Pulsed field gel electrophoresis of related Escherichia coli O157 isolates associated with beef cattle and comparison with unrelated isolates from animals, meats and humans

The pulsed field gel electrophoresis (PFGE) diversity of 51 related Escherichia coli O157 isolates, associated with beef cattle from a single-farm-to-single abattoir (SF-SA) chain of events was determined. The 51 related E. coli O157 isolates from hides, faeces or carcasses of SF-SA cattle produced 11 different PFGE profiles. Also, the PFGE diversity of 6 isolates, associated with a second cattle abattoir, was determined; only two PFGE profiles were found. On the other hand, the PFGE diversity of 136 unrelated E. coli O157 isolates (from healthy meat animals, retail meats and cases of human disease) was also determined. The 136 unrelated E. coli O157 isolates produced 78 different PFGE profiles, most of which (approximately 70%) comprised only one isolate. Overall, the results showed: (a) related E. coli O157 isolates (from both SF-SA events, and the second abattoir) had a markedly narrower clonal profile than the 136 unrelated E. coli O157 isolates; (b) the isolation of identical PFGE types from hide, lairage environment, and carcasses confirms the significance of cross-contamination (both pre-slaughter and during skinning) taking place at abattoirs; and (c) PFGE typing of isolates offers a good tool for tracking sources/routes of such cross-contamination. Such cross-contamination may lead to originally E. coli O157-free animals (and resultant carcasses) becoming contaminated during farm-slaughter-dressing chain of events, so development of efficient control strategies is required.     

Escherichia coli O157 prevalence and enumeration of aerobic bacteria, Enterobacteriaceae, and Escherichia coli O157 at various steps in commercial beef processing plants

The effectiveness of current antimicrobial interventions used in reducing the prevalence or load of Escherichia coli O157 and indicator organisms on cattle hides and carcasses at two commercial beef processing plants was evaluated. Sponge sampling of beef cattle was performed at five locations from the initial entry of the animals to the slaughter floor to the exit of carcasses from the "hotbox" cooler. For each sample, E. coli O157 prevalence was determined and total aerobic bacteria, Enterobacteriaceae, and E. coli O157 were enumerated. E. coli O157 was found on 76% of animal hides coming into the plants, but no carcasses leaving the cooler were identified as contaminated with E. coli O157. A positive relationship was seen between the incidence of E. coli O157 in hide samples and that in preevisceration samples. Aerobic plate counts and Enterobacteriaceae counts averaged 7.8 and 6.2 log CFU/100 cm2, respectively, on hides, and 1.4 and 0.4 log CFU/100 cm2, respectively, on chilled carcasses. Aerobic plate counts and Enterobacteriaceae counts on preevisceration carcasses were significantly related to the respective levels on the corresponding hides; the carcasses of animals whose hides carried higher numbers of bacteria were more likely to carry higher numbers of bacteria. Implementation of the sampling protocol described here would allow processors to evaluate the efficacy of on-line antimicrobial interventions and allow industrywide benchmarking of hygienic practices.     

An investigation of Escherichia coli O157 contamination of cattle during slaughter at an abattoir

The extent of contamination with Escherichia coli O157 was determined for 100 cattle during slaughter. Samples from 25 consecutively slaughtered cattle from four unrelated groups were collected from the oral cavity, hide, rumen, feces after evisceration, and pre- and postchill carcass. Ten random fecal samples were collected from the pen where each group of animals was held at the abattoir. E. coli O157 was detected using automated immunomagnetic separation (AIMS), and cell counts were determined using a combination of most probable number (MPN) and AIMS. E. coli O157 was isolated from 87 (14%) of the 606 samples collected, including 24% of 99 oral cavity samples, 44% of 100 hides, 10% of 68 fecal samples collected postevisceration, 6% of 100 prechill carcass swabs, and 15% of 40 fecal samples collected from holding pens. E. coli O157 was not isolated from rumen or postchill carcass samples. E. coli O157 was isolated from at least one sample from each group of cattle tested, and the prevalence in different groups ranged from less than 1 to 41%. The numbers of E. coli O157 differed among the animals groups. The group which contained the highest fecal (7.5 x 10(5) MPN/g) and hide (22 MPN/cm2) counts in any individual animal was the only group in which E. coli O157 was isolated from carcasses, suggesting a link between the numbers of E. coli O157 present and the risk of carcass contamination. Processing practices at this abattoir were adequate for minimizing contamination of carcasses, even when animals were heavily contaminated with E. coli O157.     

