Escherichia coli O157:H7 excretion by commercial feedlot cattle fed either barley- or corn-based finishing diets

Effective preharvest control measures for Escherichia coli O157:H7 in cattle may significantly reduce the incidence of human disease caused by this organism. The prevalence and magnitude of fecal E. coli O157:H7 excretion was evaluated in 15 pens (300 to 500 cattle per pen) of commercial feedlot cattle fed a barley-based finishing ration and compared with that in 15 pens of cattle fed a corn-based ration. Average E. coli O157:H7 prevalence was 2.4% in barley-fed cattle and 1.3% in the corn-fed cattle (P < 0.05), and average magnitude of fecal E. coli O157:H7 excretion was 3.3 log CFU/g in the barley-fed cattle and 3.0 log CFU/g in the corn-fed cattle (P < 0.01). Corn-fed cattle had lower average fecal pH values (5.85) than did barley-fed cattle (6.51) (P < 0.01), and the average total generic fecal E. coli concentration in this group of animals (6.24 log CFU/g) was greater than that in the barley-fed cattle (5.55 log CFU/g) (P < 0.01). Specific feed ingredients may impact the frequency and magnitude of fecal excretion of E. coli O157:H7 by cattle.     

Effects of diet on rumen proliferation and fecal shedding of Escherichia coil O157:H7 in calves

Calves inoculated with Escherichia coli O157:H7 and fed either a high-roughage or high-concentrate diet were evaluated for rumen proliferation and fecal shedding of E. coli O157:H7. Calves fed the high-roughage diet had lower mean rumen volatile fatty acid concentrations and higher rumen pH values than did calves fed the high-concentrate diet. Despite these differences in rumen conditions, the calves fed the high-roughage diet did not have greater rumen populations of E. coli O157: H7 and did not exhibit increased or longer fecal shedding compared with the calves fed the high-concentrate diet. Two calves shedding the highest mean concentrations of E. coli O157:H7 were both fed the high-concentrate diet. There was a significant (P < 0.05) positive correlation between fecal shedding and rumen volatile fatty acid concentration in calves fed a high-concentrate diet. The effects of diet on E. coli O157:H7 proliferation and acid resistance were investigated using an in vitro rumen fermentation system. Rumen fluid collected from steers fed a high-roughage diet, but not from steers fed a high-concentrate diet, supported the proliferation of E. coli O157:H7. Rumen fluid from steers fed a high-concentrate diet rapidly induced acid resistance in E. coli O157:H7. The impact of diet on fecal shedding of E. coli O157:H7 is still unclear and may depend on dietary effects on fermentation in the colon and on diet-induced changes in the resident microflora. However, rapid development of acid tolerance by E. coli O157:H7 in the rumens of calves fed high-concentrate diets, allowing larger populations to survive passage through the acidic abomasum to proliferate in the colon, may be one factor that influences fecal shedding in cattle on feed.     

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.     

Influence of transportation stress and animal temperament on fecal shedding of Escherichia coli O157:H7 in feedlot cattle

To test the influence of transportation stress and temperament on shedding of Escherichia coli O157:H7, cattle (n=150) were classified at various stages of production as Excitable, Intermediate or Calm based on a variety of disposition scores. Presence of E. coli O157:H7 was determined by rectal swabs from live animals and from colons collected postmortem. Percentage of cattle shedding E. coli O157:H7 at arrival at the feedlot was approximately equal among temperament groups. Before shipment to the processing facility, a higher (P=0.03) proportion of cattle from the Calm group shed E. coli O157:H7 compared to the other temperament groups. When pooled across all sampling periods, cattle from the Calm group had a greater percentage test positive for E. coli O157:H7. Neither the acute stressor of transportation nor a more excitable temperament led to increased shedding of E. coli O157:H7 in cattle.     

