Fresh Ground Beef Research Articles

Fate ofEscherichia coliO157:H7 in ground beef following high-pressure processing and freezing

The purposes of this study were to evaluate the efficacy of high pressure to inactivate Escherichia coli O157:H7 in ground beef at ambient and subzero treatment temperatures and to study the fate of surviving bacteria postprocess and during frozen storage. Fresh ground beef was inoculated with a five-strain cocktail of E. coli O157:H7 vacuum-packaged, pressure-treated at 400 MPa for 10 min at -5 or 20 degrees C and stored at -20 or 4 degrees C for 5-30 days. A 3-log CFU g(-1) reduction of E. coli O157:H7 in the initial inoculum of 1 x 10(6) CFU g(-1) was observed immediately after pressure treatment at 20 degrees C. During frozen storage, levels of E. coli O157:H7 declined to <1 x 10(2) CFU g(-1) after 5 days. The physiological status of the surviving E. coli was affected by high pressure, sensitizing the cells to pH levels 3 and 4, bile salts at 5% and 10% and mild cooking temperatures of 55-65 degrees C. High-pressure processing (HPP) reduced E. coli O157:H7 in ground beef by 3 log CFU g(-1) and caused substantial sublethal injury resulting in further log reductions of bacteria during frozen storage. HPP treatment of packaged ground beef has potential in the meat industry for postprocess control of pathogens such as E. coli O157:H7 with enhanced safety of the product.

Evaluation of the effect of defrosting practices of ground beef on the heat tolerance of Listeria monocytogenes and Salmonella Enteritidis

The effect of common defrosting practices of ground beef, including (i) defrosting in the refrigerator (5 °C for 15 h), (ii) defrosting at room temperature (25 °C for 12 h) and (iii) defrosting in the microwave, on the heat tolerance of artificially inoculated Listeria monocytogenes and Salmonella Enteritidis, was studied. The thermal inactivation of S. Enteritidis was not, overall, affected by defrosting practices. In contrast, defrosting at room temperature resulted, overall, in an increased heat tolerance of L. monocytogenes compared to the rest tested defrosting practices. Inactivation kinetics of the two pathogens for the different defrosting practices were determined by fitting the data to the Weibull model. The δ parameter of the Weibull model (heat challenge time (min) required for the first 1-log reduction) for S. Enteritidis and for defrosting at 25 °C, microwave defrosting, defrosting at 5 °C and for the control (fresh ground beef inoculated with the pathogens just before the heat challenge trials) was 1.13, 1.62, 1.60 and 0.96, respectively, while the corresponding values for L. monocytogenes were 20.13, 10.82, 9.95 and 9.47, respectively. The findings of this study should be useful in risk assessments and in developing food handling guidelines for the consumers.

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°C and in fresh raw ground beef at 10 and 5°C. Pathogen inhibition was observed in the broth medium at both high (108:105 to 107:105) and low (106:105 to 105:105) LS:pathogen ratios. After 9 days at 10°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 105:102 to 105:103. Significant inhibition was seen at very high LS:pathogen ratios (106 to 107:102 to 103), 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.

Detection of Escherichia coli O157:H7 in ground beef using immunomagnetic separation and multiplex PCR

In the study 251 fresh ground beef samples sold in Ankara were analyzed to evaluate the prevalence of Escherichia coli O157:H7 by immunomagnetic separation (IMS) based cultivation technique. Virulence factors of the isolates were determined by multiplex PCR. Nineteen (7.6%) of 251 ground beef samples were found as contaminated with E. coli O157. By PCR analyse in two of the isolates fliC h 7 gene was detected and identified as E. coli O157:H7. According to the multiplex PCR one of the isolate has all stx 1, stx 2, eaeA, hly and fliC h 7 genes and the other has stx 1, eaeA, hly and fliC h 7 genes.