Transportation and lairage environment effects on prevalence, numbers, and diversity of Escherichia coli O157:H7 on hides and carcasses of beef cattle at processing

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/cm2) 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.     

Pulsed-field gel electrophoresis characterization of Shiga toxin-producing Escherichia coli O157 from hides of cattle at slaughter

Contamination of the brisket areas of the hides of healthy adult cattle with Shiga toxin-producing Escherichia coli O157 at slaughter in England was studied. In total, 73 cattle consignments comprising 584 animals delivered to one abattoir over 3 days during 1 week in July 2001 were studied: 26 cattle consignments arriving on Monday, 32 consignments arriving on Wednesday, and 15 consignments arriving on Friday. Consignment sizes ranged from 1 to 23 animals, with a mean consignment size of 8. The hide of the first animal to be slaughtered in each consignment was sampled by using a sponge swab moistened with 0.85% saline to rub an unmeasured brisket (ventral) area (ca. 30 by 30 cm). The process of isolating E. coli O157 from the swabs consisted of enrichment, screening with immunoprecipitation assay kits, and immunomagnetic separation. E. coli O157 was found on 24 of 73 (32.9%) cattle hides examined, and 21 of these 24 isolates produced Shiga toxins. The 24 E. coli O157 isolates produced six different pulsed-field gel electrophoresis profiles, and 18 (75%) of the isolates were of one prevalent clone. The high prevalence of one E. coli O157 clone on the hides of cattle at slaughter could be due to a high prevalence of that clone on the 18 farms involved (not investigated in the current study), in the postfarm transport or lairage environments, or both. Since the lairage environment, but not the farm of origin or the postfarm transport vehicle, was a factor common to all 18 cattle consignments, it could have played an important role in spreading the prevalent E. coli O157 clone to the cattle hides. Lairage pen floors and the stunning box floor were identified as the most probable sites along the unloading-to-slaughter route at which the brisket areas of cattle hides could become contaminated.     

Comparison of the molecular genotypes of Escherichia coli O157:H7 from the hides of beef cattle in different regions of North America

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 XbaI-digested genomic DNA from 1,193 E. coli O157:H7 isolates resulted in 277 unique RDPs. Of the 277 unique XbaI RDPs, 54 contained isolates collected from multiple regions. After two subsequent rounds of PFGE analysis (BlnI and SpeI), 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.     

Effect of chemical dehairing on the prevalence of Escherichia coli O157:H7 and the levels of aerobic bacteria and enterobacteriaceae on carcasses in a commercial beef processing plant

The objective of this experiment was to test the hypothesis that cleaning cattle hides by removing hair and extraneous matter before hide removal would result in improved microbiological quality of carcasses in commercial beef processing plants. To test this hypothesis, we examined the effect of chemical dehairing of cattle hides on the prevalence of Escherichia coli O157:H7 and the levels of aerobic bacteria and Enterobacteriaceae on carcasses. Samples from 240 control (conventionally processed) and 240 treated (chemically dehaired before hide removal) hides (immediately after stunning but before treatment) and preevisceration carcasses (immediately after hide removal) were obtained from four visits to a commercial beef processing plant. Total aerobic plate counts (APC) and Enterobacteriaceae counts (EBC) were not (P > 0.05) different between cattle designated for chemical dehairing (8.1 and 5.9 log CFU/100 cm2 for APC and EBC, respectively) and cattle designated for conventional processing (8.0 and 5.7 log CFU/100 cm2 for APC and EBC, respectively). However, E. coli O157:H7 hide prevalence was higher (P < 0.05) for the control group than for the treated group (67% versus 88%). In contrast to hides, the bacterial levels were lower (P < 0.05) on the treated (3.5 and 1.4 log CFU/100 cm2 for APC and EBC) than the control (5.5 and 3.2 log CFU/100 cm2 for APC and EBC) preevisceration carcasses. Prevalence of E. coli O157:H7 was lower (P > 0.05) on treated than on control preevisceration carcasses (1% versus 50%). These data indicate that chemical dehairing of cattle hides is an effective intervention to reduce the incidence of hide-to-carcass contamination with pathogens. The data also imply that any effective hide intervention process incorporated into beef processing procedures would significantly reduce carcass contamination by E. coli O157:H7.     

