H7 In Raw Ground Beef Research Articles

Studies on Simultaneous Enrichment and Detection of Escherichia coli O157:H7 during Sample Shipment.

The USDA-FSIS has zero tolerance for E. coli O157:H7 in raw ground beef. Currently, FSIS collects samples from beef processing facilities and ships them overnight to regional testing laboratories. Pathogen detection requires robust methods that employ an initial 15-24 h culture enrichment. This study assessed the potential of using the ΦV10nluc phage-based luminescence detection assay during enrichment while the sample is in transit. Parameters including phage concentrations, temperature, and media-to-sample ratios were evaluated. Results in liquid media showed that 1.73× 103 pfu/mL of ΦV10nluc was able to detect 2 CFU in 10 h. The detection of E. coli O157:H7 was further evaluated in kinetic studies using ratios of 1:3, 1:2, and 1:1 ground beef sample to enrichment media, yielding positive results for as little as 2-3 CFU in 325 g ground beef in about 15 h at 37 °C. These results suggest that this approach is feasible, allowing the detection of a presumptive positive upon arrival of the sample to the testing lab. As the current cargo hold controlled temperature is required to be 15-25 °C, the need for elevated temperature should be easily addressed. If successful, this approach could be expanded to other pathogens and foods.

Dynamic analysis of competitive growth of Escherichia coli O157:H7 in raw ground beef

The objective of this study was to investigate the growth of Escherichia coli O157:H7 in raw ground beef under competition from background flora. The growth of E. coli O157:H7 was observed in sterile irradiated and non-irradiated raw ground beef under dynamically changing temperature conditions. A one-step dynamic analysis method was used to directly construct tertiary models for describing bacterial growth with and without competition and to estimate the kinetic parameters from dynamic growth curves to prove the hypothesis that the growth of E. coli O157:H7 was significantly affected by competition from background flora in raw ground beef.The one-step dynamic method successfully modelled the growth of E. coli O157:H7 and background flora in ground beef and the competition between the two. The estimated minimum growth temperature for E. coli O157:H7 was 7.7 °C, and the maximum cell concentration was 9.0 log CFU/g in irradiated ground beef. Under competition, the specific growth rate of E. coli O157:H7 was reduced by approximately 18% in raw ground beef. The resulting dynamic models and kinetic parameters were validated with separate dynamic growth data, showing that the Root Mean Square Error (RMSE) of prediction was <0.5 log CFU/g for both background flora and E. coli O157:H7. In addition, the models were validated with the growth data of background flora and non-O157 Shiga toxin-producing E. coli (STEC) in raw ground beef obtained in a previous study, also yielding a RMSE of <0.5 log CFU/g. This result also suggests that the growth kinetics of E. coli O157:H7 and non-O157 STEC may be similar in ground beef.The results of this study demonstrated that the one-step dynamic analysis is a useful and efficient method for investigating bacterial growth with and without competition under dynamic conditions and for developing growth kinetic models. Since the dynamic models have been validated, they can be used to predict the shelf-life of ground beef (background flora) and conduct risk assessment of E. coli O157:H7 and non-O157 STEC.

Evaluation of mericon E. coli O157 Screen Plus and mericon E. coli STEC O-Type Pathogen Detection Assays in Select Foods: Collaborative Study, First Action 2017.05.

QIAGEN mericon Escherichia coli O157 Screen Plus and mericon E. coli Shiga toxin-producing E. coli (STEC) O-Type Pathogen Detection Assays use Real-Time PCR technology for the rapid, accurate detection of E. coli O157 and the "big six" (O26, O45, O103, O111, O121, O145) (non-O157 STEC) in select food types. Using a paired study design, the assays were compared with the U.S. Department of Agriculture, Food Safety Inspection Service Microbiology Laboratory Guidebook Chapter 5.09 reference method for the detection of E. coli O157:H7 in raw ground beef. Both mericon assays were evaluated using the manual and an automated DNA extraction method. Thirteen technicians from five laboratories located within the continental United States participated in the collaborative study. Three levels of contamination were evaluated. Statistical analysis was conducted according to the probability of detection (POD) statistical model. Results obtained for the low-inoculum level test portions produced a difference between laboratories POD (dLPOD) value with a 95% confidence interval of 0.00 (-0.12, 0.12) for the mericon E. coli O157 Screen Plus with manual and automated extraction and mericon E. coli STEC O-Type with manual extraction and -0.01 (-0.13, 0.10) for the mericon E. coli STEC O-Type with automated extraction. The dLPOD results indicate equivalence between the candidate methods and the reference method.