Identification of main contamination points by hygiene indicator microorganisms in beef processing plants

The microbiological quality of beef and meat products is strongly influenced by the conditions of hygiene prevailing during their production and handling. Without proper hygienic control, the environment in slaughterhouses and butcher shops can act as an important source of microbiological contamination. To identify the main points of microbiological contamination in the beef processing chain, 443 samples of equipment, installations and products were collected from 11 establishments (1 slaughterhouse and 10 butcher shops) located in the state of Parana, Brazil. The microbiological quality of all the samples was evaluated using Petri dishes to obtain counts of mesophilic aerobes (AC), total coliforms, Escherichia coli (EC), yeasts and molds (YM). The main contamination points identified in butcher shops, in decreasing order, were stainless steel boxes, beef tenderizers, grinders, knives, mixers, sausage stuffers, plastic boxes, floors and drains. In the slaughterhouse, these points were sausage stuffers, platforms, floors and drains. The most severely contaminated products were fresh sausages and ground beef. This information about the main points of microbiological contamination in the beef processing chain is expected to aid professionals responsible for hygiene in similar establishments to set up proper hygienic procedures to prevent or reduce microbiological contamination of beef and meat products.

Knowledge, Attitude, and Practice of the Use of Irradiated Meat among Respondents to the FoodNet Population Survey in Connecticut and New York

Irradiation of fresh meat to control microbial pathogens received approval from the federal government in February 2000. Food irradiation is a useful, albeit underutilized, process that can help protect the public from foodborne illnesses. The objective of this study was to determine consumer knowledge, attitudes, and practices toward irradiated meat products. Data were obtained from a single-stage random-digit dialing telephone survey of residents of the Foodborne Diseases Active Surveillance Network (FoodNet) sites conducted in 2002 to 2003, which included supplemental questions about food safety and irradiated meat for residents of the Connecticut and New York sites. Thirty-seven percent of 3,104 respondents knew that irradiated fresh meat was available for purchase; however, only 2% found the product where they shopped. Knowledge of product availability was significantly influenced by whether a respondent lived in a county with one or more grocery stores operated by chain A, which had actively promoted the sale of irradiated fresh ground beef during the survey period. In a logistic regression model, after adjusting for other factors, respondents living in a county with chain A were more likely to know that irradiated products could be purchased than respondents living in other counties (odds ratio 2.0; 95% confidence interval 1.5 to 2.5). This finding suggests that public education efforts by an individual grocery store chain can have an important effect on knowledge of irradiated food.

Follow the leader? Adoption behavior in food retailers' decision to offer fresh irradiated ground beef

AbstractDuring the 14‐month period from May 2002 through June 2003, approximately 10% of U.S. supermarkets began to offer fresh irradiated ground beef under the stores' own labels. Using a survey of supermarket store managers from this period, the authors investigate the factors that influenced stores' adoption of irradiated ground beef. Results from the adoption model show that factors associated with competition, merchandising philosophy, and structure in the food retailing industry play a strong role in the decision. Among other results, it was found that variables relating to a competitor's adoption status and proximity can increase the likelihood of a store's adoption. [EconLit citations: L660, M310, Q180] © 2006 Wiley Periodicals, Inc. Agribusiness 22: 547–568, 2006.

Validation of Time and Temperature Values as Critical Limits for the Control of Escherichia coli O157:H7 during the Production of Fresh Ground Beef

In order to provide beef processors with valuable data to validate critical limits set for temperature during grinding, a study was conducted to determine Escherichia coli O157:H7 growth at various temperatures in raw ground beef. Fresh ground beef samples were inoculated with a cocktail mixture of streptomycin-resistant E. coli O157:H7 to facilitate recovery in the presence of background flora. Samples were held at 4.4, 7.2, and 10°C, and at room temperature (22.2 to 23.3°C) to mimic typical processing and holding temperatures observed in meat processing environments. E. coli O157:H7 counts were determined by direct plating onto tryptic soy agar with streptomycin (1,000 μg/ml), at 2-h intervals over 12 h for samples held at room temperature. Samples held under refrigeration temperatures were sampled at 4, 8, 12, 24, 48, and 72 h. Less than one log of E. coli O157:H7 growth was observed at 48 h for samples held at 10°C. Samples held at 4.4 and 7.2°C showed less than one log of E. coli O157:H7 growth at 72 h. Samples held at room temperature showed no significant increase in E. coli O157:H7 counts for the first 6 h, but increased significantly afterwards. These results illustrate that meat processors can utilize a variety of time and temperature combinations as critical limits in their hazard analysis critical control point plans to minimize E. coli O157:H7 growth during the production and storage of ground beef.