Contamination of bovine carcasses and abattoir environment by Escherichia coli O157:H7 in Istanbul

The aim of this study was to investigate contamination of carcasses and abattoir environment with Escherichia coli O157:H7. Five abattoirs in Istanbul were visited between January 2000 and April 2001. During visits, sampling was performed and a total of 330 cattle were selected. Cattle were examined for the presence of faeces on the hide (abdomen and legs) before slaughter. The swabs from the carcasses and environmental samples (abattoir floor, benches including conveyors, knives, aprons, saws, hooks, hands) were taken at the abattoir immediately after slaughter using sterile cotton swabs. A sample from the wash water of the abattoir was also taken. Preenrichment, immunomagnetic separation and CT-SMAC agar were used for the isolation. The reaction of the isolates with anti-O157 and H7 antisera were also analysed. Twelve strains (3.6%) of E. coli O157 were isolated from the cattle carcasses and eight (2.4%) of them gave positive reaction with anti-H:7. Six strains of E. coli O157 were isolated from the environmental samples and all strains were positive for H7. The number of E. coli O157H:7 strains isolated from the environmental samples was two from the knife, two from the hands, one from the apron and one from the floor. No E. coli O157 was isolated from the abattoir water.     

Faecal carriage of Verocytotoxin-producing Escherichia coli O157 and carcass contamination in cattle at slaughter in northern Italy.

A study on the prevalence of the faecal carriage of Verocytotoxin (VT)-producing Escherichia coli (VTEC) O157 and on the rate of carcass contamination was carried out on feedlot cattle and dairy cows at slaughter in northern Italy. Between April 1998 and January 1999, 12 sampling visits were performed on different days in seven different slaughterhouses. At each visit, 5-12 animals consecutively slaughtered were selected. From each animal, faeces were collected from the rectum immediately after slaughter and surface swabs were taken from the leg region and the diaphragmatic insertion of the carcass. All samples were examined for the presence of VTEC O157 using an immunomagnetic separation technique. A total of 100 animals coming from 60 different farms were examined. In total, VTEC O157 was isolated from the intestinal content of 17, and from the carcasses of 12 of the 100 animals examined. In particular, VTEC O157 was recovered from six (35.3%) out of the 17 carcasses from which the organism had previously been isolated from rectal content and from six (7.3%) of the 82 carcasses of the stool-negative cattle. In seven carcasses, VTEC O157 was isolated from the leg area, in two carcasses from the diaphragmatic area, and in three carcasses from both areas. Major differences in the prevalence of VTEC O157 were observed in the different groups of cattle sampled. In 7 of the 12 sampling visits, all the specimens examined were negative, while 16 of the 17 positive stool samples and 11 of the 12 positive carcass swabs were collected during three of the visits, performed in June in three different abattoirs. In these three visits, the ratios between the percentage of animals carrying VTEC O157 in the stools and the percentage of contaminated carcasses were 0.33, 0.57, and 1.66, respectively; thus, confirming that slaughter practices can largely influence the rate of carcass contamination. Phage typing and PFGE analysis of VTEC O157 isolated from samples collected at the same visit suggested that both auto- and cross-contamination occurred.     

