Escherichia coli O157:H7 in Environments of Culture-Positive Cattle

Outbreaks of Escherichia coli O157:H7 disease associated with animal exhibits have been reported with increasing frequency. Transmission can occur through contact with contaminated haircoats, bedding, farm structures, or water. We investigated the distribution and survival of E. coli O157:H7 in the immediate environments of individually housed, experimentally inoculated cattle by systematically culturing feed, bedding, water, haircoat, and feed bunk walls for E. coli O157:H7 for 3 months. Cedar chip bedding was the most frequently culture-positive environmental sample tested (27/96 or 28.15%). Among these, 12 (44.0%) of positive bedding samples were collected when the penned animal was fecal culture negative. Survival of E. coli O157:H7 in experimentally inoculated cedar chip bedding and in grass hay feed was determined at different temperatures. Survival was longest in feed at room temperature (60 days), but bacterial counts decreased over time. The possibility that urine plays a role in the environmental survival of E. coli O157:H7 was investigated. Cedar chip bedding moistened with sterile water or bovine urine was inoculated with E. coli O157:H7. Bedding moistened with urine supported growth of E. coli O157:H7, whereas inoculated bedding moistened with only water yielded decreasing numbers of bacteria over time. The findings that environmental samples were frequently positive for E. coli O157:H7 at times when animals were culture negative and that urine provided a substrate for E. coli O157:H7 growth have implications for understanding the on-farm ecology of this pathogen and for the safety of ruminant animal exhibits, particularly petting zoos and farms where children may enter animal pens.     

Shedding of Escherichia coli O157:H7 in dairy cattle housed in a confined environment following waterborne inoculation

A study of Escherichia coli O157:H7 transmission and shedding was conducted with bull calves housed in individual pens within a confined environment. For comparative purposes, the numbers and duration of E. coli O157:H7 shedding in naturally infected calves were monitored after a single purchased calf (calf 156) tested positive prior to inoculation. During the next 8 days, the calves in adjacent pens and a pen directly across a walkway from calf 156 began to shed this serotype O157:H7 strain. Five of the eight calves in this room shed this O157:H7 strain at some time during the following 8 weeks. The numbers of E. coli O157:H7 isolates shed in these calves varied from 60 to 10(5) CFU/g of feces, and the duration of shedding ranged from 17 to >31 days. The genomic DNAs from isolates recovered from these calves were indistinguishable when compared by using XbaI digestion and pulsed-field gel electrophoresis. Inoculation of calves with 1 liter of water containing ca. 10(3) to 10(4) CFU of E. coli O157:H7/ml resulted in shedding in 10 of 12 calves (trial 1, 4 of 4 calves; trial 2, 6 of 8 calves). The inoculated calves shed the inoculation strain (FRIK 1275) as early as 24 h after administration. The duration of shedding varied from 18 to >43 days at levels from 10(2) to 10(6) CFU/g of feces. The numbers of doses necessary to initiate shedding varied among calves, and two calves in trial 2 never shed FRIK 1275 after four doses (ca. 10(6) CFU per dose). Results from this study confirm previous reports of animal-to-animal and waterborne dissemination of E. coli O157:H7 and highlight the need for an effective water treatment to reduce the spread of this pathogen in cattle.     

Waterborne Escherichia coli O157

The waterborne route of Vero cytotoxin-producing E. coli (VTEC) O157 infection was first suggested in two unconnected human cases in 1985. Since then, waterborne VTEC O157 has been identified in sporadic cases and in outbreaks of illness. Recreational waters, private and municipal supplies have been implicated from microbiological, environmental and epidemiological studies of cases. In addition, a research cohort study of farm workers identified exposure to private water supplies as a risk factor for having antibodies to E. coli O157. Sources of contamination are thought to be animal and human faeces or sewage. The presence of low numbers of target organisms in water makes microbiological confirmation difficult, therefore epidemiological evidence has been essential in outbreak investigations. Despite the potential for contamination of water with VTEC O157, waterborne infection is relatively rare largely due to the susceptibility of the organism to water treatment processes. This paper presents the evidence for waterborne VTEC O157 infection, considering current microbiological, environmental and particularly epidemiological information.     