Escherichia coli O157:H7 populations in ruminants can be reduced by orange peel product feeding

Foodborne pathogenic bacteria such as Escherichia coli O157:H7 are threats to the safety of beef. Citrus peel and dried orange pulp are by-products from citrus juice production that have natural antimicrobial effects and are often incorporated into least-cost ration formulations for beef and dairy cattle. This study was designed to determine if orange peel and pulp affected E. coli O157:H7 populations in vivo. Sheep (n = 24) were fed a cracked corn grain-based diet that was supplemented with a 50-50 mixture of dried orange pellet and fresh orange peel to achieve a final concentration (dry matter basis, wt/wt) of 0, 5, or 10% pelleted orange peel (OP) for 10 days. Sheep were artificially inoculated with 10(10) CFU of E. coli O157:H7 by oral dosing. Fecal shedding of E. coli O157:H7 was measured daily for 5 days after inoculation, after which all animals were humanely euthanized. At 96 h postinoculation, E. coli O157:H7 shedding was reduced (P < 0.05) in sheep fed 10% OP. Populations of inoculated E. coli O157:H7 were reduced by OP treatment throughout the gastrointestinal tract; however, this reduction reached significant levels in the rumen (P < 0.05) of sheep fed 10% OP diets. Cecal and rectal populations of E. coli O157:H7 were reduced (P < 0.05) by inclusion of both 5 and 10% OP diets. Our results demonstrate that orange peel products can be used as a preharvest intervention strategy as part of an integrated pathogen reduction scheme.     

Prevalence and molecular characterization of Escherichia coli O157:H7 by multiple-locus variable-number tandem repeat analysis and pulsed-field gel electrophoresis in three sheep farming operations in California

A year-long study was conducted to determine the fecal prevalence of Escherichia coli O157:H7 in three sheep ranches. Strain diversity and persistence were compared with multiple-locus variable-number tandem repeat analysis and pulsed-field gel electrophoresis. Ranch C, a feedlot, consisted of young sheep raised predominantly on a high-grain diet. The other two sites consisted of sheep raised on native pasture and a combination of native and irrigated pasture. Forty fecal samples were collected every month from each ranch. Samples were examined for E. coli O157:H7 by immunomagnetic separation and culture of the magnetic beads onto selective media. Detection of virulence markers in positive isolates was determined by PCR. E. coli O157:H7 was isolated from 100 (22.7%) of 440 fecal samples collected from ranch C. On ranch B, 9 (1.9%) of the 480 fecal samples were positive for the pathogen, while none of the samples from ranch A were positive. On ranch C, the odds of detecting E. coli O157:H7 was 3.2 times greater during the warmer months compared with the cooler months of the year. There was no association between days spent in the feedlot and fecal prevalence of the pathogen (P = 0.62). Most multiple-locus variable-number tandem repeat analysis types were isolated only once from ranch C (14 of 23), but several strains were isolated over 4 to 6 months, often in many intervening negative months. This study revealed that the prevalence of E. coli O157:H7 can be high in some sheep ranches in California, especially in feedlots where young sheep are fed predominantly high-grain rations.     

Molecular characterization of Escherichia coli O157:H7 hide contamination routes: feedlot to harvest

This study was conducted to identify the origin of Escherichia coli O157:H7 contamination on steer hides at the time of harvest. Samples were collected from the feedlot, transport trailers, and packing plant holding pens and from the colons and hides of feedlot steers. A total of 50 hide samples were positive for E. coli O157:H7 in two geographical locations: the Midwest (25 positive hides) and Southwest (25 positive hides). Hide samples were screened, and the presence of E. coli O157: H7 was confirmed. E. coli O157:H7 isolates were fingerprinted by pulsed-field gel electrophoresis and subjected to multiplex PCR procedures for amplification of E. coli O157:H7 genes stx1, stx2, eaeA, fliC, rfbEO157, and hlyA. Feedlot water trough, pen floor, feed bunk, loading chute, truck trailer side wall and floor, packing plant holding pen floor and side rail, and packing plant cattle drinking water samples were positive for E. coli O157:H7. Pulsed-field gel electrophoresis banding patterns were analyzed after classifying isolates according to the marker genes present and according to packing plant. In this study, hide samples positive for E. coli O157:H7 were traced to other E. coli O157:H7-positive hide, colon, feedlot pen floor fecal, packing plant holding pen drinking water, and transport trailer side wall samples. Links were found between packing plant side rails, feedlot loading chutes, and feedlot pens and between truck trailer, different feedlots, and colons of multiple cattle. This study is the first in which genotypic matches have been made between E. coli O157:H7 isolates obtained from transport trailer side walls and those from cattle hide samples within the packing plant.     

