and fertilization-to-harvest intervals for safe use of noncomposted bovine manure in Wisconsin vegetable production.

Fresh bovine manure was mechanically incorporated into loamy sand and silty clay loam Wisconsin soils in April 2004. At varying fertilization-to-planting intervals, radish, lettuce, and carrot seeds were planted; crops were harvested 90, 100, 110 or 111, and 120 days after manure application. As an indicator of potential contamination with fecal pathogens, levels of Escherichia coli in the manure-fertilized soil and presence of E. coli on harvested vegetables were monitored. From initial levels of 4.0 to 4.2 log CFU/g, E. coli levels in both manure-fertilized soils decreased by 2.4 to 2.5 log CFU/g during the first 7 weeks. However, E. coli was consistently detected from enriched soil samples through week 17, perhaps as a result of contamination by birds and other wildlife. In the higher clay silty clay loam soil, the fertilization-to-planting interval affected the prevalence of E. coli on lettuce but not on radishes and carrots. Root crop contamination was consistent across different fertilization-to-harvest intervals in silty clay loam, including the National Organic Program minimum fertilization-to-harvest interval of 120 days. However, lettuce contamination in silty clay loam was significantly (P < 0.10) affected by fertilization-to-harvest interval. Increasing the fertilization-to-planting interval in the lower clay loamy sand soil decreased the prevalence of E. coli on root crops. The fertilization-to-harvest interval had no clear effect on vegetable contamination in loamy sand. Overall, these results do not provide grounds for reducing the National Organic Program minimum fertilization-to-harvest interval from the current 120-day standard.

Comparison of the Baird-Parker agar and 3M Petrifilm Staph Express Count plate methods for enumeration of Staphylococcus aureus in naturally and artificially contaminated foods.

The recently developed 3M Petrifilm Staph Express Count plate (PFSE) method was compared with the U.S. Food and Drug Administration Bacteriological Analytical Manual's Baird-Parker agar spread plate (B-P) method for enumeration of Staphylococcus aureus in naturally contaminated, mechanically separated poultry (MSP; n = 92) and raw milk (n = 12). In addition, mozzarella and Parmesan cheeses and hot-smoked rainbow trout and chub were surface inoculated with a three-strain mixture of S. aureus, stored at 5 degrees C, and periodically analyzed with both methods for numbers of S. aureus. For naturally contaminated raw milk and MSP samples, the PFSE method yielded counts that were not significantly different (P > 0.05) from counts obtained using the B-P method. From raw milk and MSP samples, 60% (21 of 35) and 55% (124 of 226), respectively, of confirmed (DNAse-positive) isolates from PFSE plates were identified by further testing as S. aureus. Corresponding S. aureus identification rates for isolates forming typical colonies on B-P plates were 53% (19 of 36) and 50% (125 of 248). For both methods, other staphylococci composed the vast majority of tested isolates that were not identified as S. aureus. For inoculated hot-smoked fish, S. aureus counts from the PFSE method were not significantly different from counts from the B-P method. Compared to the B-P method, significantly lower numbers of inoculated S. aureus were recovered using the PFSE method in analyses of mozzarella cheese stored 28 and 42 days at 4 degrees C. The PFSE and B-P methods were not significantly different for inoculated cheeses at all other sampling times. DNAse-positive isolates from PFSE analyses of inoculated cheeses and smoked fish were identified as S. aureus 98% (51 of 52) and 86% (36 of 42) of the time, respectively, as compared with 100% (58 of 58) and 95% (40 of 42) of the time for typical B-P isolates. Overall, the PFSE and B-P methods appeared to perform similarly in enumeration of S. aureus in animal-derived foods.