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.     

Treatments using hot water instead of lactic acid reduce levels of aerobic bacteria and Enterobacteriaceae and reduce the prevalence of Escherichia coil O157:H7 on preevisceration beef carcasses

Lactic acid has become the most commonly used organic acid for treatment of postevisceration beef carcasses. Many processors have also implemented 2% lactic acid washes on preevisceration carcasses. We previously demonstrated that hot water washing and steam vacuuming are effective carcass interventions. Because of the effectiveness of hot water, we compared its use with that of lactic acid as a preevisceration wash in a commercial setting. A commercial hot water carcass wash cabinet applying 74 degrees C (165 degrees F) water for 5.5 s reduced both aerobic plate counts and Enterobacteriaceae counts by 2.7 log CFU/100 cm2 on preevisceration carcasses. A commercial lactic acid spray cabinet that applied 2% L-lactic acid at approximately 42 degrees C (105 to 110 degrees F) to preevisceration carcasses reduced aerobic plate counts by 1.6 log CFU/100 cm2 and Enterobacteriaceae counts by 1.0 log CFU/100 cm2. When the two cabinets were in use sequentially, i.e., hot water followed by lactic acid, aerobic plate counts were reduced by 2.2 log CFU/100 cm2 and Enterobacteriaceae counts were reduced by 2.5 log CFU/100 cm2. Hot water treatments reduced Escherichia coli O157:H7 prevalence by 81%, and lactic acid treatments reduced E. coli O157:H7 prevalence by 35%, but the two treatments in combination produced a 79% reduction in E. coli O157:H7, a result that was no better than that achieved with hot water alone. These results suggest that hot water would be more beneficial than lactic acid for decontamination of preevisceration beef carcasses.     

Seasonal prevalence of Escherichia coli O157:H7 in beef cattle feces

Cattle are an asymptomatic reservoir of Escherichia coli O157:H7, but the bacterial colonization and shedding patterns are poorly understood. The prevalence and shedding of this human pathogen have been reported to be seasonal with rates typically increasing during warm months. The objectives of this study were (i) to assess the prevalence of E. coli O157:H7 in feces of feedlot cattle in Kansas during summer, fall, and winter months, and (ii) to characterize E. coli O157:H7 by screening for virulence factors. Of 891 fecal samples collected, 82 (9.2%) were positive for E. coli O157:H7. No significant differences in prevalence were detected among summer, fall, and winter months. The highest monthly prevalence (18.1%) was detected in February. All tested isolates were positive for stx2 (Shiga toxin 2) and eaeA (intimin) genes; 14 isolates (12.8%) also carried stx1. Our results indicate the prevalence of E. coli O157:H7 in beef cattle feces is not necessarily season dependent.     

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.     

Isolation and characterization of Shiga toxin-producing Escherichia coli O157:H7 and non-O157 from beef carcasses at a slaughter plant in Mexico

The contamination of beef carcasses with Shiga toxin-producing O157:H7 and non-O157 Escherichia coli (STEC) obtained from a slaughter plant in Guadalajara, Mexico was investigated. A total of 258 beef carcasses were sampled during a 12-month period. All samples were assayed for STEC by selective enrichment in modified tryptone soy broth supplemented with cefixime, cefsulodin and vancomycin, followed by plating on Sorbitol MacConkey Agar supplemented with cefixime and tellurite (CT-SMAC). Simultaneously, all samples were assayed by immunomagnetic separation (IMS) and plated on CT-SMAC and CHROMagar. The presence of the stx1, stx2, eaeA and hly933 genes, recognized as major virulence factors of STEC, was tested for O157:H7 and non-O157 E. coli isolates by multiplex polymerase chain reaction (PCR). STEC was detected in two (0.8%) samples. One of these STEC isolates corresponded to the serotype O157:H7 showing stx2, eaeA and hyl933 genes. The other isolate corresponded to non-O157 STEC and only had the stx1 gene. Thirteen carcasses (5%) were positive for nonmotile E. coli O157 and 7 (2.7%) were positive for E. coli O157:H7. The presence of O157:H7 and non-O157 STEC on beef carcasses in this slaughter plant in Guadalajara, Mexico, emphasizes the importance of implementing the Hazard Analysis and Critical Control Point (HACCP) system, as well as the need for implementing, evaluating, and validating antimicrobial interventions to reduce the presence of potential pathogenic microorganisms.     