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.     

Incidence, duration, and prevalence of Escherichia coli O157:H7 fecal shedding by feedlot cattle during the finishing period

The objective was to describe variability in prevalence, incidence, and duration of fecal shedding of naturally occurring E. coli O157:H7 by a group of feedlot cattle over time. One hundred steers, randomly assigned to 10 pens, were fed a high-concentrate finishing diet for 136 days (19 weeks). Rectal feces from each animal were tested for E. coli O157:H7 every week for 19 weeks. E. coli O157:H7 was recovered from each animal that completed the study and was detected from at least one animal every week. Average pen prevalence of cattle shedding E. coli O157:H7 varied significantly over time (P < 0.0001) and across pens (P < 0.0001), ranging from 1 to 80%. Pairwise comparisons of mean pen prevalence of E. coli O157:H7 between weeks and estimation of the predicted probability of an incident case of E. coli O157:H7 over time allowed the definition of three distinct phases--namely, the preepidemic, epidemic, and postepidemic periods. Average pen prevalence varied significantly over time (P < 0.01) and across pens (P < 0.001) for all time periods. The odds of an incident case were significantly greater during epidemic and postepidemic periods relative to the preepidemic period (P = 0.0002 and P = 0.03, respectively). Duration of infection was significantly longer for first or second infections that began during epidemic or postepidemic periods relative to the preepidemic period (P < 0.001). Both incidence and duration of shedding peaked during the epidemic period. Pen-level prevalence of cattle shedding E. coli O157:H7 was affected by both incidence and duration of shedding and could be explained by time- or pen-dependent risk factors, or both.     

Naturally colonized beef cattle populations fed combinations of yeast culture and an ionophore in finishing diets containing dried distiller's grains with solubles had similar fecal shedding of Escherichia coli O157:H7

Beef steers (n = 252) were used to evaluate the effects of dietary supplement on fecal shedding of Escherichia coli O157:H7. Seven pens of 9 steers (63 steers per treatment) were fed diets supplemented with or without yeast culture (YC) or monensin (MON) and their combination (YC × MON). YC and MON were offered at 2.8 g/kg and 33 mg/kg of dry matter intake, respectively. Environmental sponge samples (from each pen floor, feed bunk, and water trough) were collected on day 0. Rectal fecal grab samples were collected on days 0, 28, 56, 84, 110, and 125. Samples were collected and pooled by pen and analyzed for presumptive E. coli O157:H7 colonies, which were confirmed by a multiplex PCR assay and characterized by pulsed-field gel electrophoresis (PFGE) typing. On day 0, E. coli O157:H7 was detected in 7.0% of feed bunk samples and 14.3% of pen floor samples but in none of the water trough samples. The 71.4% prevalence of E. coli O157:H7 in fecal samples on day 0 decreased significantly (P < 0.05) over time. E. coli O157:H7 fecal shedding was not associated with dietary treatment (P > 0.05); however, in cattle fed YC and YC × MON fecal shedding was 0% by day 28. Eight Xba I PFGE subtypes were identified, and a predominant subtype and three closely related subtypes (differing by three or fewer bands) accounted for 78.7% of environmental and fecal isolates characterized. Results from this study indicate that feeding YC to cattle may numerically decrease but not eliminate fecal shedding of E. coli O157:H7 at the onset of treatment and that certain E. coli O157 subtypes found in the feedlot environment may persist in feedlot cattle.     

Monitoring Escherichia coli O157:H7 in inoculated and naturally colonized feedlot cattle and their environment