Detection of E. coli O157:H7 in raw ground beef by Pathatrix™ immunomagnetic-separation, real-time PCR and cultural methods

Detection of Escherichia coli O157:H7 by conventional cultural methods can be difficult in food matrices with a high background flora such as raw ground beef. Raw ground beef samples, artificially contaminated separately with five strains of E. coli O157:H7 at low (~0.2 cfu/g) and high (~2 cfu/g) levels, were enriched by two enrichment protocols; buffered peptone water (BPW) at 37 °C for 5h and 24h and modified buffered peptone water with pyruvate (mBPWp) for 5h at 37 °C followed by adding selective agents and incubating at 42 °C to 24h. Detection of added E. coli O157:H7 by real-time PCR (RTiPCR) and recovery on isolation agars was performed before and after PATHATRIX™ immunomagnetic separation (IMS). RTiPCR detection and cultural recovery of inoculated E. coli O157:H7 after 5h enrichment were poor at 0.21-0.24 cfu/g. The addition of IMS after 5h enrichment did not improve RTiPCR detection but markedly improved recovery by culturing. By extending enrichment to 24h, RTiPCR detection improved to 76% for either enrichment protocol without IMS. When 24h enrichment was followed by IMS, RTiPCR detection was also further improved. Cultural recovery after 24h enrichment was 56% and 84% without IMS and 100% and 92% after IMS for BPW and mBPWp respectively. Extended enrichment to 24h followed by IMS was found to be sensitive and reliable for detection and cultural recovery from raw ground beef using either enrichment method.

USDA FSIS, FDA BAM, and ISO Culture Methods BD BBL CHROMagar O157 Media

BBL CHROMagar O157 media (CO) was evaluated for detection of Escherichia coli O157:H7 in raw ground beef and unpasteurized apple cider. The recovery of E. coli O157:H7 on CO was compared to the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM), U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS), and International Organization for Standardization (ISO) reference-plated media using the recommended enrichment broths. Of the 180 food samples tested, 45 were tested using BAM, 45 using the USDA method, and 90 using the ISO method. CO produced comparable results with the reference methods on all matrixes with a sensitivity of 100% and a specificity of 100%. No false negatives were found in testing the food matrixes. There was no statistical difference in recovery based on Chi-square analysis. Method agreement for raw ground beef was 85% for the USDAFSIS method and 95% for the ISO method. Method agreement for unpasteurized apple cider was 100% for the ISO and FDA BAM methods. In all cases where method agreement was <100%, CO detected more positives than the reference method media. Evaluation of known isolates on CO in inclusivity and exclusivity testing had a sensitivity and specificity of 100%. The results of this study demonstrate that CO is an effective medium for the recovery and detection of E. coli O157:H7 in raw ground beef and unpasteurized apple cider using FDA BAM, USDA FSIS, and ISO methods.

Thermal destruction of Escherichia coli O157:H7 in sous-vide cooked ground beef as affected by tea leaf and apple skin powders.

We investigated the heat resistance of a four-strain mixture of Escherichia coli O157:H7 in raw ground beef in both the absence and presence of white and green tea powders and an apple skin extract. Inoculated meat was cooked using the sous-vide technique, i.e., the meat was packaged in sterile bags and completely immersed in a circulating water bath at low temperature for a period of time. The bags were cooked for 1 h to an internal temperature of 55, 58, 60, or 62.5 degrees C, and then held from 240 min at 55 degrees C to 10 min at 62.5 degrees C. The surviving bacteria were enumerated by spiral plating onto tryptic soy agar overlaid with sorbitol-MacConkey agar. Inactivation kinetics of the pathogens deviated from first-order kinetics. D-values (time, in minutes, required for the bacteria to decrease by 90%) in the control beef ranged from 67.79 min at 55 degrees C to 2.01 min at 62.5 degrees C. D-values determined by a logistic model ranged from 36.22 (D1, the D-value of a major population of surviving cells) and 112.79 (D2, the D-value of a minor subpopulation) at 55 degrees C to 1.39 (D1) and 3.00 (D2) at 62.5 degrees C. A significant increase (P < 0.05) in the sensitivity of the bacteria to heat was observed with the addition of 3% added antimicrobials. D-value reductions of 62 to 74% were observed with apple powder and 18 to 58% with tea powders. Thermal death times from this study will assist the retail food industry to design cooking regimes that ensure the safety of beef contaminated with E. coli O157:H7.