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.     

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.     

Effect of different levels of beef bacterial microflora on the growth and survival of Escherichia coli O157:H7 on beef carcass tissue

The influence of various levels of endogenous beef bacterial microflora on the growth and survival of Escherichia coli O157:H7 on bovine carcass surface tissue was investigated. Bacterial beef microflora inoculum was prepared by enriching and harvesting bacteria from prerigor lean bovine carcass tissue (BCT) and was inoculated onto UV-irradiated prerigor BCT at initial levels of 10(5), 10(4), 10(3), and <10(3) CFU/cm2. Additional control BCT was inoculated with sterile H2O. E. coli O157:H7 was inoculated onto all tissues at an initial level of 10(2) CFU/cm2. Following a 48-h incubation at 4 degrees C, BCT was incubated up to 14 days at 4 or 12 degrees C, either aerobically or vacuum packaged. Regardless of the microflora level, there was no substantial growth of E. coli O157:H7 on BCT during storage at 4 degrees C under either aerobic or vacuum-packaged conditions. Instead, viable cell numbers at 4 degrees C remained constant, with no reduction in numbers associated with the different beef microflora levels. E. coli O157:H7 grew on all BCT stored at 12 degrees C, regardless of microflora inoculation treatment, reaching higher populations on aerobic samples than on vacuum-packaged samples in 10 days. However, the presence of the beef microflora did appear to delay the onset of growth or slow the growth of the pathogen, and E. coli O157:H7 counts on BCT without added microflora were generally higher following 7 to 10 days of 12 degrees C storage than those counts on BCT inoculated with beef microflora. These data demonstrate the importance of temperature control during meat handling and storage to prevent the outgrowth of this pathogen and indicate that proper sanitation and processing practices that prevent and reduce contamination of carcasses with E. coli O157:H7 are essential, regardless of background microflora levels.     

Escherichia coli O157:H7 prevalence in fecal samples of cattle from a southeastern beef cow-calf herd

The proportion of fecal samples culture-positive for Escherichia coli O157:H7 was determined for samples collected from 296 beef cows on pasture in a single Florida herd in October, November, and December 2001. The overall proportion of samples that cultured positive was 0.03. The proportion of cows that were culture-positive on at least one occasion was 0.091. No effect of pregnancy status or nutritional regimen on the proportion of culture-positive samples for E. coli O157:H7 was detected. We detected a breed effect on the shedding of E. coli O157, with Romosinuano cows having a lower (P < 0.01) proportion of samples culture-positive than Angus or Brahman cows. This difference might have resulted from the presence of confounding variables; however, it also might represent evidence of breed-to-breed genetic variation in E. coli O157 shedding. Further research is warranted to evaluate breed as a possible risk factor for shedding of this important foodborne pathogen. Further substantiated findings could indicate that breed is a cow-calf-level critical control point of E. coli O157:H7.     

Lethality of commercial whole-muscle beef jerky manufacturing processes against Salmonella serovars and Escherichia coli O157:H7

Thermal processes used in making whole-muscle beef jerky include a drying step, which may result in enhanced pathogen thermotolerance and evaporative cooling that reduce process lethality. Several salmonellosis outbreaks have been associated with beef jerky. In this study, a standardized process was used to inoculate beef strips with five-strain cocktails of either Salmonella serovars or Escherichia coli O157:H7, to marinate the strips at pH 5.3 for 22 to 24 h at 5 degrees C, and to convert the strips to jerky using various heating and drying regimes. Numbers of surviving organisms were determined during and after heating and drying. Salmonella reductions of > or = 6.4 log CFU and similar reductions in E. coli O157:H7 were best achieved by ensuring that high wet-bulb temperatures were reached and maintained early in the process (51.7 or 54.4 degrees C for 60 min, 57.2 degrees C for 30 min, or 60 degrees C for 10 min) followed by drying at 76.7 degrees C (dry-bulb temperature). Processes with less lethality that reduced counts of both pathogens by > or = 5.0 log CFU were (i) heating and drying at 76.7 degrees C (dry bulb) within 90 min of beginning the process, (ii) heating for successive hourly intervals at 48.9, 54.4, 60, and 76.7 degrees C (dry bulb), and (iii) heating at 51.7 degrees C (dry bulb) and then drying at 76.7 degrees C (dry bulb), starting before the product water activity dropped below 0.86. In several trials, separate beef strips were inoculated with a commercial Pediococcus acidilactici starter culture as a potential surrogate for evaluating pathogen thermotolerance. The results of these trials suggested that this experimental approach may be useful for in-plant validation of process lethality.     