On-farm methods of monitoring Escherichia coli O157:H7 were assessed in 30 experimentally inoculated steers housed in four pens over a 12-week period and in 202,878 naturally colonized feedlot cattle housed in 1,160 pens on four commercial Alberta feedlots over a 1-year period. In the challenge study, yearling steers were experimentally inoculated with 10(10) CFU of a four-strain mixture of nalidixic acid-resistant E. coli O157:H7. After inoculation, shedding of E. coli O157:H7 was monitored weekly by collecting rectal fecal samples (FEC), oral swabs (ORL), pooled fecal pats (PAT), manila ropes (ROP) orally accessed for 4 h, feed samples, water, and water bowl interface. Collection of FEC from all animals per pen provided superior isolation (P < 0.01) of E. coli O157:H7 compared with other methods, although labor and animal restraint requirements for fecal sample collection were high. When one sample was collected per pen of animals, E. coli O157:H7 was more likely to be detected from the ROP than from the FEC, PAT, or ORL (P < 0.001). In the commercial feedlot study, samples were limited to ROP and PAT, and E. coli O157:H7 was isolated in 18.8% of PAT and 6.8% of ROP samples. However, for animals that had been resident in the feedlot pen for at least 1 month, isolation of E. coli O157:H7 from ROP was not different from that from PAT (P = 0.35). Pens of animals on feed for <30 days were six times more likely to shed E. coli O157:H7 than were animals on feed for >30 days. However, change in diet did not affect shedding of the organism (P > 0.23) provided that animals had acclimated to the feedlot for 1 month or longer. Findings from this study indicate the importance of introduction of mitigation strategies early in the feeding period to reduce transference and the degree to which E. coli O157:H7 is shed into the environment.     

Ascophyllum nodosum supplementation: a preharvest intervention for reducing Escherichia coli O157:H7 and Salmonella spp. in feedlot steers

Ascophyllum nodosum (Tasco-14) decreased the prevalence of enterohemorrhagic Escherichia coli (EHEC) O157:H7 in animals fed prior to harvest. Tasco-14 was supplemented on a 2% dry matter basis 14 days prior to harvest to determine its effects on EHEC and Salmonella spp. prevalence. Two hundred mixed crossbred steers and heifers (Bos indicus x Bos taurus), in a large commercial finishing facility, served as experimental units. Treatment (TRT, n = 100) animals received a steam-rolled corn-based diet containing 2% Tasco-14 on a dry matter basis, and control (CON, n = 100) animals received only the steam-rolled corn-based diet. Hide swabs and fecal samples were obtained for EHEC and Salmonella spp. evaluations. Animals were sampled 1 day prior to (d - 1) the feeding of Tasco-14 and immediately following exsanguinations. The prevalence of EHEC O157 on hide swabs and in fecal samples (P = 0.0001 and P < 0.0001, respectively) and the prevalence of EHEC O157:H7 on hide swabs and in fecal samples (P < 0.0001 and P < 0.0001, respectively) was reduced by 33 and 36% from d - 1 levels on TRT hide swabs and by 9 and 11% in TRT fecal samples. The prevalence of EHEC O157 and EHEC O157:H7 was reduced by 33 and 36% from d - 1 levels on TRT hide swabs and by 9 and 11% in TRT fecal samples. The prevalence of Salmonella spp. on hide swabs did not change for TRT animals (P = 0.64). CON animals showed an increase in Salmonella spp. prevalence (P < 0.0001) from d - 1 feeding levels on hide swabs. The prevalence of Salmonella spp. increased in both TRT and CON fecal samples when compared to d - 1 levels (P = 0.002). However, TRT samples exhibited a lower (P < 0.05) postfeeding prevalence of Salmonella spp. in fecal samples than did CON samples. Results from this study indicate that 2% Tasco-14 supplementation in feedlot cattle diets reduces EHEC O157 and EHEC O157:H7 prevalence on hide swabs and in fecal samples and may suppress increases in Salmonella spp.     

Comparative effect of direct-fed microbials on fecal shedding of Escherichia coli O157:H7 and Salmonella in naturally infected feedlot cattle