Prevalence of Escherichia coli O157 and levels of aerobic bacteria and Enterobacteriaceae are reduced when hides are washed and treated with cetylpyridinium chloride at a commercial beef processing plant

The objective of this experiment was to test the potential of a combined water wash and cetylpyridinium chloride (CPC) treatment as a hide intervention applied to cattle in the holding pens of a processing plant immediately before stunning. Over 2 processing days, 149 control and 139 treated cattle were tested. Control cattle were processed in the normal manner. The treatment group was prewashed with water the day before harvest. Immediately before stunning, these cattle were sprayed twice with 1% CPC, first for 3 min, then for 1 min. Hides and preevisceration carcasses were sampled to determine aerobic plate counts, Enterobacteriaceae counts (EBC), and Escherichia coli O157 prevalence. The treatment reduced the prevalence of E. coli O157 on hides from 56% to 34% and the prevalence on preevisceration carcasses from 23% to 3%. The treatment decreased aerobic plate counts from 4.9 log CFU/100 cm2 to 3.4 log CFU/100 cm2 and EBC from 3.1 log CFU/100 cm2 to 2.0 log CFU/100 cm2 on preevisceration carcasses. The treatment of hides did not result in any detectable CPC contamination of the chilled carcasses. These data indicated that a 1% CPC treatment preceded by a water wash was capable of reducing hide prevalence of E. coli O157 from as high as 80% to less than 50%, resulting in preevisceration carcass prevalence of 5% or less. We conclude that water washing followed by an antimicrobial treatment, such as CPC, has great potential as an effective hide intervention step and should be further evaluated for implementation as a processing step after stunning and before hide removal.     

Effects of a minimal hide wash cabinet on the levels and prevalence of Escherichia coli O157:H7 and Salmonella on the hides of beef cattle at slaughter

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 cm2). After passage through the hide wash cabinet, only 38 (13.2%) of 288 hides had E. coli O157:H7 levels > or =40 CFU/100 cm2. Before the hide wash cabinet, 50 (17%) of 288 hides harbored E. coli O157:H7 at levels above 100 CFU/100 cm2, with one sample as high as 20,000 CFU/100 cm2. In contrast, only 14 (5%) of 288 hides had E. coli O157:H7 levels above 100 CFU/100 cm2 after hide washing, with the highest being 2000 CFU/100 cm2. 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.     

Comparison of sampling methods for microbiological testing of beef animal rectal/colonal feces, hides, and carcasses

This study compared sampling methods for detecting Escherichia coli O157:H7 and Salmonella in beef cattle feces and on hides and carcasses and for enumerating E. coli biotype I counts (ECC) on carcasses. Fecal samples were collected by rectal/colonal palpation and colonal sponge swabbing. Hides were sampled by sponge swabbing three sites, hair clipping, excision, rinsing, and gauze swabbing, whereas carcasses were sampled by three-site thoracic and pattern-mark sponge swabbing and tissue excision. Overall, irrespective of sampling method, 36.7, 13.3, and 0.0% of lots contained at least one E. coli O157:H7-positive hide, fecal, and carcass sample, respectively, while the corresponding prevalence of Salmonella was 70.0, 16.7, and 6.7%, respectively. For hide sampling, excision and gauze swabbing yielded the fewest (13.3%) E. coli O157:H7-positive samples, while hair clipping and sponge swabbing yielded the most (23.3%). None of the carcass-sampling methods detected E. coli O157:H7 or differed (P > 0.05) in their ability to enumerate ECC. Colonal swabbing was the most effective (10.0%) method for detecting E. coli O157:H7 in feces. No differences (P > 0.05) in Salmonella prevalence were observed between carcass-sampling methods, although three-site sponge swabbing and tissue excision detected the most (3.3%). Hide rinsing was the most effective (P < 0.05) Salmonella detection method (63.3%), but dangers associated with its application may preclude its use by industry; there were no differences (P > 0.05) among other hide-sampling methods. No differences (P > 0.05) in Salmonella detection were observed between fecal-sampling methods. Overall, three-site sponge swabbing was the most feasible and effective sampling method for the detection of E. coli O157:H7 and Salmonella on hides and carcasses.     

Source tracking of Escherichia coli O157:H7 and Salmonella contamination in the lairage environment at commercial U.S. beef processing plants and identification of an effective intervention

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.     