Effects of peanut skin extract on quality and storage stability of beef products

Peanut skins are a low-value byproduct of peanut processing operations. They have been found to contain significant levels of natural antioxidants, but their antioxidant activity in muscle foods is unknown. The effects of peanut skin extracts on oxidation (TBARS) and color (CIE L ∗ a ∗ b ∗) was studied in ground beef and ground beef with added salt, phosphate (STP) and nitrite/erythorbate. Cooking loss, microbial growth, aroma acceptability and texture were also examined. The most significant reduction in oxidation was in ground beef or samples with salt, followed by phosphate (STP) or nitrite/erythorbate. Because of their low effective concentrations (200 ppm), the extracts did not cause color change ( P > 0.05) of the products indicated by CIE L ∗ a ∗ b ∗ value. The extracts had no effect ( P > 0.05) on sensory aroma. The phenolic extract from peanut skin had no effect ( P > 0.05) on the cooking loss of the ground beef as well as the cured and uncured formulated products. The microbial growth in fresh ground beef was not affected (P < 0.05) by the phenolic extract.

Incidence of Enterohemorrhagic Escherichia coli, Escherichia coli O157, Salmonella, and Listeria monocytogenes in Retail Fresh Ground Beef, Sprouts, and Mushrooms

The objective of this study was to determine the prevalence of enterohemorrhagic Escherichia coli (EHEC), E. coli O157, Salmonella, and Listeria monocytogenes in retail food samples from Seattle, Wash. A total of 2,050 samples of ground beef (1,750 samples), mushrooms (100 samples), and sprouts (200 samples) were collected over a 12-month period and analyzed for the presence of these pathogens. PCR assays, followed by culture confirmation were used to determine the presence or absence of each organism. Of the 1,750 ground beef samples analyzed, 61 (3.5%) were positive for EHEC, and 20 (1.1%) of these were positive for E. coli O157. Salmonella was present in 67 (3.8%) of the 1,750 ground beef samples. Of 512 ground beef samples analyzed, 18 (3.5%) were positive for L. monocytogenes. EHEC was found in 12 (6.0%) of the 200 sprout samples, and 3 (1.5%) of these yielded E. coli O157. Of the 200 total sprout samples, 14 (7.0%) were positive for Salmonella and none were positive for L. monocytogenes. Among the 100 mushroom samples, 4 (4.0%) were positive for EHEC but none of these 4 samples were positive for E. coli O157. Salmonella was detected in 5 (5.0%) of the mushroom samples, and L. monocytogenes was found in 1 (1.0%) of the samples.

Reduction of Escherichia coli O157:H7 and Salmonella in Ground Beef Using Lactic Acid Bacteria and the Impact on Sensory Properties

Studies were conducted to determine whether four strains of lactic acid bacteria (LAB) inhibited Escherichia coli O157: H7 and Salmonella in ground beef at 5°C and whether these bacteria had an impact on the sensory properties of the beef. The LAB consisted of frozen concentrated cultures of four Lactobacillus strains, and a cocktail mixture of streptomycin-resistant E. coli O157:H7 and Salmonella were used as pathogens. Individual LAB isolates at 107 CFU/ml were added to tryptic soy broth containing a pathogen concentration of 105 CFU/ml. Samples were stored at 5°C, and pathogen populations were determined on days 0, 4, 8, and 12. After 4 days of storage, there were significant differences in numbers of both pathogens exposed to LAB isolates NP 35 and NP 3. After 8 and 12 days of storage, all LAB reduced populations of both pathogens by an average of 3 to 5 log cycles. A second study was conducted in vacuum-packaged fresh ground beef. The individual LAB isolates resulted in an average difference of 1.5 log cycles of E. coli O157:H7 after 12 days of storage, and Salmonella populations were reduced by an average of 3 log cycles. Following this study, a mixed concentrated culture was prepared from all four LAB and added to ground beef inoculated with pathogen at 108 CFU/g. After 3 days of storage, the mixed culture resulted in a 2.0-log reduction in E. coli O157:H7 compared with the control, whereas after 5 days of storage, a 3-log reduction was noted. Salmonella was reduced to nondetectable levels after day 5. Sensory studies on noninoculated samples that contained LAB indicated that there were no adverse effects of LAB on the sensory properties of the ground beef. This study indicates that adding LAB to raw ground beef stored at refrigeration temperatures may be an important intervention for controlling foodborne pathogens.