The effect of direct-fed microbials (DFM) on fecal shedding of Escherichia coli O157:H7 and Salmonella in naturally infected feedlot cattle was evaluated in a clinical trial involving 138 feedlot steers. Following standard laboratory methods, fecal samples collected from steers were evaluated for change in the detectable levels of E. coli O157:H7 and Salmonella shed in feces after DFM treatment. Sampling of steers was carried out every 3 weeks for 84 days. A significant reduction (32%) in fecal shedding of E. coli O157:H7 (P < 0.001), but not Salmonella (P = 0.24), was observed among the treatment steers compared with the control group during finishing. The probability of recovery of E. coli O157:H7 from the feces of treated and control steers was 34.0 and 66.0%, respectively. Steers placed on DFM supplement were almost three times less likely to shed E. coli O157:H7 (odds ratio, 0.36; 95% confidence interval, 0.25 to 0.53; P < 0.001) in their feces as opposed to their control counterparts. The probability of recovery of Salmonella from the feces of the control (14.0%) and the treated (11.3%) steers was similar. However, the DFM significantly reduced probability of new infections with Salmonella among DFM-treated cattle compared with controls (nontreated ones). It appears that DFM as applied in our study are capable of significantly reducing fecal shedding of E. coli O157:H7 in naturally infected cattle but not Salmonella. The factors responsible for the observed difference in the effects of DFM on E. coli O157:H7 and Salmonella warrants further investigation.     

Development of an experimental model to assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder within a feedlot environment

This study was conducted to develop an experimental model that could assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder (>10(4) CFU/g of feces) within a feedlot environment. The day before the study began, 48 steers that had been negative for E. coli O157:H7 in feces for three consecutive weeks were sorted into three treatment groups, with two replicate pens per treatment and 8 steers per pen. Steers within the pens (20.50 by 10.75 m) were exposed to control feces or feces inoculated with two levels of a mixture of five strains of nalidixic acid-resistant E. coli O157:H7 (low level, 10(2) CFU/g; high level, 10(5) CFU/g). Five 300-g fecal pats were introduced into the pens twice daily (10:00 a.m. and 2:30 p.m.) on days 0 through 6 and days 14 through 20. Pats were placed in the pen at random locations to mimic defecation of a steer within the pen. Fecal grab samples, hide swab samples (500-cm2 area of the rump), natural fecal pat samples (freshly voided), and rope samples (1.22-m-long manila rope) where obtained at multiple times during the 49-day trial to evaluate the spread of nalidixic acid-resistant E. coli O157:H7 throughout the feedlot environment and among penmates. Immunomagnetic separation and selective media were used to detect E. coli O157:H7. Nalidixic acid-resistant E. coli O157:H7 was detected in 13 high-level treatment fecal grab samples, 7 high-level treatment hide swab samples, 1 low-level hide swab sample, and 2 high-level rope samples. For both fecal grab and hide swab samples, the overall prevalence of E. coli O157:H7 in the high-level group was greater (P < 0.01) than that for the pooled low-level and control groups. Addition of inoculated fecal pats to pens increased transmission of E. coli O157:H7 among penmates, but cattle that acquired E. coli O157:H7 shed the bacterium for only a short time at low levels. Transmission of E. coli O157:H7 from the feces of super shedders to naive penmates may contribute to the observed transient nature of shedding of E. coli O157:H7 among feedlot cattle.     

Effect of a vaccine product containing type III secreted proteins on the probability of Escherichia coli O157:H7 fecal shedding and mucosal colonization in feedlot cattle

Preharvest intervention strategies to reduce Escherichia coli O157:H7 in cattle have been sought as a means to reduce human foodborne illness. A blinded clinical trial was conducted to test the effect of a vaccine product on the probability that feedlot steers, under conditions of natural exposure, shed E. coli O157:H7 in feces, are colonized by this organism in the terminal rectum, or develop a humoral response to the respective antigens. Steers (n = 288) were assigned randomly to 36 pens (eight head per pen), and pens were randomized to vaccination treatment in a balanced fashion within six dietary treatments of an unrelated nutrition study. Treatments included vaccination or placebo (three doses at 3-week intervals). Fecal samples for culture (n = 1,410) were collected from the rectum of each steer on pretreatment day 0 and posttreatment days 14, 28, 42, and 56. Terminal rectum mucosal (TRM) cells were aseptically collected for culture at harvest (day 57 posttreatment) by scraping the mucosa 3.0 to 5.5 cm proximal to the rectoanal junction. E. coli O157:H7 was isolated and identified with selective enrichment, immunomagnetic separation, and PCR confirmation. Vaccinated cattle were 98.3% less likely to be colonized by E. coli O157:H7 in TRM cells (odds ratio = 0.014, P < 0.0001). Diet was also associated with the probability of cattle being colonized (P = 0.04). Vaccinated cattle demonstrated significant humoral responses to Tir and O157 lipopolysaccharide. These results provide evidence that this vaccine product reduces E. coli O157:H7 colonization of the terminal rectum of feedlot beef cattle under conditions of natural exposure, a first step in its evaluation as an effective intervention for food and environmental safety.     