Impact of transportation and lairage on hide contamination with Escherichia coli O157 in finished beef cattle

Transportation of cattle from the feedlot to the slaughter plant could influence hide contamination of Escherichia coli O157. A study was initiated to investigate the influence of transportation and lairage on shedding and hide contamination of E. coli O157. Fecal and hide samples were obtained from 40 pens of harvest-ready beef cattle at the feedlot prior to transport and again at the slaughter plant immediately after slaughter. Potential risk factors for hide contamination at the feedlot, during transport, and at slaughter were evaluated. A multilevel Poisson regression model was used to evaluate if transportation and lairage were associated with hide contamination by E. coli O157 in finished beef cattle. Lots of cattle held in E. coli O157-positive lairage pens had eight times greater risk of having positive slaughter hide samples compared with cattle held in culture-negative pens (relative risk, 8.0; 95% confidence interval, 1.6 to 38.8). Lots of cattle that were held in lairage pens contaminated with feces had three times greater risk for positive slaughter hide samples compared with cattle held in clean pens (relative risk, 3.1; 95% confidence interval, 1.2 to 7.9). Lots of cattle that were transported for long distances (> 160.9 km) had twice the risk of having positive hide samples at slaughter compared with cattle transported a shorter distance (relative risk, 2.4; 95% confidence interval, 1.1 to 5.1). These findings suggest that transportation and lairage should be considered in E. coli O157 control strategies.     

Development and evaluation of an on-line hide decontamination procedure for use in a commercial beef processing plantt

The hides of cattle are the source of Escherichia coli O157:H7 that contaminates beef carcasses during commercial beef processing. Therefore, effective interventions that reduce hide contamination should reduce subsequent carcass contamination. The first objective of this study was to identify the most effective reagents for decontamination of beef hides. Cattle hides draped over barrels were used for in vitro experiments to compare the efficacy of washes using 1.6% sodium hydroxide, 4% trisodium phosphate, 4% chlorofoam, or 4% phosphoric acid, each followed by a rinse step using either water or acidified (pH 7.0) chlorine at 200 or 500 ppm. All treatments using a water rinse reduced hide coliform counts by 1.5 to 2.5 log CFU/ 100 cm2. Compared with water rinses, 200 and 500 ppm acidified chlorine rinses increased efficacy by approximately 1.0 and 2.0 log CFU/100 cm2, respectively. Vacuuming of the treated areas to remove excess liquid improved hide cleanliness by an average of an additional 1.0 log CFU/100 cm2. The second objective was to evaluate the use of an on-line hide-wash cabinet that used a sodium hydroxide wash and a chlorinated (1 ppm) water rinse. Hides sampled before entering and after exiting the cabinet had aerobic plate counts and Enterobacteriaceae counts that were reduced by 2.1 and 3.4 log CFU/100 cm2, respectively, and the prevalence of E. coli O157 on hides was reduced from 44 to 17% when the cabinet was in use. Preevisceration carcass aerobic plate counts and Enterobacteriaceae counts were both reduced by 0.8 log CFU/100 cm2, and the prevalence of E. coli O157 on preevisceration carcasses was reduced from 17 to 2% when the cabinet was in use. These results support decontamination of hides as an effective means to reduce pathogen contamination of cattle carcasses during processing.     

Prevalence of Escherichia coli O157:H7 and performance by beef feedlot cattle given Lactobacillus direct-fed microbials

