ABSTRACT The U.S. beef industry must provide documentation to the U.S. Department of Agriculture, Food Safety and Inspection Service (USDA-FSIS) that the antimicrobial interventions implemented or any subsequent changes in the process are effective under the actual conditions that apply in its operation. The main objective of this study was to determine whether surface pH after application of diluted lactic acid solution on surfaces of fresh meat can be used as a control measure indicator for the reduction of E. coli O157:H7 and Salmonella . Samples (240 each) of lean and adipose beef tissues were inoculated with cocktail mixtures of Escherichia coli O157:H7 and Salmonella . Application parameters were varied such that lean and adipose tissues were spray treated with either 2 or 4.5% lactic acid solution at either 38 or 60°C for 1 to 10 s. Lean and adipose tissues were collected before and after spray treatments for enumeration of the pathogens. Based on the conditions of this study, there was no difference between spray treatments at 38 or 60°C, but 4.5% lactic acid solution reduced pathogens more effectively ( P ≤ 0.05) than did 2% lactic acid solution. Spray treatment with lactic acid solution for 1 to 10 s reduced surface pH values of lean tissues (3 to 3.8) and adipose tissues (2.75 to 3.65). At surface pH values of 3.0 and 2.75, lactic acid reduced E. coli O157:H7 on surfaces of lean and adipose tissues by approximately 1.60 and 1.54 log CFU/cm 2 , respectively. At surface pH values of 3.8 and 3.65, lactic acid reduced E. coli O157:H7 on lean and adipose tissues by approximately 0.3 and 0.42 log CFU/cm 2 , respectively. The surface pH values after lactic acid treatment and the reductions of both pathogens showed a strong linear relationship; this indicates that a surface pH of 3.1 would provide at least 1-log reduction of E. coli O157:H7 and Salmonella, regardless of lactic acid application parameters. Therefore, surface pH after spray treatment with lactic acid could be used to validate pathogen reduction.

The incidence of Clostridium difficile infection has recently increased in North American and European countries. This pathogen has been isolated from retail pork, turkey, and beef products and reported associated with human illness. This increase in infections has been attributed to the emergence of a toxigenic strain designated North America pulsed-field gel electrophoresis type 1 (NAP1). The NAP1 strain has been isolated from calves as well as ground meat products, leading to speculation of illness from consumption of contaminated meat products. However, information on C. difficile associated with beef cattle during processing and commercially produced ground beef is limited. To address this data gap, samples from various steps during beef production were collected. Samples from hides ( n = 525), preevisceration carcasses ( n = 475), postintervention carcasses ( n = 471), and 956 commercial ground beef samples were collected from across the United States. The prevalence of C. difficile spores on hides was 3.2%. C. difficile spores were not detected on preevisceration and postintervention carcasses or in commercially produced ground beef. Phenotypic and genetic characterizations were carried out for all 18 isolates collected from hide samples. Twenty-two percent of the isolates were nontoxigenic strains, while 78% of the isolates were toxigenic. Toxinotyping and PCR ribotyping patterns revealed that 6 and 33% of the isolates were identified as NAP1 and NAP7 strains, respectively. This article evidences that the prevalence of C. difficile , specifically pathogenic strains, in the U.S. beef production chain is low.