Consumers Evaluate Frozen and Grilled Ground Beef and Turkey Product

Consumers are familiar with evaluating the acceptability of fresh and cooked ground beef in grocery stores and restaurants. Consumer acceptability of either fresh or frozen ground beef or ground beef blended with ground turkey has, however, received little attention. The acceptability of the blended beef turkey product is assumed to be relatively high given its origin from the traditional ground meats. Several different combinations of ground beef and ground turkey were evaluated for sensory color/texture differences in frozen and grilled forms by a 115-member consumer taste panel. Their evaluations of both frozen and grilled samples were influenced by previous experience with the combined product in the home and willingness to purchase the new product prior to evaluation of actual samples.

Evaluation of 2-Dodecylcyclobutanone as an Irradiation Dose Indicator in Fresh Irradiated Ground Beef

Alkylcyclobutanones (2-ACBs) are radiolytic products formed when fatty acids are irradiated. These cyclobutanones are unique irradiation byproducts and therefore may serve as indicators of irradiation exposure. As only limited information exists about 2-ACB formation in retail meat products, reliable methods that can quantify 2-ACBs and thus estimate irradiation dose in commercial meat products are desired. The cyclobutanone studied in this experiment was 2-dodecylcyclobutanone (2-DCB), which is formed from palmitic acid. The formation of 2-DCB was evaluated in fresh irradiated ground beef patties at two fat levels. Patties containing 15% and 25% fat were irradiated by electron beam at 1.0, 2.0, 3.0, and 4.5 kGy. Commercially available 1-lb irradiated ground beef chubs with different fat levels were analyzed in order to estimate dose absorbed by these samples. The 2-DCB was extracted using supercritical fluid extraction (SFE) and analyzed by gas chromatography-mass spectroscopy (GC-MS) and was detected in all the irradiated samples. The concentration of 2-DCB increased linearly with dose with R2 = 0.9646 for 25% fat samples and R2 = 0.9444 for 15% fat samples. Further, there was no significant difference in 2-DCB concentrations between the two fat levels. The estimated doses applied to the commercial samples ranged between 1.38 and 1.55 kGy, values consistent with doses normally used in the industry (1.0-2.0 kGy). Our results show that 2-DCB can be used to monitor fresh irradiated beef and approximate the absorbed dose.

Inactivation of Escherichia coli O157:H7 in packaged ground beef by allyl isothiocyanate

Commercial allyl isothiocyanate (AIT) was examined for its ability to reduce numbers of Escherichia coli O157:H7 inoculated in fresh ground beef packaged under nitrogen and stored refrigerated or frozen. A five-strain cocktail of E. coli O157:H7 containing 3 or 6 log 10 cfu/g was inoculated into 100 g ground beef and formed into 10×1-cm patties. A 10-cm diameter filter paper disk treated with AIT suspended in sterile corn oil was placed on top of a single patty. One patty and paper disk were placed in a bag of Nylon/EVOH/PE with O 2 permeability of 2.3 cm 3 m −2 24 h atm at 23 °C. The bags were back-flushed with 100% nitrogen, heat-sealed and stored at 10, 4 and −18 °C for 8, 21 or 35 days, respectively. During storage, the AIT levels in the package headspaces were determined by gas liquid chromatography, and mesophilic bacteria and E. coli O157:H7 were counted. The mesophilic aerobic bacteria in ground beef patties were largely unaffected by the addition of AIT. At an initial population of 3 log 10 cfu/g, E. coli O157:H7 was reduced by AIT to undetectable levels after 18 days at 4 °C or 10 days at −18 °C. In samples inoculated with 6 log 10 cfu/g, a >3 log 10 reduction of E. coli O157:H7 was observed after 21 days at 4 °C, while a 1 log 10 reduction was observed after 8 and 35 days at 10 and −18 °C, respectively. The final AIT concentrations in the headspaces after storage at 10, 4, and −18 °C were 444, 456, and 112 μg/ml at 8, 21, and 35 days, respectively. Results showed that AIT can substantially reduce numbers of E. coli O157:H7 in fresh ground beef during refrigerated or frozen storage.