Fecal shedding of Escherichia coli O157:H7, the prevalence of Escherichia coli O157:H7 in pens and on carcasses and hides, and cattle performance as a result of daily dietary supplementation with Lactobacillus-based direct-fed microbials (DFMs) were evaluated in a feeding trial involving 180 beef steers. Steers were evaluated for shedding of E. coli O157:H7 by an immunomagnetic separation technique on arrival at the feedlot, just before treatment with the DFMs, and every 14 days thereafter until slaughter. Composite pen fecal samples were collected every 14 days (alternating weeks with animal testing), and prevalence on hides and carcasses at slaughter was also evaluated. Feedlot performance (body weight gain and feed intake) was measured for the period during which the DFMs were fed. Gain efficiency was calculated as the ratio of weight gain to feed intake. Lactobacillus acidophilus NPC 747 decreased (P < 0.01) the shedding of E. coli O157:H7 in the feces of individual cattle during the feeding period. E. coli O157:H7 was approximately twice as likely to be detected in control animal samples as in samples from animals receiving L. acidophilus NPC 747. In addition, DFM supplementation decreased (P < 0.05) the number of E. coli O157:H7-positive hide samples at harvest and the number of pens testing positive for the pathogen. Body weight gains (on a live or carcass basis) and feed intakes during the DFM supplementation period did not differ among treatments. Gain efficiencies on a live-weight basis did not differ among treatments, but carcass-based gain/feed ratios tended (P < 0.06) to be better for animals receiving the two DFM treatments than for control animals. The results of this study suggest that the feeding of a Lactobacillus-based DFM to cattle will decrease, but not eliminate, fecal shedding of E. coli O157:H7, as well as contamination on hides, without detrimental effects on performance.     

Studies to evaluate chemicals and conditions with low-pressure applications for reducing microbial counts on cattle hides

Studies were conducted to identify effective antimicrobials and application parameters that could be used as decontamination interventions to reduce microbial loads on cattle hides before removal from carcasses. In study I, hide swatches inoculated with Escherichia coli O157:H7 were sprayed with 10% acetic acid (at 23 and 55 degrees C), 10% lactic acid (at 23 and 55 degrees C), 3% sodium hydroxide (at 23 degrees C) or 4 and 5% sodium metasilicate (at 23 degrees C). All antimicrobials were evaluated independently after being applied alone, being applied after a water rinse, or being followed by a water rinse. Antimicrobial treatments followed by a water rinse lowered E. coli O157:H7 populations by 0.6 to 2.4 log CFU/cm2 and resulted in hides with a surface pH of 6.3 to 9.2. Treatments in which a water rinse was followed by antimicrobial application lowered E. coli O157:H7 populations by 1.5 to 5.1 log CFU/cm2 but resulted in hides with a surface pH of 3.9 to 10.5. In study II, whole hides were treated with one of four antimicrobials (acetic acid, lactic acid, sodium hydroxide, or sodium metasilicate) followed by a water rinse. Hides were evaluated for aerobic bacterial counts, total coliform counts, and E. coli counts. Generally, all antimicrobials resulted in greater reductions (P < 0.05) of E. coli counts when compared with the control; however, only acetic and lactic acids resulted in greater reductions (P < 0.05) of aerobic bacterial counts and total coliform counts compared with the controls. These antimicrobials could be used to reduce microbial contamination on hides, potentially reducing microbiological contamination transferred to carcasses or to the plant environment.     

Seasonal prevalence of Shiga toxin-producing Escherichia coli, including O157:H7 and non-O157 serotypes, and Salmonella in commercial beef processing plants

The seasonal prevalence of Escherichia coli O157:H7, Salmonella, non-O157 E. coli (STEC), and stx-harboring cells was monitored at three Midwestern fed-beef processing plants. Overall, E. coli O157:H7 was recovered from 5.9% of fecal samples, 60.6% of hide samples, and 26.7% of carcasses sampled before the preevisceration wash. This pathogen also was recovered from 1.2% (15 of 1,232) of carcasses sampled at chilling (postintervention) at approximate levels of <3.0 cells per 100 cm2. In one case, the E. coli O157:H7 concentration dropped from ca. 1,100 cells per 320 cm2 at the preevisceration stage to a level that was undetectable on ca. 2,500 cm2 at the postintervention stage. The prevalence of E. coli O157:H7 in feces peaked in the summer, whereas its prevalence on hide was high from the spring through the fall. Overall, Salmonella was recovered from 4.4, 71.0, and 12.7% of fecal, hide, and preevisceration carcass samples, respectively. Salmonella was recovered from one postintervention carcass (of 1,016 sampled). Salmonella prevalence peaked in feces in the summer and was highest on hide and preevisceration carcasses in the summer and the fall. Non-O157 STEC prevalence also appeared to vary by season, but the efficiency in the recovery of isolates from stx-positive samples ranged from 37.5 to 83.8% and could have influenced these results. Cells harboring stx genes were detected by PCR in 34.3, 92.0, 96.6, and 16.2% of fecal, hide, preevisceration carcass, and postintervention carcass samples, respectively. The approximate level of non-O157 STEC and stx-harboring cells on postintervention carcasses was > or = 3.0 cells per 100 cm2 for only 8 of 199 carcasses (4.0%). Overall, the prevalence of E. coli O157:H7, Salmonella, and non-O157 STEC varied by season, was higher on hides than in feces, and decreased dramatically, along with pathogen levels, during processing and during the application of antimicrobial interventions. These results demonstrate the effectiveness of the current interventions used by the industry and highlight the significance of hides as a major source of pathogens on beef carcasses.     

