Pre-Harvest Control of E. Coli O157:H7 in Cattle

NON-TECHNICAL SUMMARY: Escherichia coli O157:H7 is an important and emerging cause of food borne illness in humans. Symptoms range from mild to bloody diarrhea, and hemolytic uremic syndrome, renal failure, and death are an occasional sequella.

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APPROACH: We do not expect the results of our proposed studies to provide definitive answers to this complex issue. However, the results of this work will provide useful insights into the species specificity of E. coli O157:H7 and help to direct future work. If we find genetic similarities between strains found in cattle, water, and wildlife in agricultural areas, it will have important repercussions in the design of on-farm pathogen control programs, changing our focus to multiple, rather than single, farms. If differences exist between human and bovine strains, it will direct our future work towards identifying means to differentiate strains based on potential pathogenicity to humans and towards understanding the mechanisms of pathogenicity. Both the experimental and field studies described under this objective will be completed in the spring of 2002. The results will be used to generate new hypotheses and seek additional funding for further studies in 2003 - 2005. We will identify management factors with the potential to be manipulated by producers that can be targeted to reduce fecal shedding of E. coli O157:H7 in live animals. Our proposed studies will provide preliminary evidence and allow us to prioritize potential control strategies for testing in intervention studies. The observation study will be completed by 2002, and intervention studies will be funded and performed between 2002 and 2006.

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PROGRESS: 2001/10 TO 2006/09<BR>
Escherichia coli O157 is a major cause of food borne illnesses in humans. Food products contaminated with cattle feces are a major source of E. coli O157 in outbreaks. Fecal shedding of E. coli O157 in cattle is reflective of the ability of the organism to persist or colonize the gastrointestinal tract. Twelve ruminally-cannulated cattle, adapted to forage or grain diet with or without monensin, were used to investigate the effects of diet and monensin on concentration and duration of ruminal persistence and fecal shedding of E. coli O157. Our study showed that forage-fed cattle were culture positive longer than grain-fed cattle. Monensin supplementation decreased the duration of shedding with forage diet, and the cecum and colon were culture positive for E. coli O157 more often the rumen in cattle. We conducted a study to compare the level and duration of fecal shedding of Escherichia coli O157:H7 between calves fed milk replacer with or without antibiotic (oxytetracycline and neomycin) supplementation. The probability and level of fecal shedding of E. coli O157 in the antibiotic-fed group was higher for most of the study period compared to the control group fed no antibiotic. We evaluated rectoanal mucosal swab (RAMS) sampling technique for prevalence of E. coli O157 in feedlot cattle. Samples collected by swabbing the rectoanal mucosa were shown to be superior to fecal samples for detecting prevalence of E. coli O157. Samples were collected from feed bunks in up to 10 feedlot pens within 54 commercial feedlots to determine the prevalence of E. coli O157 in feeds. Overall, E. coli O157 was detected in 76 of 504 feed bunk samples (15.1 percent) by one or both methods. We determined the prevalence of E. coli O157:H7 in house flies from a cattle feedlot: The prevalence of E. coli O157 was 2.9 and 1.4 percent in HF collected from feed bunks and cattle feed storage, respectively. Large populations of HF on cattle farms may play a role in the dissemination of E. coli O157 among animals and to the surrounding environment. A study, was conducted with diets were formulated to effect changes in hindgut fermentation to test our hypothesis that changes in hindgut ecosystem could have an impact on fecal shedding of E. coli O157. A subset of 40 heifers identified as being positive for fecal shedding of E. coli O157 were selected, housed in individual pens, and randomly allocated to four dietary treatments. Treatments were arranged as a 2 x 2 factorial, with factor 1 consisting of grain type (sorghum or wheat) and factor 2 being method of grain processing (steam-flaking or dry-rolling). Fecal and RAMS samples were obtained 3 times a week to isolate and identify E. coli O157. Average prevalence from d 9 was higher (P < 0.001) in cattle fed SF grains (65 percent) compared to those fed dry-rolled grains (30 percent). Average prevalence in cattle fed sorghum (50 percent) or wheat (30 percent) were similar (P > 0.10) on most sampling days. Results from this study indicated that feeding dry-rolled grains compared to steam-flaked grains reduced fecal shedding of E. coli O157.
<BR> <BR> IMPACT: 2001/10 TO 2006/09<BR>
Escherichia coli O157 is an emerging cause of food borne illnesses in humans. Food products contaminated with cattle feces are a major source of E. coli O157 in outbreaks. Reducing the level and duration of fecal shedding in cattle will reduce the potential contamination of carcasses. The long term goal of our research is to identify means to control E. coli O157 at the farm level. The goals of our research are to develop and validate improved methods for the detection of E. coli O157 in cattle feces and environmental samples, to improve our understanding of the natural ecology of E. coli O157 in cattle operations, and to identify and test on-farm intervention strategies for control of E. coli O157.