Although numerous antimicrobial interventions targeting Escherichia coli O157:H7 have been developed and implemented to decontaminate meat and meat products during the harvesting process, the information on efficacy of these interventions against the so-called Big Six non-O157 Shiga toxin–producing E. coli (STEC) strains is limited. Prerigor beef flanks (160) were inoculated to determine if antimicrobial interventions currently used by the meat industry have a similar effect in reducing non-O157 STEC serogroups O26, O45, O103, O111, O121, and O145 compared with E. coli O157:H7. A high (10 4 CFU/cm 2 ) or a low (10 1 CFU/cm 2 ) inoculation of two cocktail mixtures was applied to surfaces of fresh beef. Cocktail mixture 1 was composed of O26, O103, O111, O145, and O157, while cocktail mixture 2 was composed of O45, O121, and O157. The inoculated fresh beef flanks were subjected to spray treatments by the following four antimicrobial compounds: acidified sodium chlorite, peroxyacetic acid, lactic acid, and hot water. High-level inoculation samples were enumerated for the remaining bacteria populations after each treatment and compared with the untreated controls, while low-level inoculation samples were chilled for 48 h at 4°C before enrichment, immunomagnetic separation, and isolation. Spray treatments with hot water were the most effective, resulting in mean pathogen reductions of 3.2 to 4.2 log CFU/cm 2 , followed by lactic acid. Hot water and lactic acid also were the most effective interventions with the low-level inoculation on surfaces of fresh beef flanks after chilling. Peroxyacetic acid had an intermediate effect, while acidified sodium chlorite was the least effective in reducing STEC levels immediately after treatment. Results indicate that the reduction of non-O157 STEC by antimicrobial interventions on fresh beef surfaces were at least as great as for E. coli O157:H7. However, the recovery of these low inoculation levels of pathogens indicated that there is no single intervention to eliminate them.

Bovine peripheral lymph nodes (LNs) have been identified as a potential source of Salmonella when trim containing these nodes is incorporated into ground beef. Studies examining the prevalence of Salmonella in peripheral LNs of cattle are few in number, and the microbiological methods used for these analyses have not been validated. Given that Salmonella contamination may be found on postintervention carcasses, it is important to understand the extent to which Salmonella contamination from surrounding adipose tissue is transferred to LN samples during sample preparation. To better understand the potential for cross-contamination, 906 LN samples were collected from postintervention carcasses and these, along with the corresponding adipose trim (AT), were analyzed for the presence of Salmonella . The results showed that the Salmonella prevalence in LNs and on AT was 0.8 and 5%, respectively, but that it was possible to find AT positive for Salmonella contamination while the corresponding LNs were negative and vice versa. In order to examine the dynamics of cross-contamination between surface adipose tissue and LNs in the trimming process, inoculation studies were performed. The efficacy of LN submersion in boiling water as a means of surface sterilization and the effect of boiling on the viability of Salmonella contained within LN samples were also examined. The results showed that, on average, 23 to 43% of the inoculated LN samples in this study were cross-contaminated by Salmonella on surrounding adipose tissue when present in the range of 10 1 to 10 2 CFU per sample; however, surface decontamination methods were very effective at removing Salmonella cross-contaminants in this range.

Currently used industry testing programs require the ability to detect Escherichia coli O157:H7 in samples of beef trim or ground beef at levels as low as 1 CFU/375 g. We present a reliable protocol for generating a control inoculum for verification testing at this low concentration and evaluate its use. Results show that half of all samples received no cells when 1 CFU was the target concentration and that targets greater than 3 CFU were much more reliable. Detection by culture isolation and two commercial assays, Qualicon BAX-MP and BioControl GDS, detected 94% ± 11%, 92% ± 10%, and 92% ± 7% of samples inoculated with 5.4 CFU (range 1 to 9 CFU), respectively. We also examined the effect of background aerobic plate count (APC) bacteria and fat content effects on the detection of E. coli O157:H7. At APC concentrations below 6 log CFU/g, the rapid methods detected all beef trim samples inoculated with 26 CFU of E. coli O157:H7 per 65 g. At an APC of 6.7 log CFU/g, culture, BAX-MP, and GDS detected 100, 75, and 13%, respectively, of inoculated samples. Neither commercial method detected E. coli O157:H7 in the samples when APC was 7.7 log CFU/g, whereas culture was able to detect 63% of E. coli O157:H7 in the samples when APC was at this concentration. Increased fat content correlated with decreasing recovery of immunomagnetic separation beads, but this was not observed to interfere with detection of E. coli O157:H7.