Use of mustard flour to inactivate Escherichia coli O157:H7 in ground beef under nitrogen flushed packaging

This study was undertaken to determine whether the glucosinolates naturally present in non-deheated mustard flour could serve as a source of allyl and other isothiocyanates in sufficient quantity to kill Escherichia coli O157:H7 inoculated in ground beef at three different levels, during refrigerated storage of the meat under nitrogen. Mustard flour was mixed at 5%, 10% or 20% (w/w) with freshly ground beef, then the beef was inoculated with a cocktail of five strains of E. coli O157:H7 at either 3, 6 or ≤1.6 log 10 cfu/g. The ground beef was formed into 100 g patties and each was placed in a bag of Nylon/EVOH/PE, which was back-flushed with 100% N 2, heat-sealed and stored at 4 °C for ≤21 days. During storage, the allyl isothiocyanate (AIT) levels in package headspaces were determined by gas liquid chromatography. By 21 days, the levels present in treatments were not significantly different. After 21 days storage, there were 0.5, 3 and 5.4 log 10 decreases in numbers of E. coli O157:H7 from the initial levels of 6 log 10 cfu/g in meat containing 5%, 10% and 20% mustard flour, respectively. When inoculated at 3 log 10 cfu/g, E. coli O157:H7 was reduced to undetectable levels after 18, 12 and 3 days with 5%, 10% and 20% mustard flour, respectively. When immunomagnetic separation (IMS) was used for E. coli recovery following its inoculation at ≤1.6 log 10 cfu/g, 5% mustard did not completely eliminate the pathogen from ground beef stored for 6 days. The natural microflora of the ground beef which developed in vacuum packages was unaffected by the addition of 5% mustard flour but some inhibition was found at higher concentrations. Sensory evaluation of the cooked ground beef showed that there were no significant differences in the acceptability of meat treated with 5 or 10% mustard flour. However, panelists could distinguish untreated controls from mustard treatments, but considered the mustard-treated meat to be acceptable. These results showed that it is possible to use mustard flour at levels of >5–10% to eliminate E. coli O157:H7 from fresh ground beef.

Effects of Basil and Majoram Essential Oils with or without Ascorbic Acid on Color and Oxidative and Microbial Stability of Beef Patties

Fresh ground beef was mixed with ascorbic acid, basil essential oil, majoram essential oil, or each essential oil combined with ascorbic acid and stored at 1±1℃ for 7 days. Color, lipid oxidation (TBARS formation), aerobic bacterial counts and pH were determined. Basil and majoram essential oils were effective in inhibiting color deterioration, lipid oxidation and bacterial growth. The combined addition of basil and ascorbic acid showed the highest protection against color fading, followed by majoram＋ascorbic acid, and ascorbic acid alone. Basil and majoram essential oils were most effective in delaying TBARS formation (p＜0.01). Ascorbic acid did not exert an antioxidative effect and even exhibited a pro-oxidant effect. The pH values of all samples increased slightly, but no significant differences were observed, either among treatments or throughout the storage time (p＞0.05).

Rapid Determination of Moisture and Fat in Meats by Microwave and Nuclear Magnetic Resonance Analysis

A peer-verified method is presented for the determination of percent moisture and fat in meat products by microwave drying and nuclear magnetic resonance (NMR) analysis. The method involves determining the moisture content of meat samples by microwave drying and using the dried sample to determine the fat content by NMR analysis. Both the submitting and peer laboratories analyzed 5 meat products by using the CEM SMART system (moisture) and the SMART Trac (fat). The samples, which represented a range of products that meat processors deal with daily in plant operations, included the following: (1) fresh ground beef, high-fat; (2) deboned chicken with skin; (3) fresh pork, low-fat; (4) all-beef hot dogs; and (5) National Institute of Standards and Technology Standard Reference Material. The results were compared with moisture and fat values derived from AOAC-approved methods, 950.46 (Forced Air Oven Drying) and 960.39 (Soxhlet Ether Extraction).