Prevalence and level of Escherichia coli O157 on beef trimmings, carcasses and boned head meat at a beef slaughter plant

This study investigated the prevalence and level of Escherichia coli O157 on samples of beef trimmings (n=1351), beef carcasses (n=132) and bovine head meat (n=132) in a beef slaughter plant in Ireland. The survey also included an assessment of the prevalence of virulence genes in the E. coli O157 isolates obtained. Samples were examined for the presence of E. coli O157 by direct plating on SMAC-CT and by enrichment/immunomagnetic separation (IMS) with plating of recovered immunobeads onto SMAC-CT agar. Presumptive E. coli O157 isolates were confirmed by PCR targeting a range of genes i.e. vt1, vt2, eaeA, hlyA, fliC(h7) and portions of the rfb (O-antigen encoding) region of E. coli O157. Enterobacteriaceae on head meat samples were estimated by direct plating onto Violet Red Bile Glucose agar. E. coli O157 was recovered from 2.4% (32/1351) of beef trimmings samples, at concentrations ranging from<0.70-1.61 log10 cfu g(-1). Of the 32 positive isolates, 31 contained the eaeA and hylA genes while 30/32 contained the fliC(h7) gene and 31/32 contained vt1 or vt2, or both vt genes. E. coli O157 was recovered from 3.0% (4/132) of carcass samples, at concentrations ranging from <0.70-1.41 log10 cfu g(-1). All of the carcass isolates contained the eaeA, hylA and fliC(h7) genes. E. coli O157 was recovered from 3.0% (3/100) of head meat samples, at concentrations of 0.7-1.0 log10 cfu g(-1). All of the head meat isolates contained the eaeA, hylA, fliC(h7) and vt2 genes. No head meat isolates contained the vt1 gene. Head meat samples (n=100) contained Enterobacteriaceae, at concentrations ranging from 0.70-3.0 log10 cfu g(-1). Overall, the qualitative and quantitative data obtained for E. coli O157 on beef trimming samples in this study could be employed as part of a quantitative risk assessment model.     

Escherichia coli O157:H7 shedding in vaccinated beef calves born to cows vaccinated prepartum with Escherichia coli O157:H7 SRP vaccine

Extensive research, intervention equipment, money, and media coverage have been directed at controlling Escherichia coli O157:H7 in beef cattle. However, much of the focus has been on controlling this pathogen postcolonization. This study was conducted to examine the performance, health, and shedding characteristics of beef calves that were vaccinated with an E. coli O157:H7 SRP bacterial extract. These calves had been born to cows vaccinated prepartum with the same vaccine. Cows and calves were assigned randomly to one of four treatments: (i) neither cows nor calves vaccinated with E. coli O157:H7 SRP (CON), (ii) cows vaccinated with E. coli O157:H7 SRP prepartum but calves not vaccinated (COWVAC), (iii) calves vaccinated with E. coli O157:H7 SRP but born to cows not vaccinated (CALFVAC), (iv) cows vaccinated with E. coli O157:H7 SRP prepartum and calves also vaccinated (BOTH). Calves born to vaccinated cows had significantly higher titers of anti-E. coli O157:H7 SRP antibodies (SRPAb) in circulation at branding time (P < 0.001). Upon entry to the feedlot, overall fecal E. coli O157:H7 prevalence was 23 % among calves, with 25 % in the CON treatment group, 19 % in the CALFVAC group, 32 % in the COWVAC group, and 15 % in the BOTH group (P > 0.05). Fecal shedding of E. coli O157 on arrival to the feedlot was not correlated with fecal shedding at slaughter (Spearman's rho = -0.02; P = 0.91). No significant effects of cow or calf E. coli O157:H7 SRP vaccination treatment were found on feedlot calf health or performance (P > 0.05), prevalence of lung lesions or liver abscess (P > 0.05), or morbidity, retreatment, or mortality numbers (P > 0.05). The findings of this study indicate that the timing of vaccination of calves against E. coli O157:H7 may be an important consideration for maximizing the field efficacy of this vaccine.     