Direct-fed microbials (DFM) have been identified as potential preharvest interventions for the reduction of foodborne bacterial pathogens such as Escherichia coli O157:H7. This study evaluated the efficacy of a DFM consisting of Bacillus subtilis strain 166 as an antimicrobial intervention strategy for the reduction of prevalence and load of E. coli O157:H7 in feces and on hides of feedlot cattle. Cattle ( n = 526) were divided among 16 feedlot pens. Half of the pens received the DFM, and the other half did not. Hide and fecal samples were collected from each animal on days 28, 63, and 84 of the feeding trial. Over the course of the 84-day feeding period, there were no significant differences observed between treatments for either hide or fecal prevalence of E. coli O157:H7, or for the percentage of animals that were shedding E. coli O157:H7 at high levels (≥200 CFU/g) in their feces or harboring E. coli O157:H7 at high levels (≥40 CFU/cm 2 ) on their hides. In addition, there was no significant difference between the average daily gains for the treated and control groups, with both groups averaging 1.3 kg/day. We concluded that the DFM tested would not be an effective preharvest intervention against E. coli O157:H7.

The prevalence rates of Escherichia coli O157:H7 and Salmonella at different sampling sites on cattle hides were determined at a feedlot and a processing plant. Sponge samples were collected from six hide surface sites at the feedlot (left and right shoulders, left and right ribs, back, and belly) and four sites at the processing plant (left and right shoulders, back, and belly). The prevalence of E. coli O157:H7 was approximately 80% for left and right shoulder and rib samples, 68% for back samples, and 92% for belly samples collected at the feedlot. At the processing plant, the prevalences of E. coli O157:H7 at all four sites were between 76 and 79%. Salmonella prevalence in feedlot samples was too low to allow for accurate analysis. The prevalence of Salmonella at processing was 49% for left shoulder samples, 48% for right shoulder samples, 40% for back samples, and 68% for belly samples. The results of this study indicate that the site most likely to be naturally contaminated with E. coli O157:H7 and Salmonella simultaneously was the belly.

1,3-Dibromo-5,5-dimethylhydantoin (DBDMH; 25°C) and hot water (85°C) spray treatments were evaluated for efficacy in decontamination of pathogenic bacteria attached to beef carcass surfaces represented by cutaneous trunci (CT) muscle sections and beef hearts. Treatments were evaluated using two different systems, a commercial carcass wash cabinet and a model carcass washer. The effects were measured immediately after treatment and again after 48 h of storage at 4°C. Sections of CT and beef hearts were inoculated with bovine fecal solution containing approximately 6 log CFU/cm 2 of Escherichia coli O157:H7 and Salmonella . After DBDMH or hot water spray treatments, bacterial populations were enumerated immediately and after storage for 48 h at 4°C. DBDMH treatments reduced aerobic plate counts, Enterobacteriaceae , E. coli O157: H7, and Salmonella by the same or slightly lower amounts relative to hot water treatment. DBDMH reduced aerobic plate counts and Enterobacteriaceae by 2.8 to 3.6 log CFU/cm 2 , E. coli O157:H7 by 1.6 to 2.1 log CFU/cm 2 , and Salmonella by 0.7 to 2.3 log CFU/cm 2 on CT sections and beef hearts. Hot water treatment reduced aerobic plate counts and Enterobacteriaceae by 3.0 to 4.1 log CFU/cm 2 , E. coli O157:H7 by 1.8 to 2.3 log CFU/cm 2 , and Salmonella by 2.5 to 2.8 log CFU/cm 2 . After 48 h of storage, the reductions of organisms by DBDMH and hot water treatments were not different. This study demonstrated that DBDMH spray washing could be effective as an antimicrobial intervention for beef carcasses and variety meats.

Several strains of Salmonella have been identified as resistant to multiple antibiotics. What is not known is whether strains possessing multidrug resistance properties also have the ability to resist the killing effects of the antimicrobial interventions used in beef processing. The research project described herein was designed to determine whether antimicrobial interventions currently in place in beef processing facilities are adequate for reducing the foodborne pathogen loads on beef carcass surfaces contaminated with multidrug-resistant (MDR) Salmonella . The data presented here indicate that MDR Salmonella is reduced at least as effectively as are Escherichia coli O157:H7 and susceptible Salmonella when treated with antimicrobial interventions currently in use at most U.S. beef processing plants. The E. coli O157:H7 strains used in this study were divided into two groups, strains that have a genetic polymorphism associated with human disease and strains not typically found to cause human disease. No differences were detected in the abilities of these two strain types to survive antimicrobial interventions. These results indicate that neither the drug resistance status of a particular Salmonella strain nor the likelihood that a particular E. coli O157:H7 strain will cause human illness influences the antimicrobial efficacy of the interventions utilized by the modern beef processing plants.