Impact of reducing the level of wet distillers grains fed to cattle prior to harvest on prevalence and levels of Escherichia coli O157:H7 in feces and on hides

Cattle fed finishing diets with wet distillers grains with solubles (WDGS) have been shown to harbor increased Escherichia coli O157:H7 populations in the feces and on the hides. To determine if feeding a lower level of WDGS at the end of the feeding period reduces E. coli O157:H7 load at harvest, 608 heifers were sorted into one of five treatments and fed 0, 40, or 70% WDGS (dry matter basis). For three of the treatments, WDGS was reduced midway through the study. Treatment 0W0W heifers (positive control) were fed a corn grain-based diet continuously, and 40W40W heifers (negative control) were fed 40% WDGS continuously. Heifers subjected to treatments 40W0W, 40W15W, and 70W15W were fed either 40 or 70% WDGS for the first 56 days and switched to 0 or 15% WDGS, respectively, for the last 56 days. Prior to the switch in diets, animals fed diets with 40 or 70% had higher prevalence and percent enumerable fecal samples for E. coli O157:H7. After the dietary switch, animals fed 40W0W, 40W15W, and 70W15W diets had fecal prevalence and percent enumerable samples (33.4 and 6.3%, 31.0 and 9.7%, and 34.9 and 8.4%, respectively) similar to those of animals fed 0W0W diets (10.2 and 3.2%, respectively; P > 0.05), whereas animals fed 40W40W had the highest fecal prevalence and percent enumerable samples (70.1 and 29.2%, respectively; P < 0.05). Similar relationships between the treatments were observed for hide samples. Time after dietary switch was important, as animals fed lower levels had significantly lower fecal prevalence and percent enumerable samples after 56 days, but not after 28 days. The study indicates that cattle can be switched to lower levels of dietary WDGS (15% or less) 56 days prior to harvest to significantly reduce E. coli O157:H7 in feces and on hides.     

Pathogenicity of enterohemorrhagic Escherichia coli in neonatal calves and evaluation of fecal shedding by treatment with probiotic Escherichia coli

The pathogenicity and fecal shedding of enterohemorrhagic Escherichia coli (EHEC) O26:H11, O111:NM, and O157:H7 were compared in calves (< 1 week of age) with or without prior treatment with probiotic bacteria (competitive exclusion E. coli). Three groups of 12 to 14 calves were used for these treatments. Half of the calves in each group were perorally administered 10(10) CFU of probiotic bacteria per calf, and, 2 days thereafter, 10(8) CFU of a five-strain mixture with one of the three EHEC serotypes per calf were administered to each calf. None of the EHEC serotypes caused clinical disease,and neither gross nor microscopic lesions attributable to EHEC were detected in control or probiotic-treated calves at necropsy. In calves administered E. coli O157:H7, fecal shedding was greatly reduced (> 6 log10 CFU/g) by 8 days after administration, and there was no significant difference (P > 0.05) in fecal shedding of E. coli O157:H7 between probiotic-treated and untreated control groups at that time. In contrast, control calves perorally administered E. coil of serotypes O111:NM or O26:H11 continued to shed substantial populations (10(2.1) to 10(6) CFU/g of feces and 10(2.5) to 10(4.9) CFU/g of feces, respectively) throughout 7 days postadministration of EHEC. In both groups administered either E. coli O111:NM or O26:H11, significantly less (P < 0.05) EHEC was isolated from feces at 7 days postadministration of EHEC and at necropsy from theprobiotic-treated group than from the untreated control group. Overall, neonatal calves shed in the feces from 1 to 7 days following peroral administration of EHEC greater populations of E. coli O111:NM and O26:H111 than E. coli O157:H7. In addition, treatment of calves with probiotic E. coli reduced fecal shedding of E. coli O111:NM and O26:H11 in most calves.     