Fate of Shiga toxin-producing O157:H7 and non-O157:H7 Escherichia coli cells within blade-tenderized beef steaks after cooking on a commercial open-flame gas grill

We compared the fate of cells of both Shiga toxin-producing Escherichia coli O157:H7 (ECOH) and Shiga toxin-producing non-O157:H7 E. coli (STEC) in blade-tenderized steaks after tenderization and cooking on a gas grill. In phase I, beef subprimal cuts were inoculated on the lean side with about 5.5 log CFU/g of a five-strain mixture of ECOH or STEC and then passed once through a mechanical blade tenderizer with the lean side facing up. In each of two trials, 10 core samples were removed from each of two tenderized subprimals and cut into six consecutive segments starting from the inoculated side. Ten total cores also were obtained from two nontenderized (control) subprimals, but only segment 1 (the topmost segment) was sampled. The levels of ECOH and STEC recovered from segment 1 were about 6.0 and 5.3 log CFU/g, respectively, for the control subprimals and about 5.7 and 5.0 log CFU/g, respectively, for the tenderized subprimals. However, both ECOH and STEC behaved similarly in terms of translocation, and cells of both pathogen cocktails were recovered from all six segments of the cores obtained from tenderized subprimals, albeit at lower levels in segments 2 to 6 than those found in segment 1. In phase II, steaks (2.54 and 3.81 cm thick) cut from tenderized subprimals were subsequently cooked (three steaks per treatment) on a commercial open-flame gas grill to internal temperatures of 48.9, 54.4, 60.0, 65.6, and 71.1°C. Regardless of temperature or thickness, we observed 2.0- to 4.1-log and 1.5- to 4.5-log reductions in ECOH and STEC levels, respectively. Both ECOH and STEC behaved similarly in response to heat, in that cooking eliminated significant numbers of both pathogen types; however, some survivors were recovered due, presumably, to uneven heating of the blade-tenderized steaks.     

Effect of chemical sanitizer combined with modified atmosphere packaging on inhibiting Escherichia coli O157:H7 in commercial spinach

Escherichia coli O157:H7 contaminated spinach has recently caused several outbreaks of human illness in the USA and Canada. However, to date, there has been no study demonstrating an effective way to eliminate E. coli O157:H7 in spinach. Therefore, this study was conducted to investigate the effect of chemical sanitizers alone or in combination with packaging methods such as vacuum and modified atmosphere packaging (MAP) on inactivating E. coli O157:H7 in spinach during storage time. Spinach inoculated with E. coli O157:H7 was packaged in four different methods (air, vacuum, N(2) gas, and CO(2) gas packaging) following treatment with water, 100 ppm chlorine dioxide, or 100 ppm sodium hypochlorite for 5 min at room temperature and stored at 7+/-2 degrees C. Treatment with water did not significantly reduce levels of E. coli O157:H7 in spinach. However, treatment with chlorine dioxide and sodium hypochlorite significantly decreased levels of E. coli O157:H7 by 2.6 and 1.1 log(10)CFU/g, respectively. Levels of E. coli O157:H7 in samples packaged in air following treatments grew during storage time, whereas levels were maintained in samples packaged in other packaging methods (vacuum, N(2) gas, and CO(2) gas packaging). Therefore there were significant differences (about 3-4 log) of E. coli O157:H7 populations between samples packed in air and other packaging methods following treatment with chemical sanitizers after 7 days storage. These results suggest that the combination of treatment with chlorine dioxide and packaging methods such as vacuum and MAP may be useful for improving the microbial safety of spinach against E. coli O157:H7 during storage.     

Presence of Escherichia coli O157:H7 in ground beef and ground baby beef meat

A total of 114 beef and baby beef samples were examined. The samples included ground baby beef, mixed ground baby beef and pork, and chopped and shaped meat. The samples were analyzed from 30 different grocery stores in Zagreb, Croatia. The object of this study was to evaluate the prevalence of Escherichia coli O157:H7 in the samples that can enhance the potential risk of outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. The results in all tested samples of E. coli O157:H7 were negative. A single sample was positive in a latex agglutination test using antiserum to O157:H7. It was identified as Proteus vulgaris at the Pasteur Institute, Paris, France. This result correlates positively with cross-contamination with Yersinia enterocolitica 09, Brucella abortus, Salmonella type N, and Pseudomonas maltophila.     