Transportation from the feedlot and lairage at the processing plant have been identified as potential sources of Escherichia coli O157:H7 and Salmonella hide contamination. The objective of this study was to perform a comprehensive tracking analysis of E. coli O157:H7 and Salmonella associated with beef cattle from the feedlot through processing. Cattle ( n = 581) were sampled in a feedlot, then transported in multiple lots to three commercial, fed beef processing plants in the United States, where they were sampled again. Samples were collected from the tractor trailers prior to loading cattle and from the lairage environment spaces prior to entry of the study cattle. Pathogen prevalence on cattle hides increased on every lot of cattle between exiting the feedlot and beginning processing. Prior to loading cattle, E. coli O157:H7 was found in 9 (64%) of 14 tractor trailers. E. coli O157:H7 was detected in over 60% of the samples from each lairage environment area, while Salmonella was detected in over 70% of the samples from each lairage environment area. E. coli O157:H7 and Salmonella isolates ( n 3,645) were analyzed using pulsed-field gel electrophoresis. The results of the pulsed-field gel electrophoresis tracking indicate that the transfer of bacteria onto cattle hides that occurs in the lairage environments of U.S beef processing plants accounts for a larger proportion of the hide and carcass contamination than does the initial bacterial population found on the cattle exiting the feedlot. Finally, the results of this study indicate that hide wash cabinets are effective in removing contamination derived from the lairage environment.

A potential source of pathogenic bacteria in ground beef is the lymphatic system, specifically the lymph nodes. Bacteria have been isolated from the lymph nodes of cattle at slaughter; however, most studies have dealt with mesenteric lymph nodes, which are not normally incorporated into ground beef. The objective of the current study was to determine the prevalence and multidrug-resistance status of Salmonella in bovine lymph nodes associated with lean and fat trimmings that might be utilized in ground beef production. Bovine lymph nodes ( n = 1,140) were collected from commercial beef processing plants. Half of the lymph nodes sampled were obtained from cull cow and bull processing plants, and the remainder were obtained from fed beef processing plants. Lymph nodes located in chuck and flank adipose tissue were collected for this study. Salmonella prevalence in the lymph node samples was low, with an overall prevalence of 1.6% and a 95% confidence interval of 0.85 to 2.3%. Lymph nodes from cull cattle carcasses had a higher prevalence of Salmonella than did those from fed cattle carcasses. Lymph nodes from the flanks of cow and bull carcasses had the highest prevalence at 3.86%, whereas lymph nodes from the chuck region of fed cattle carcasses had the lowest prevalence at 0.35%. Three of the 18 Salmonella -positive lymph node samples contained multidrug-resistant Salmonella , and all 3 samples were from cull cattle.

Listeria monocytogenes , the causative agent of epidemic and sporadic listeriosis, is routinely isolated from many sources, including cattle, yet information on the prevalence of Listeria in beef processing plants in the United States is minimal. From July 2005 through April 2006, four commercial cow and bull processing plants were sampled in the United States to determine the prevalence of Listeria and the serovar diversity of L. monocytogenes . Samples were collected during the summer, fall, winter, and spring. Listeria prevalence on hides was consistently higher during cooler weather (28 to 92% of samples) than during warmer weather (6 and 77% of samples). The Listeria prevalence data collected from preevisceration carcass ranged from undetectable in some warm season samples to as high as 71% during cooler weather. Listeria on postintervention carcasses in the chill cooler was normally undetectable, with the exception of summer and spring samples from one plant where >19% of the carcasses were positive for Listeria . On hides, L. monocytogenes serovar 1/2a was the predominant serovar observed, with serovars 1/2b and 4b present 2.5 times less often and serovar 1/2c not detected on any hides sampled. L. monocytogenes serovars 1/2a, 1/2c, and 4b were found on postintervention carcasses. This prevalence study demonstrates that Listeria species are more prevalent on hides during the winter and spring and that interventions being used in cow and bull processing plants appear to be effective in reducing or eliminating Listeria contamination on carcasses.