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PROGRESS: 2005/01/01 TO 2005/12/31<BR>
Escherichia coli O157 is a major cause of food borne illnesses in humans. Food products contaminated with cattle feces are a major source of E. coli O157 in outbreaks. Fecal shedding of E. coli O157 in cattle is reflective of the ability of the organism to persist or colonize the gastrointestinal tract. Evidence suggests that the site of persistence or colonization is in the hindgut and not the rumen. Hindgut (cecum, colon and rectum) is a major colonization site for E. coli O157 in cattle. In this study, diets were formulated to effect changes in hindgut fermentation to test our hypothesis that changes in hindgut ecosystem could have an impact on fecal shedding of E. coli 0157. Ninety-two crossbred yearling heifers (initial BW = 347 kg) were fed diets containing dry-rolled corn (DRC) or steam flaked corn (SFC) to assess the impact of grain processing on prevalence of E. coli O157. Steam flaking typically results in more extensive ruminal digestion, and thus less substrate flow to the hindgut, potentially altering populations of flora in the hindgut. During the prescreening phase, heifers (n=92) were fed a common DRC finishing diet. Heifers were screened for presence of E. coli O157 using a fecal grab sample (FECAL) and by swabbing the rectoanal mucosa (RAMS). Cattle that tested positive by either sampling technique (TOTAL; n=30) were randomly assigned to individual pens and fed diets consisting primarily of DRC or SFC. Cattle assigned to the SFC diet were transitioned from the DRC diet over a 9-d period. Cattle were again sampled using both techniques on days 14, 21, 28, 36, 43, and 50. Average daily gains during the study were 1.75 and 1.43 kg/day for cattle fed SFC and DRC, respectively (P<0.01). No differences in DMI were detected (P < 0.85) between SFC and DRC (8.44 and 8.52 kg/day, respectively), but gain efficiency was improved (P < 0.01) with SFC compared to DRC (0.207 and 0.168 kg/day, respectively). The prevalence of E. coli O157 for TOTAL remained above 50 percent for the first 14 days, and then declined over time (53, 33, 0, 27, 6, and 13 percent for DRC and 67, 27, 40, 40, 20, 6 percent for SFC on days 14, 21, 28, 36, 43 and 50, respectively). No treatment by day interactions were detected for TOTAL, RAMS, or FECAL (P > 0.70, P > 0.60, and P > 0.30, respectively). Feeding SFC improved performance of heifers compared to DRC, but did not impact E. coli O157 prevalence rates. This study demonstrated that it is feasible to utilize pre-screening as a method for identifying cattle that are positive for E. coli O157, and to subsequently use these animals to investigate the impact of preharvest intervention strategies on E. coli O157 prevalence rates.
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IMPACT: 2005/01/01 TO 2005/12/31<BR>
Understanding the ecology of E. coli O157 in cattle and cattle operations is critical to the development and implementation of on farm control programs aimed at minimizing the risk of transmission. Dietary ingredients, deed additives or probiotics are some of the approaches that could be used to reduce pathogen load in cattle.