Carvacrol and cinnamaldehyde facilitate thermal destruction of Escherichia coli O157:H7 in raw ground beef.

The heat resistance of a four-strain mixture of Escherichia coli O157:H7 in raw ground beef in both the absence and presence of the antimicrobials carvacrol and cinnamaldehyde was tested at temperatures ranging from 55 to 62.5 degrees C. Inoculated meat packaged in bags was completely immersed in a circulating water bath, cooked for 1 h to an internal temperature of 55, 58, 60, or 62.5 degrees C, and then held for predetermined lengths of time ranging from 210 min at 55 degrees C to 5 min at 62.5 degrees C. The surviving bacteria were enumerated by spiral plating onto tryptic soy agar overlaid with sorbitol MacConkey agar. Inactivation kinetics of the pathogens deviated from first-order kinetics. D-values (time for the bacteria to decrease by 90%) in the control beef ranged from 63.90 min at 55 degrees C to 1.79 min at 62.5 degrees C. D-values determined by a logistic model ranged from 43.18 min (D1, the D-value of a major population of surviving cells) and 89.84 min (D2, the D-value of a minor subpopulation) at 55 degrees C to 1.77 (D1) and 0.78 min (D2) at 62.5 degrees C. The thermal death times suggested that to achieve a 4-D reduction, contaminated processed ground beef should be heated to an internal temperature of 60 degrees C for at least 30.32 min. Significantly increased sensitivity to heat (P < 0.05) was observed with the addition and/or increasing levels of carvacrol or cinnamaldehyde from 0.5 to 1.0%. The observed thermal death times may facilitate the design of acceptance limits at critical control points for ground beef at lower times and temperatures of heating.

Trends and opportunities in food pathogen detection

Despite the recent advances in food pathogen detection, there still exist many challenges and opportunities to improve the current technology. Techniques such as immunomagnetic separation (IMS) and polymerase chain reaction (PCR) have paved the way for rapid and sensitive detection of foodborne pathogens, and advances in nanobiotechnology have allowed for miniaturization of devices. Collaborations between workers in the fields of engineering, nanotechnology and food science have introduced new lab-on-a-chip technologies permitting development of portable, hand-held biosensors for food pathogen detection. This report highlights examples within the current state of the art, and emphasizes areas in which further research is needed. In 1999 it was estimated that foodborne pathogens were responsible for 76 million illnesses annually, resulting in 5,000 deaths [1]. This report identified Salmonella, Listeria and Toxoplasma as the major causative agents, being responsible for 1,500 of the reported deaths. Data published in 2006 by the CDC suggested that infections due to Yersinia, Shigella, Listeria, Campylobacter, Escherichia coli O157:H7 and Salmonella have decreased dramatically, while infections due to Vibrio have increased [2]. A more recent report indicated similar findings, with a decrease in Yersinia, Shigella, Listeria and Campylobacter cases, and again a significant increase in Vibrio infections [3]. The declining rates of infection due to Listeria monocytogenes and E. coli O157:H7 are likely a result of increased awareness. The FDA, USDA and EU have all implemented a zero-tolerance rule for L. monocytogenes in ready-to-eat (RTE) foods. Similarly, the USDA’s Food Safety and Inspection Service (USDA-FSIS) has declared E. coli O157:H7 in raw ground beef to be an adulterant and therefore unfit for human consumption. Food safety practices have vastly improved in the processing environment as a result of these regulatory actions, as evidenced by the decreasing rates of infection by both Listeria and E. coli O157:H7. However, of the 121 foodborne outbreaks reported through FoodNet in 2005, almost half (49%) of the reported cases were attributed to noroviruses, and the number of Vibrio infections is on the rise [2]. Therefore, while the “hot” organism may change and while food safety practices are improving, there remains a growing need for enhanced means of food pathogen detection. In addition to the health risk associated with contaminated foods, there is the often devastating economic impact to the food producer. A 2007 recall of 21. 7 × 106 lb of ground beef owing to contamination with E. coli O157:H7 resulted in the Topps Meat Company going out of business after 67 years of operation. Indeed, the consolidation of food producers in the USA means that the larger companies have a greater responsibility toward protecting the food supply. Coast-to-coast and international distribution by these mega-processing plants puts potential outbreaks on a national and international scale. Increasing automation in food processing facilities increases the risk of contamination by environmental sources following heat treatment, which is a critical concern especially for RTE products. Therefore, monitoring of pathogen counts on processing surfaces is critical in maintaining low or zero counts in food products. The costs of warehousing along with the potential costs of product recalls have potentially made on-site pathogen testing economically advantageous. Faster results would mean that products could go to market earlier. Several companies such as Marshfield Food Safety and IEH now offer on-site testing services for food production facilities. The latter can equip a production facility with modular laboratories that can be brought in, providing faster turnaround results. These needs stem from the increasing number of microbiological tests commissioned for analysis each week. A 2000 study estimated the number of weekly tests commissioned per dairy plant to be 636, followed closely by 444 weekly microbiological tests from processed-food plants [4].