The effect of different grain diets on fecal shedding of Escherichia coli O157:H7 by steers

Three groups of six yearling steers (three rumen fistulated plus three nonfistulated) fed one of three different grain diets (85% cracked corn, 15% whole cottonseed and 70% barley, or 85% barley) were inoculated with 10(10) CFU of Escherichia coli O157:H7 strain 3081, and the presence of the inoculated strain was followed in the rumen fluid and feces for a 10-week period. E. coli O157:H7 was rapidly eliminated from the rumen of the animals on all three diets but persisted in the feces of some animals up to 67 days after inoculation, suggesting that the bovine hindgut is the site of E. coli O157:H7 persistence. A significant difference existed in the levels of E. coli O157:H7 shed by the animals among diets on days 5, 7, 49, and 63 after inoculation (P < 0.05). No significant difference was found between the levels shed among diets on days 9 through 42 and on day 67 (P > 0.05). The number of animals that were culture positive for E. coli O157:H7 strain 3081 during the 10-week period was significantly higher for the barley fed group (72 of 114 samplings) as opposed to the corn fed group (44 of 114 samplings) (P < 0.005) and the cottonseed and barley fed group (57 of 114 samplings) (P < 0.05). The fecal pH of the animals fed the corn diet was significantly lower (P < 0.05) than the fecal pH of the animals fed the cottonseed and barley and barley diets, likely resulting in a less suitable environment for E. coli O157:H7 in the hindgut of the corn fed animals. E. coli O157:H7 strain 3081 was present in 3 of 30 (corn, 1 of 10; cottonseed, 1 of 10; barley, 1 of 10) animal drinking water samples, 3 of 30 (corn, 1 of 10; cottonseed, 0 of 10; barley, 2 of 10) water trough biofilm swabs, 5 of 30 (corn, 0 of 10; cottonseed, 2 of 10; barley, 3 of 10) feed samples, and 30 of 30 manure samples taken from the pens during the entire experimental period. Mouth swabs of the steers were also culture positive for E. coli O157:H7 strain 3081 in 30 of 180 samples (corn, 7 of 60; cottonseed, 4 of 60; barley, 19 of 60) taken during the 10-week period. Minimizing environmental dissemination of E. coli O157:H7 in conjunction with diet modification may reduce numbers of E. coli O157:H7-positive cattle.     

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.     

Efficacy of dose regimen and observation of herd immunity from a vaccine against Escherichia coli O157:H7 for feedlot cattle

A clinical trial was conducted to test the effect of a vaccine product containing type III secreted proteins of Escherichia coli O157:H7 on the probability that feedlot steers shed E. coli O157:H7 in feces. Six hundred eight same-source steers were utilized. Of these, 480 steers were assigned randomly to 60 pens (eight head per pen) and to one of four vaccination treatments (120 cattle per treatment, two head per treatment per pen). The four treatments were (i) no vaccination; (ii) one dose, vaccinated once at reimplant (day 42); (iii) two doses, vaccinated on arrival (day 0) and again at reimplant (day 42); and (iv) three doses, vaccinated on arrival (day 0), on day 21, and again at reimplant (day 42). The remaining 128 steers were assigned randomly to 12 pens within the same feedlot to serve as unvaccinated external controls. The probability of detecting E. coli O157:H7 among cattle receiving different doses of vaccine was compared with that of unvaccinated external control cattle, accounting for clustering by repeated measures, block, and pen and fixed effects of vaccine, corn product, and test period. Vaccine efficacy of receiving one, two, and three doses of vaccine was 68, 66, and 73%, respectively, compared with cattle in pens not receiving vaccine. Cattle receiving three doses of vaccine were significantly less likely to shed E. coli O157:H7 than unvaccinated cattle within the same pen. Unvaccinated cattle housed with vaccinated cattle were 59% less likely to shed E. coli O157:H7 than cattle in pens not receiving vaccine, likely because they benefited from herd immunity. This study supports the hypothesis that vaccination with this vaccine product effectively reduces the probability for cattle to shed E. coli O157:H7. There was no indication that the vaccine affected performance or carcass quality. In addition, we found that vaccinating a majority of cattle within a pen offered a significant protective effect (herd immunity) to unvaccinated cattle within the same pen.