High levels of background flora inhibits growth of Escherichia coli O157:H7 in ground beef

The influence of natural background flora under aerobic and anaerobic incubation on the growth of Escherichia coli O157:H7 in ground beef was investigated. The background flora from eight different commercial ground beef were added to ground beef spiked with E. coli O157:H7 and stored either aerobically or anaerobically at 12 degrees C. The results showed that the presence of a large number of background bacteria in the ground meat inhibited the growth of E. coli O157:H7 both aerobically and anaerobically. Inhibition was more pronounced under anaerobic conditions. The background floras consisted mainly of lactic acid bacteria of which approximately 80% were Lactobacillus sakei. These results show the importance of the natural background flora in meat for inhibition of growth of 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.     

An evaluation of rapid methods for detecting Escherichia coli O157 on beef carcasses

Numbers of Escherichia coli O157 in food may be low and sensitive techniques are therefore needed for its detection. The objectives of this study were to use carcass meat samples artificially inoculated with various strains of E. coli O157 to compare the sensitivity of enrichment in three different media and to compare immunomagnetic separation followed by culture of magnetic beads to cefixime tellurite sorbitol MacConkey agar with three immunoassays for the detection of E. coli O157 in the enrichment cultures. Duplicate 250, 25 and 2-3 CFU of each of 16 strains of E. coli O157 added to 25-g samples of beef carcass meat were used to compare the sensitivity of (1) enrichment in supplemented tryptone soya broth (sTSB), Reveal 8-h and Reveal 20-h media, and (2) immunomagnetic separation and culture to cefixime tellurite sorbitol MacConkey agar (IMS/CT-SMAC) with Reveal, VIP and STAT immunoassays for detecting the organism. An initial inoculum of 250 CFU/25 g meat was detected in all 32 samples by IMS/CT-SMAC performed on all enrichment media and by Reveal performed on Reveal 8-h and Reveal 20-h media, but in only 30, 19 and 9 samples by Reveal, VIP and STAT, respectively, performed on sTSB medium. An initial inoculum of 25 CFU/25 g meat was detected in 28, 32 and 30 of 32 samples by IMS/CT-SMAC performed on sTSB, Reveal 8-h and Reveal 20-h media, respectively, and in 32 and 30 samples by Reveal performed on Reveal 8-h and Reveal 20-h media, but in only 22, 11 and 2 samples by Reveal, VIP and STAT, respectively, performed on sTSB medium. An initial inoculum of 2-3 CFU/25 g meat was detected in 25, 31 and 28 of 32 samples by IMS/CT-SMAC performed on sTSB, Reveal 8-h and Reveal 20-h media, respectively, and in 25 and 23 samples by Reveal performed on Reveal 8-h and Reveal 20-h media, but in only 14, 1 and 0 samples by Reveal, VIP and STAT, respectively, performed on sTSB medium.     

Process control and sampling for Escherichia coli O157:H7 in beef trimmings

Raw beef producers currently face the problem of Escherichia coli O157:H7 surface contamination of beef carcasses that can lead to product adulteration. Although carcass interventions are in place, elimination of E. coli O157:H7 from every potential hiding place on the surfaces of a beef carcass is not technologically feasible. Therefore, E. coli O157:H7 on beef carcasses might further contaminate the surfaces of beef trimmings. With the use of case scenarios from nine commercial processing facilities, we present a process control and statistical sampling approach for monitoring beef trimmings to divert contaminated lots of the trimmings from the raw ground beef supply chain.     

Occurrence of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella and Campylobacter spp. on beef carcasses in Northern Ireland

A survey of beef carcasses was conducted in all 10 European community approved abattoirs in Northern Ireland to determine the incidence of Escherichia coli O157:H7. Analyses were based on excised samples of neck meat taken less than 48 h post-kill. Overall, 780 carcasses were sampled and all were negative for E. coli O157:H7. A sub-set of samples was analysed for the presence of Listeria monocytogenes (n=200), Salmonella (n=200) and Campylobacter spp.(n=100). L. monocytogenes was not detected but Listeria innocua was found on five carcasses and Listeria seeligeri on one. Three carcasses carried salmonellas; Salmonella Mbandaka was found on two and Salmonella Thompson on one. Campylobacter spp. were not detected on any carcasses. The results indicate that very few beef carcasses in Northern Ireland appear to carry any of the four pathogens sought, and this may help explain the low incidence of E. coli O157:H7 in the Northern Ireland human population, relative to the rest of the UK.