Escherichia coli O157:H7 genetic diversity in bovine fecal samples

Escherichia coli O157:H7 causes foodborne illness in humans; cattle are considered a primary reservoir for the organism, and transmission is often through contaminated food products or water. The objective of this study was to determine the genetic diversity of E. coli O157:H7 within a single individual bovine fecal sample based on pulsed-field gel electrophoresis (PFGE) typing. Fecal samples (n=601) were collected from dairy and beef cattle at three separate facilities, and E. coli O157:H7 was isolated by enrichment, immunomagnetic separation, and plating on selective medium. The prevalence of E. coli O157:H7 was 46 (7.7%) of 601. From each positive fecal sample, up to 10 putative colonies were tested, and isolates from samples with at least seven positive colonies were subtyped using PFGE and tested for six major virulence genes by multiplex PCR. A total of 254 E. coli O157:H7 isolates from 27 samples met these criteria and were included in PFGE analysis. Fifteen PFGE subtypes (<100% Dice similarity) were detected among the 254 isolates, and there were no common subtypes between the three locations. Seven (26%) of 27 fecal samples had E. coli O157:H7 isolates with different PFGE subtypes (mean=2.1) within the same sample. The virulence gene profiles of different isolates from the same sample were always identical, regardless of the number of PFGE types. The results of this study suggest that determining the PFGE pattern of a single isolate from a bovine sample may not be sufficient when comparing isolates from feces, hides, or carcasses, because multiple PFGE subtypes are present.     

Escherichia coil O157 diversity with respect to survival during drying on concrete

Shiga toxin (Stx)-producing Escherichia coli O157 isolates (n = 123) were divided into groups according to origin, genotype (pulsed-field gel electrophoresis [PFGE] type, or ribotype), type of Stx produced, or phage type (PT). The survival rate ([number of CFU after 24 h of drying/number of CFU before drying] x 100) for each isolate was determined in triplicate after drying on concrete for 24.0 h. The overall mean survival rate among the 123 E. coli O157 isolates studied was 22.9%, but there was a wide range of responses to drying on concrete, with a minimum of 1.2% and a maximum of 61.9% of the initial inocula being recovered after drying. Among the groups, those isolates that originated from cases of human disease were, on average, significantly more sensitive (P < 0.001) to drying (with a mean survival rate of 15.3%) than isolates from the other three sources (with mean survival rates of 27.7, 26.0, and 22.9% for meats, bovine or ovine feces, and bovine hides, respectively). When the isolates were grouped by genotype, three of the PFGE types were, on average, significantly more resistant to drying than two other PFGE types were, and similarly, significant differences in average resistance to drying between groups of E. coil O157 with different ribotypes were seen. There were no differences between the abilities of isolates producing different Stxs (Stx 1 or Stx 1 and Stx 2) to survive drying. E. coli O157 isolates of PT4, PT21/28, and PT32 survived drying on concrete better than groups of other PTs did. Since the E. coli O157 isolates had various abilities to survive drying on concrete, drying could contribute to a kind of E. coil O157 natural selection along the meat chain. This possibility may have significant meat safety implications if a range of E. coil O157 isolates are simultaneously exposed to drying at any point along the meat production chain. Those E. coil O157 isolates that are more able to survive drying could be more likely to pass farther along the meat chain and ultimately reach consumers.