Comparison of Methods for Detection and Isolation of Cold- and Freeze-Stressed Escherichia coli O157:H7 in Raw Ground Beef

A comparison was made of the relative efficiencies of three enrichment media, RapidChek Escherichia coli O157:H7 enrichment broth (REB), R&F broth (RFB), and modified E. coli broth containing novobiocin (mEC+n), and four selective plating media for detection of cold- and freeze-stressed E. coli O157:H7 in raw ground beef. Ground beef (25 g) was inoculated with E. coli O157:H7 at ≤0.5 and ≤2 CFU/g, and samples were then enriched immediately or were stored at 4°C for 72 h or at −20°C for 2 weeks and then enriched. After 8 or 20 h of enrichment, the cultures were plated onto R&F E. coli O157: H7 chromogenic plating medium, cefixime-tellurite sorbitol MacConkey agar, CHROMagar O157, and Rainbow agar O157 and tested using the RapidChek E. coli O157 lateral flow immunoassay and a multiplex PCR assay targeting the E. coli O157: H7 eae, stx1, and stx2 genes. Recovery of E. coli O157:H7 on the four agar media was 4.0 to 7.9 log CFU/ml with the REB enrichment, 1.4 to 7.4 log CFU/ml with RFB, 1.7 to 6.7 log CFU/ml with mEC+n incubated at 42°C, and 1.3 to 3.3 log CFU/ml from mEC+n incubated at 35°C. The percentages of positive ground beef samples containing nonstressed, cold-stressed, and freeze-stressed E. coli O157:H7 as obtained by plating, the immunoassay, and the PCR assay were 97, 88, and 97%, respectively, with REB, 92, 81, and 78%, respectively, with RFB, 97, 58, and 53%, respectively, with mEC+n incubated at 42°C, and 22, 31, and 25%, respectively, with mEC+n incubated at 35°C. Logistic regression analyses of the data indicated significant main effects of treatment, type of medium, enrichment time, inoculum concentration, and detection method. In particular, a positive result was 1.1 times more likely to occur after 20 h of enrichment than after 8 h, 25 times more likely with RFB and REB than with mEC+nat35°C, 3.7 times more likely with an initial inoculum of ≤2.0 CFU/g than with ≤0.5 CFU/g, 2.5 to 3 times more likely using freeze-stressed or nonstressed bacteria than with cold-stressed bacteria, and 2.5 times more likely by plating than by the immunoassay or the PCR assay. REB had better overall performance for enrichment of cold- and freeze-stressed E. coli O157:H7 present in ground beef than did the other media examined.

Food Safety and Inspection Service Regulatory Testing Program for Escherichia coli O157:H7 in Raw Ground Beef