Although the United States produces 203 million lb (ca. 92.1 kg) of domestic lamb and mutton each year, thorough studies of the microbiological safety during lamb processing are lacking. To address this missing information, a total of 2,548 sponge samples from pelts, preevisceration carcasses, and postintervention carcasses were collected from multiple large commercial lamb processing plants to determine aerobic plate counts, the prevalences of Escherichia coli O157:H7, non-O157 Shiga toxin–producing E. coli (STEC), and Salmonella . The averages of the aerobic plate counts from pelts, the preevisceration carcasses, and the postintervention carcasses were 6.3, 4.4, and 2.4 log CFU/100 cm 2 , respectively. The prevalences of E. coli O157:H7 from the pelts, the preevisceration carcasses, and the postintervention carcasses were 12.8, 1.6, and 2.9%, respectively. The average Salmonella prevalences were 14.4, 4.3, and 1.8% for pelts, preevisceration carcasses, and postintervention carcasses, respectively. The most frequently identified Salmonella serotype was Heidelberg. The prevalences of non-O157 STEC from pelts, preevisceration carcasses, and postintervention carcasses averaged 86.2, 78.6, and 81.6%, respectively. A total of 488 non-O157 STEC strains were isolated from postintervention carcasses. Sixty-nine different serotypes of non-O157 STEC were identified. The most frequently detected serotypes were O91:H14 (40.8%), followed by O5:H19 (18.4%). A small number of STEC serotypes associated with severe human illness were isolated from postintervention carcasses. These were serotypes O76:H19, O128:H2 (0.8%), O146:H8 (2.1%), O146:H21, O163:H19, and O174:H8 (1.3%). The results of this study establish a baseline for microbiological quality and prevalences of Salmonella , E. coli O157:H7, and STEC in U.S. lamb processing plants.

Cattle hides become contaminated with Escherichia coli O157:H7 via pathogen transmission in the feedlot, during transport, and while in the lairage environment at the processing facility, and the bacteria can be transferred to beef carcasses during processing. Several studies have shown that E. coli O157:H7 strains possessing indistinguishable restriction digest patterns (RDPs) can be isolated from distant locations. Most of these studies, however, examined RDPs from strains isolated within a single region of the United States or Canada. The experiment described in the present study was designed to identify the molecular genotypes of E. coli O157:H7 isolates from beef cattle hides in nine major cattle-producing regions of North America. Prevalence for E. coli O157:H7 in beef cattle hide samples ranged from 9 to 85%. Pulsed-field gel electrophoresis (PFGE) analysis of Xba I-digested genomic DNA from 1,193 E. coli O157:H7 isolates resulted in 277 unique RDPs. Of the 277 unique Xba I RDPs, 54 contained isolates collected from multiple regions. After two subsequent rounds of PFGE analysis ( Bln I and Spe I), there were still many isolates ( n = 154) that could not be distinguished from others, even though they were collected from different regions separated by large geographical distances. On multiple occasions, strains isolated from cattle hides in Canada had RDPs that were indistinguishable after three enzyme digestions from cattle hide isolates collected in Kansas and Nebraska. This information clearly shows that strains with indistinguishable RDPs originate from multiple sources that can be separated by large distances and that this should be taken into account when the source tracking of isolates is based on PFGE.

Harborage of Escherichia coli O157:H7 and Salmonella on animal hides at slaughter is the main source of beef carcass contamination during processing. Given this finding, interventions have been designed and implemented to target the hides of cattle following entry into beef processing plants. Previous interventions targeting hides have not been suitable for all beef processing plants because of cost and space restrictions. In this study, a hide wash cabinet was evaluated to determine whether it was more amenable to widespread use in the beef processing industry, especially for small and medium-size plants. Overall, 101 (35.1%) of 288 beef cattle hides sampled before entry into the hide wash cabinet harbored E. coli O157:H7 at or above the limit of detection (40 CFU/100 cm 2 ). After passage through the hide wash cabinet, only 38 (13.2%) of 288 hides had E. coli O157:H7 levels ≥40 CFU/100 cm 2 . Before the hide wash cabinet, 50 (17%) of 288 hides harbored E. coli O157:H7 at levels above 100 CFU/100 cm 2 , with one sample as high as 20,000 CFU/100 cm 2 . In contrast, only 14 (5%) of 288 hides had E. coli O157:H7 levels above 100 CFU/100 cm 2 after hide washing, with the highest being 2,000 CFU/100 cm 2 . These same trends also were found for Salmonella before and after hide washing. These results indicate that the hide wash cabinet described in this study was effective and should provide small and medium-size processing plants with an affordable hide wash intervention strategy.