Optimizing Enrichment Culture Conditions for Detecting Helicobacter pylori in Foods

The survival and growth of Helicobacter pylori under enrichment conditions in fresh, autoclaved and irradiated ground beef were determined. H. pylori grew in autoclaved ground beef at 37°C under microaerobic conditions in brain heart infusion broth with 7% horse serum at pH 7.3 after 3 to 7 days of lag time but did not grow within 7 days in irradiated (10 kGy) ground beef under the same enrichment conditions. Adjustment of the enrichment broth to pH 5.5 enabled the growth (ca. 2 log10 CFU/ml) of H. pylori within 7 days in the presence of irradiated ground beef and the prolific growth (ca. 3 to 4 log10 CFU/ml) of H. pylori within 3 days in the presence of autoclaved beef. H. pylori in fresh ground beef could not be isolated from enrichment media with antibiotics; however, H. pylori ureA could be detected by polymerase chain reaction (PCR) in such enrichment media after 1 to 3 days of incubation at 37°C. The addition of supplements, i.e., 0.3% mucin, 0.05% ferrous sulfate, and 0.05% sodium pyruvate or 0.008M urea, or the adjustment of the enrichment broth pH to 5.5 or 4.5 enabled the detection of H. pylori ureA in enrichment media incubated for 1, 2, 3, and/or 7 days at 37°C. H. pylori in sterile milk refrigerated at 4°C at an initial level of 106 CFU/ml was inactivated to an undetectable level within 6 days; however, H. pylori was not detected either by a PCR assay or by the plating of enrichment cultures of 120 raw bovine milk samples.

Profile and activity of the bacterial biota of ground beef held from freshness to spoilage at 5–7 °C

Four samples of fresh ground beef were stored aerobically and held at 5–7 °C for up to 28 days. Although one sample initially yielded 21 different genera of bacteria while two others yielded only seven, all four spoiled essentially in the same way as assessed by aerobic, psychrotrophic, and Gram-negative counts, and by extract-release volume (ERV) and pH values. Pseudomonas spp. was dominant in the spoilage of all samples. As to why this group is so consistently associated with the low-temperature aerobic spoilage of fresh meats, it is hypothesized that they possess the capacity to form a biofilm and that quorum sensing is involved in the overall biofilm forming and functioning processes.

Fate of Field-Isolated Escherichia coli O157 in Ground Beef at Different Storage Temperatures

The survival of six Escherichia coli O157 strains, including five strains recently isolated from beef carcasses and strain ATCC 43895, was evaluated at 0, 1, 7, and 14 days in ground beef held at −20, 1, 4, and 7°C. Only small losses in cell numbers occurred at −20 and 1°C; in general, cell numbers decreased during the first day of storage and then remained unchanged through day 14. At −20°C, statistically significant reductions in cell numbers were observed only for strains 55AC1 and 299AB3 due to greater losses in the first day. At 1°C, strain 131AC1 did not decrease in cell numbers during the first day of storage, but both this strain and strain 55AC1 experienced statistically significant reductions in viable cell numbers by day 14, primarily due to losses after day 7. At 4°C, after an initial loss of cell numbers for four strains, minor increases were observed for all six strains by day 14. The differences were statistically significant for strains 114AC1, 299AB3, and ATCC 43895, but were small enough to question whether they refect actual growth. When the inoculated ground beef was stored at 7°C for 14 days, growth of all six strains was statistically significant, with populations increasing between 0.9 and 1.5 log10 CFU/g. This study demonstrates that there are small differences in the abilities of various E. coli O157 strains to survive and sometimes grow in fresh ground beef at cold storage temperatures, but overall these differences do not appear to be meaningful. The differences cannot be attributed to recency of isolation, since strain ATCC 43895 behaved similarly to recently isolated strains. Storage temperatures of 4°C or below limited growth of E. coli O157 isolates, but did not have a noteworthy effect on survival.