We analyzed raw ground beef testing data to determine whether a decrease in the rate of Escherichia coli O157:H7–positive raw ground beef samples has occurred since the inception of Food Safety and Inspection Service (U.S. Department of Agriculture) regulatory actions and microbiological testing concerning this commodity and pathogen. A main effects log-linear Poisson regression model was constructed to evaluate the association between fiscal year and the rate of E. coli O157: H7–positive raw ground beef samples while controlling for the effect of season for the subset of test results obtained from fiscal year (FY)2000 through FY2003. Rate ratios were used to compare the rate of E. coli O157:H7–positive raw ground beef samples between sequential years to identify year-to-year differences. Of the 26,521 raw ground beef samples tested from FY2000 through FY2003, 189 (0.71%) tested positive for E. coli O157:H7. Year-to-year comparisons identified a 50% reduction in the rate of positive ground beef samples from FY2002 to FY2003 when controlling for season (95% CI, 10 to 72% decrease; P = 0.02). This decrease was the only significant year-to-year change in the rate of E. coli O157:H7–positive raw ground beef samples but was consistent in samples obtained from both federally inspected establishments and retail outlets. We believe this decrease is attributed to specific regulatory actions by Food Safety and Inspection Service and subsequent actions implemented by the industry, with the goal of reducing E. coli O157:H7 adulteration of raw ground beef. Continued monitoring is necessary to confirm that the decrease in the rate of E. coli O157:H7 in raw ground beef samples we observed here represents the beginning of a sustained trend.

Detection ofEscherichia coliO157:H7 andListeria monocytogenesin Beef Products by Real-Time Polymerase Chain Reaction

Rapid methods for the detection of Escherichia coli O157:H7 and Listeria monocytogenes in food products are important to the food industry and for public health. Conventional microbiological methods and newly developed molecular-based techniques such as polymerase chain reaction (PCR)-based methods are time consuming. In this study, a faster method based on utilization of a hybridization probe with real-time PCR, was developed and applied for detection of E. coli O157:H7 and L. monocytogenes from artificially contaminated raw ground beef and fully cooked beef hotdogs. Target genes for E. coli O157:H7 and L. monocytogenes were rfbE and hylA, respectively. An analysis of 169 bacterial strains showed that the chosen primers and probes were specific for detection of E. coli O157:H7 and L. monocytogenes by real-time PCR. The assay was positive for nine of 10. E. coli O157:H7 strains, and all L. monocytogenes (7/7) strains evaluated. Bacterial strains lacking these genes were not detected by these assays. Detection limits of real-time PCR assays ranged from 10(3) to 10(8) colony forming units (CFU)/ml for E. coli O157:H7 in modified tryptic soy broth and 10(4) to 10(8) CFU/mL for L. monocytogenes in Fraser Broth. Detection sensitivity ranged from 10(3) to 10(4) CFU/g of raw ground beef or hotdog without enrichment for E. coli and L. monocytogenes. Approximately 1.4-2.2 CFU/g of E. coli O157:H7 in raw ground beef were detected following an enrichment step of 4 h. Approximately 1.2-6.0 CFU/g of L. monocytogenes in beef hotdogs were detected following an enrichment step of 30 h. The real-time PCR assays for detection of E. coli O157:H7 and L. monocytogenes in raw ground beef and beef hotdogs were specific, sensitive and rapid.

Growth of Escherichia coli O157:H7 in Raw Ground Beef Stored at 10° C and the Influence of Competitive Bacterial Flora, Strain Variation, and Fat Level

Pure-culture broth-based models of the growth of Escherichia coli O157:H7 have been used to estimate its behavior in ground beef, even though these models have not been adequately validated for this food product. This situation limits accurate estimates of the behavior of E. coli O157:H7 in ground beef and introduces uncertainties in risk assessments. In the present study, the growth of single and multiple strains of E. coli O157:H7 were measured in retail ground beef stored at 10°C for up to 12 days, and the results were compared with estimates generated by the U.S. Department of Agriculture's Pathogen Modeling Program (PMP; version 5.1). At pH 5.9, the PMP predicted a maximum population density (MPD) of 9.13 log10 CFU/g, an exponential growth rate (EGR) of 0.052 log10 CFU/h, and a lag time of 56.3 h. Similar parameter values were observed for sterilized ground beef; however, no lag phase was observed. In contrast, the mean MPD and EGR for retail ground beef were 5.09 log10 CFU/g and 0.019 log10 CFU/h, respectively, and no lag phase was observed. Both the EGR and the MPD increased with decreasing fat levels. There was low variation in the MPD and EGR parameters for the nine E. coli O157:H7 ground beef isolates. Two isolates of competitive native flora were separately added to sterilized ground beef, and the EGR and MPD decreased as the ratio of competitive flora to E. coli O157:H7 increased. For one strain, at ratios of 1:1, 10:1, and 100:1, the EGRs were 0.033, 0.025, and 0.018 log10 CFU/h, respectively, and the MPDs were 6.14, 5.08, and 4.84 log10 CFU/g, respectively. These results demonstrate that existing broth-based models for E. coli O157:H7 must be validated for food and that models should consider the effects of the food matrix, the competitive microflora, and potential pathogen strain variation.