Hide has been established as the main source of carcass contamination during cattle processing; therefore, it is crucial to minimize the amount of Escherichia coli O157:H7 on cattle hides before slaughter. Several potential sources of E. coli O157: H7 are encountered during transportation and in the lairage environment at beef-processing facilities that could increase the prevalence and numbers of E. coli O157:H7 on the hides of cattle. On three separate occasions, samples were obtained from cattle at the feedlot and again after cattle were stunned and exsanguinated at the processing plant (286 total animals). The prevalence of E. coli O157:H7 on hides increased from 50.3 to 94.4% between the time cattle were loaded onto tractor-trailers at the feedlot and the time hides were removed in the processing plant. Before transport, nine animals had E. coli O157:H7 in high numbers (>0.4 CFU/cm 2 ) on their hides. When sampled at the slaughter facility, the number of animals with high hide numbers had increased to 70. Overall, only 29% of the E. coli O157:H7 isolates collected postharvest (221 of 764) matched pulsed-field gel electrophoresis types collected before transport. The results of this study indicate that transport to and lairage at processing plants can lead to increases in the prevalence and degree of E. coli O157:H7 contamination on hides and the number of E. coli O157:H7 pulsed-field gel electrophoresis types associated with the animals. More study is needed to confirm the mechanism by which additional E. coli O157:H7 strains contaminate cattle hides during transport and lairage and to design interventions to prevent this contamination.

Since the mid-1990s, the beef industry has used a process called test and hold, wherein beef trim and ground beef are tested to keep products contaminated with Escherichia coli O157:H7 out of commerce. Current O157:H7 detection methods rely on a threshold level of bacterial growth for detection, which is dependent on the growth medium used. Twelve media were examined for growth and doubling time: buffered peptone water (BPW), SOC (which contains tryptone, yeast extract, KCl, MgCl 2 , and glucose), buffered peptone water plus SOC (BPW-SOC), Bacto-NZYM, RapidChek E. coli O157:H7 medium, BioControl EHEC8 culture medium, Neogen Reveal for E. coli O157:H7—Eight Hour medium (Neogen Reveal 8), BAX System medium for E. coli O157:H7 (BAX), BAX System medium for E. coli O157:H7 MP (BAX-MP), modified E. coli broth, nutrient medium, and tryptic soy broth (TSB). All media were tested at 37 or 42°C under static or shaking conditions. The eight media with the highest total CFU per milliliter and most rapid doubling times were BPW-SOC, NZYM, RapidChek, EHEC8, Neogen Reveal 8, BAX, BAX-MP, and TSB. The ability of these eight media to enrich E. coli O157:H7 in ground beef was further evaluated through time-course experiments using immunomagnetic separation. Of these media, TSB was the easiest to prepare, had a wide application base, and was the least expensive. In the test-and-hold process, the normal ratio of medium to product is 1:10. In this study, a 1:3 ratio worked as well as a 1:10 ratio. Processors using test-and-hold procedures could use 1 liter of TSB to enrich for E. coli O157:H7 in a 375-g sample instead of the usual 3.375 liters, thus saving reagents, time, and labor while maintaining accuracy.