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PROGRESS: 2004/01/01 TO 2004/12/31<BR>
We did a study was to compare the level and duration of fecal shedding of Escherichia coli O157:H7 between calves fed milk replacer with or without antibiotic (oxytetracycline and neomycin) supplemetation. Eighteen 1-week-old Holstein calves were orally inoculated with a strain of E. coli O157:H7 made resistant to naladixic acid (NA). Rectal samples were obtained from the calves following oral inoculation three times weekly up to 8 weeks. Fecal shedding of NA-resistant E. coli O157:H7 was quantified by direct plating or detected by selective enrichment procedure. Eight weeks post-inoculation, calves were euthanized, necropsied, and tissues (tonsils, retropharyngeal and mesenteric lymph nodes, and Peyers patches) and gut contents (rumen, omasum, abomasum, ileum, cecum, colon, and rectum) were sampled to quantify or detect NA-resistant E. coli O157:H7. The probability and level of fecal shedding of NA-resistant E. coli O157:H7 in the antibiotic-fed group was higher for most of the study period (until d 39) compared to the control group fed no antibiotic. A comparison of the duration of fecal shedding between the two groups showed no significant difference between the survival time probabilities of NA-resistant E. coli O157:H7. At necropsy, E. coli O157:H7 was recovered from the rumen and omasum of one calf in the control group and from retropharyngeal lymph node and Peyers patch of two calves in the antibiotic group. Supplementation of milk replacer with antibiotics may enhance the level and probability of E. coli O157:H7 shedding in pre-weaned dairy calves.
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IMPACT: 2004/01/01 TO 2004/12/31<BR>
Understanding the ecology of E. coli O157 in cattle and cattle operations is critical to the development and implementation of on farm control programs aimed at minimizing the risk of transmission. Dietary ingredients, deed additives or probiotics are some of the apparoaches that could be used to reduce pathogen load in cattle.

<BR> <BR> PROGRESS: 2003/01/01 TO 2003/12/31<BR>
Our objectives were to study the influence of dietary ingredients and feed additives on growth and fecal shedding of E. coli O157:H7 in cattle. Ionophores are used extensively in many segments of cattle industry. Monensin is the most commonly fed ionophore to cattle. A pure culture study was conducted to investigate whether monensin influences the growth of both nalidixic acid (NalR) and non-nalidixic acid resistant E. coli O157:H7. Six strains (NalR Frik 920, NalR Frik 2000, NalR Frik 1123. Frik 1123, 01-4-1848 Omaha, and ATCC 43890) of E. coli O157:H7. All six strains of E. coli O157:H7 inoculated into GN broth with or without monensin grew with similar growth rates. It does not appear that monensin included into GN broth at a concentration 20 times the expected level found in the rumen of cattle fed at recommended dose influenced the growth of E. coli O157:H7. Two studies to determine the effect of probiotics or Direct-Fed Microbials (DFM) on fecal shedding of E. coli O157 in cattle were conducted. In one study, sixteen beef steer calves were randomly allotted to one of four treatment groups: control (no DFM), and DFM dosed daily at 2, 20, or 200 g per head. The DFM consisted of two strains of Enterococcus faecium in a 50: 50 blend to deliver a 5 x 109 CFU/hd/day in a 2 g dose. Calves were adapted to corn grain based diet with monensin and DFM was dosed orally beginning 9 days before challenge with E. coli O157. Calves were orally inoculated with a mix of two strains of nalidixic acid-resistant (Nalr) E. coli O157:H7 (5.2 x 1010 cfu/animal). Fecal samples were collected three times a wk for 4 wk and the presence and concentration of Nalr E. coli O157:H7 were determined. Groups fed DFM at 2 or 20 g shed lower concentrations of Nalr E. coli O157:H7 in the feces compared to the control (P = 0.06 and 0.01, respectively). DFM at 200 g had no effect on fecal shedding of Nalr E. coli O157:H7. In the second study, 240 steers were randomly allocated to 30 pens with 8 animals in each pen. Pens were randomly assigned to two treatment groups: control (no DFM) or 20 g daily dose of E. faecium-based DFM. Two weeks after initiating DFM dosing, fecal samples were collected for isolation to assess prevalence of E. coli O157:H7. The control group had 8/15 pens compared to 3/15 pens in the DFM-fed group with at least one animal positive for E. coli O157:H7. Chi square analysis of the probability of at least one animal within a pen testing positive for the control and DFM-fed indicated a trend (P = 0.058) for DFM reducing prevalence of E. coli O157:H7. Results suggest potential benefit of feeding DFM in reducing prevalence of E. coli O157:H7 in grain-fed cattle.
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IMPACT: 2003/01/01 TO 2003/12/31<BR>
Understanding the influence of diet ingredients and feed additives on fecal shedding of E. coli O157:H7 could provide critical control point in on-farm pathogen reduction programs. Direct-fed microbial feed additives may be a preharvest management tool to control or eliminate the pathogen.