Reveal 8-Hour Test System for Detection of Escherichia coli O157:H7 in Raw Ground Beef, Raw Beef Cubes, and Iceberg Lettuce Rinse: Collaborative Study

Five different food types were analyzed by the Reveal for E. coli O157:H7 8-Hour Test System (Reveal 8) and either the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) culture method or the U.S. Department of Agriculture Food Safety Inspection Service (FSIS) culture method for the presence of E. coli O157:H7. A total of 27 laboratories representing academia and private industry in the United States and Canada participated. Food types were inoculated with E. coli O157:H7 at 2 different levels: a high level where predominantly positive results were expected, and a low level where fractional recovery was anticipated. During this study, 1,110 samples and controls were analyzed by both the Reveal 8 and by BAM or FSIS by each of the collaborators (2,220 samples in total). For each set of samples, 740 were artificially inoculated with E. coli O157:H7, and 370 were uninoculated controls. The Reveal 8 detected 528 presumptive positives of which 487 were confirmed positive by the BAM culture method. In comparison, BAM and FSIS detected 489 of the 740 artificially contaminated samples as positive. In an additional in-house study performed only on chilled and frozen raw ground beef, 240 artificially inoculated samples were analyzed by both the Reveal 8 and by FSIS. The Reveal 8 detected and confirmed 104 samples as positive compared to 79 confirmed positive by FSIS.

Comparison of the Difco EZ Coli™ Rapid Detection System and Petrifilm™ Test Kit-HEC for Detection of Escherichia coli O157:H7 in Fresh and Frozen Ground Beef

The Difco EZ Coli™ Rapid Detection System was compared to the 3M Petrifilm™ method for detection of Escherichia coli O157:H7 in raw ground beef. Raw meatballs (25 g) were inoculated with 10 to 15 cells of Escherichia coli O157:H7, stored for various times and at different temperatures, and then stomached for 2 min in 225 ml of EZ Coli™ enrichment broth, which was then incubated at 42°C for 18 to 24 h. A 1-ml sample of the enrichment broth was loaded into the top of the detector tips and the remaining EZ Coli™ broth held at 35°C before streaking onto MacConkey sorbitol agar and tryptic soy agar with yeast extract. A duplicate set of meatballs were tested using the 3M Petrifilm™ Test Kit-HEC for hemorrhagic Escherichia coli O157:H7. In this method raw meatballs (25 g) were enriched for 6 h in modified EC broth containing novobiocin at 37°C prior to inoculation of the Petrifilm™E. coli Count Plates, which were incubated at 42°C for 18 h. The immunoblot ELISA was performed following this incubation. Presumptive positive isolates from both methods were confirmed using Oxoid E. coli Latex Agglutination and Difco Pasco ID Tripanels. Both methods permitted detection of 10 to 15 cells of E. coli O157:H7 per ml (i) immediately following inoculation, (ii) after 3 days of refrigerated storage at 8°C, and (iii) after 30 days in frozen storage at −20°C. The Difco EZ Coli™ Detection System proved to be a simpler and faster screening method with identification of negative and presumptive positive samples within 15 to 18 h

Validation of Predictive Mathematical Models Describing the Growth of Escherichia coli O157:H7 in Raw Ground Beef

The growth of Escherichia coli O157:H7 in raw ground beef was investigated at 12°C, 20°C, and 35°C at pH 5.7 (unadjusted) and adjusted to pH 6.3 to 6.4. These growth data were fitted to the Gompertz equation and the resulting growth kinetics were compared with predictions from the U.S. Department of Agriculture Pathogen Modeling Program. Close agreement with the model was obtained at pH 5.7, but at pH 6.4, growth was more rapid than predicted. The U.S. Department of Agriculture Food Safety and Inspection Service has used this predictive model for developing proposed regulations on time-temperature requirements for carcass cooling. As there may be considerable differences in the microenvironment of raw ground beef and a beef carcass, the validity of using predictive models for estimating growth rates on a carcass should be determined by performing growth studies on carcass surfaces.