The Meats Research Unit (MRU) methods, developed by MRU scientists of the U.S. Meat Animal Research Center, have been used to study the prevalence of Escherichia coli O157:H7 in cattle carcass, hide, and fecal samples. The sensitivity of these methods for recovery of injured E. coli O157:H7 cells from inoculated and uninoculated samples was determined, and potential improvements to these methods were evaluated. When using the conventional MRU methods, 91% of the pre-evisceration carcass samples tested positive for E. coli O157:H7 when inoculated with 5 to 10 CFU, 100% of hide samples tested positive for E. coli O157:H7 when inoculated with 30 to 50 CFU, and 96% of the fecal samples produced positive results when inoculated with 300 to 400 CFU per 10 g. The addition of a phosphate buffer to the tryptic soy broth enrichment improved recovery of E. coli O157:H7 from feces. Using the modified enrichment, 92% of the samples were identified as positive when inoculated with 10 to 30 CFU per 10 g. Substituting a commercially available wash buffer for the phosphate-buffered saline (PBS) plus Tween 20 wash buffer during immunomagnetic separation of hide samples improved recovery of the target organism at lower inoculum concentrations. When comparing uninoculated samples, substituting a PBS buffer plus a zwitterionic detergent for PBS plus Tween 20 also had a positive effect on recovery of E. coli O157:H7 from hide samples. Data presented here indicate that the MRU methods are highly effective at recovering injured E. coli O157:H7 from fecal, hide, and beef carcass samples; however, modifications can be added to increase the sensitivity.

The hides of cattle are the primary source of pathogens such as Escherichia coli O157:H7 that contaminate preevisceration carcasses during commercial beef processing. A number of interventions that reduce hide contamination and subsequent carcass contamination are currently being developed. The objective of this study was to determine the efficacy of ozonated and electrolyzed oxidizing (EO) waters to decontaminate beef hides and to compare these treatments with similar washing in water without the active antimicrobial compounds. Cattle hides draped over barrels were used as the model system. Ozonated water (2 ppm) was applied at 4,800 kPa (700 lb in 2 ) and 15°C for 10 s. Alkaline EO water and acidic EO water were sequentially applied at 60°C for 10 s at 4,800 and 1,700 kPa (250 lb in 2 ), respectively. Treatment using ozonated water reduced hide aerobic plate counts by 2.1 log CFU/100 cm 2 and reduced Enterobacteriaceae counts by 3.4 log CFU/100 cm 2 . EO water treatment reduced aerobic plate counts by 3.5 log CFU/100 cm 2 and reduced Enterobacteriaceae counts by 4.3 log CFU/100 cm 2 . Water controls that matched the wash conditions of the ozonated and EO treatments reduced aerobic plate counts by only 0.5 and 1.0 log CFU/100 cm 2 , respectively, and each reduced Enterobacteriaceae counts by 0.9 log CFU/100 cm 2 . The prevalence of E. coli O157 on hides was reduced from 89 to 31% following treatment with ozonated water and from 82 to 35% following EO water treatment. Control wash treatments had no significant effect on the prevalence of E. coli O157:H7. These results demonstrate that ozonated and EO waters can be used to decontaminate hides during processing and may be viable treatments for significantly reducing pathogen loads on beef hides, thereby reducing pathogens on beef carcasses.

Low-dose, low-penetration electron beam (E-beam) irradiation was evaluated for potential use as an antimicrobial intervention on beef carcasses during processing. The objectives of this study were (i) to assess the efficacy of E-beam irradiation to reduce concentrations of Escherichia coli O157:H7 on a large beef surface and (ii) to evaluate the effect of the treatment on the sensory properties of the product. A 1-kGy dose of E-beam radiation reduced E. coli O157:H7 inoculated onto sections of cutaneous trunci at least 4 log CFU/cm 2 . In assessing organoleptic impact, flank steak was used as the model muscle. Flank steaks with various levels of penetration by radiation (5, 10, 25, 50, and 75%) were evaluated. None of the flank steak sensory attributes were affected ( P > 0.05) by any penetration treatment. Ground beef formulations consisting of 100, 50, 25, 10, 5, and 0% surface-irradiated beef were tested. A trained sensory panel did not detect any difference between the control (0%) and either the 5 or 10% treatments. These results suggest that if chilled carcasses were subjected to low-dose E-beam irradiation, aroma and flavor of ground beef would not be impacted. The data presented here indicate that low-dose, low-penetration E-beam irradiation has potential use as an antimicrobial intervention on beef carcasses during processing and minimally impacts the organoleptic qualities of the treated beef products.