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PROGRESS: 2002/01/01 TO 2002/12/31<BR>
Data analysis was completed on a field study to determine the associations between management factors and fecal shedding with E-coli O157 in feedlot cattle. A total of 14,424 samples were collected from cattle feces, water, and feed in 711 pens on 73 feedlots in 4 major cattle-feeding states. The samples were tested for E-coli O157 using standard enrichment and detection procedures. Data on feedlot management practices were collected by survey. The overall prevalence of E-coli O157 was 9.1 percent. Factors related to water quality, the presence of vermin, and weather were associated with E-coli O157. Currently, we are performing PFGE to genetically characterize the isolates. Gut contents from 424 cattle at slaughter were tested for E-coli O157. The prevalence was 12.7, 7.8, 9.0, and 6.4 percent in rectum, colon, cecum, and rumen, respectively. The isolates of E. coli O157 obtained in this study are being genetically characterized using PFGE to determine whether the same strains exist at different sites within the same animal. Using an oral challenge model with E-coli O157, cattle on a high forage diet shed higher numbers of bacteria, and for longer, compared to cattle fed a high grain diet. Monensin supplementation decreased shedding of E-coli O157 in the steers on the high forage diet. A second challenge study compared the level and duration of fecal shedding of E. coli O157 between calves fed commercial milk replacer with or without antibiotic supplementation (200 mg/kg oxytetracycline and 400 mg/kg neomycin). The concentration of E-coli O157 shed in the antibiotic treated group was higher for most of the study period compared to the non-antibiotic treated group. However, antibiotic supplementation had not significant effect on the duration of fecal shedding of E-coli O157.
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IMPACT: 2002/01/01 TO 2002/12/31<BR>
Understanding the ecology of E-coli O157 is critical to the implementation of on-farm control programs aimed at minimizing the risk of E-coli O157 in human food. Identifying management associations with E-coli O157 will provide producers with a practical means of reducing this pathogen at the farm level. Thus, the results from this project study will have important implications on the practical application of E-coli O157 control at the farm level.

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PROGRESS: 2001/01/01 TO 2001/12/31<BR>
The objectives of this project are 1) to determine the degree of species specificity of E-coli O157, and 2) to identify critical control points for on-farm control. Under objective 1, we have completed a challenge trial in calves that compared fecal shedding of E-coli O157 in calves inoculated with strains of E-coli O157 of bovine versus human origin. Calves inoculated with strains of bovine origin shed the pathogen at higher levels, were more likely to resume shedding following weaning, and were more likely to have the pathogen present in the GI tract at necropsy (8 weeks post-challenge). There were no significant differences in the duration of fecal shedding between groups. In an epidemiological study of E-coli O157 in pasture environments, identical genetic strains of E-coli O157 were found in cattle, water, and a feral oppossum. A field study was conducted to determine the associations between management factors and fecal shedding with E-coli O157 in feedlot cattle. A total of 14,424 samples were collected from cattle feces, water, and feed in 711 pens on 73 feedlots in 4 major cattle-feeding states. The samples were tested for E-coli O157 using bacteriological culture. Data on feedlot management practices were collected by survey. The overall prevalence was of E-coli O157 was 9.1%. Statistical analysis to identify significant associations with management factors is ongoing.
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IMPACT: 2001/01/01 TO 2001/12/31<BR>
Understanding the ecology of E-coli O157 and the role of both cattle and non-cattle sources is critical to the implementation of on-farm control programs aimed at minimizing the risk of E-coli O157 in human food. Identifying management associations with E-coli O157 will provide producers with a practical means of reducing this pathogen at the farm level. Thus, the results from this project study will have important implications on the practical application of E-coli O157 control at the farm/pasture level in the beef industry.