Prevalence of Escherichia coli O157:H7 in Gallbladders of Beef Cattle

Gallbladders and rectal contents were collected from cattle (n = 933) at slaughter to determine whether the gallbladder harbors Escherichia coli O157:H7. Both gallbladder mucosal swabs and homogenized mucosal tissues were used for isolation. Only five gallbladders (0.54%) were positive for E. coli O157:H7. Fecal prevalence averaged 7.1%; however, none of the cattle that had E. coli O157:H7 in the gallbladder was positive for E. coli O157:H7 in feces. Therefore, the gallbladder does not appear to be a common site of colonization for E. coli O157:H7 in beef cattle.     

Association of Escherichia coli O157:H7 with Houseflies on a Cattle Farm

The ecology of Escherichia coli O157:H7 is not well understood. The aims of this study were to determine the prevalence of and characterize E. coli O157:H7 associated with houseflies (HF). Musca domestica L. HF (n = 3,440) were collected from two sites on a cattle farm over a 4-month period and processed individually for E. coli O157:H7 isolation and quantification. The prevalence of E. coli O157:H7 was 2.9 and 1.4% in HF collected from feed bunks and a cattle feed storage shed, respectively. E. coli O157:H7 counts ranged from 3.0 × 10¹ to 1.5 × 10⁵ CFU among the positive HF. PCR analysis of the E. coli O157:H7 isolates revealed that 90.4, 99.2, 99.2, and 100% of them (n = 125) possessed the stx1, stx2, eaeA, and fliC genes, respectively. Large populations of HF on cattle farms may play a role in the dissemination of E. coli O157:H7 among animals and to the surrounding environment.     

Effect of Ractopamine HCl Supplementation on Fecal Shedding of Escherichia coli O157:H7 and Salmonella in Feedlot Cattle

The effects of the β-agonist ractopamine, recently approved for use in feedlot cattle to improve carcass quality and performance, on fecal shedding Escherichia coli O157:H7 and Salmonella in feedlot cattle was examined. In the first study, 20 feedlot steers and heifers were randomly assigned to receive ractopamine or no ractopamine (control) by way of oral bolus for 28 days. Fecal samples were collected daily, and shedding of E. coli O157:H7 determined. When examined during the entire 28-day experimental period, ractopamine decreased (P = 0.0006) the percentage of cattle shedding E. coli O157:H7 (58% vs. 42% for control and ractopamine treatments, respectively). A second study was conducted in a commercial feedlot facility in the southwestern United States. Eighteen pens of cross-bred beef heifers (approximately 100 head/pen and 9 pens/treatment) were randomly assigned to receive either 0 (control) or 200 mg ractopamine/head·d^–1. Fresh fecal samples (30/pen) were collected off the pen floor before ractopamine supplementation and again after approximately 28 days of ractopamine supplementation (within a few days of slaughter); the samples were cultured for E. coli O157:H7 and Salmonella. The percentage of animals shedding E. coli O157:H7 was decreased when data were pooled across replicates (P = 0.05) in ractopamine-treated cattle compared with controls. The percentage of animals shedding Salmonella tended to be higher (P = 0.08) with the ractopamine treatment when data were pooled across replicates. Although further research is required to confirm these results, the potential food safety implications of this research are intriguing. Mention of trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the United States Drug Administration and does not imply its approval to the exclusion of other products that may be suitable.     

Differences in Colonization and Shedding Patterns after Oral Challenge of Cattle with Three Escherichia coli O157:H7 Strains

Experimental oral challenge studies with three different genotypes of Escherichia coli O157:H7 were conducted in cattle to determine the genotype-specific variability in shedding frequencies and concentrations and the frequency and extent of contamination of the environment. The results indicated that the E. coli O157:H7 genotype and ecological origin maybe important factors for the occurrence and concentration in the cattle host. Four groups of six young Holstein steers each were orally challenged with 10⁶ CFU of one of three E. coli O157:H7 strains: FRIK 47 (groups 1 and 2), FRIK 1641 (group 3), and FRIK 2533 (group 4). Recto-anal mucosal swabs (RAMS) and environmental samples were taken on alternate days over 30 days. The numbers of E. coli O157:H7 cells and generic E. coli cells per sample were determined. Also, the presence and absence of 28 gene targets were determined for 2,411 isolates using high-throughput real-time PCR. Over the study period, strains FRIK 47, FRIK 1641, and FRIK 2533 were detected in 52%, 42%, and 2% of RAMS, respectively. Environmental detection of the challenge strains was found mainly in samples of the hides and pen floors, with strains FRIK 47, FRIK 1641, and FRIK 2533 detected in 22%, 27%, and 0% of environmental samples, respectively. Based on the panel of 28 gene targets, genotypes of enterohemorrhagic E. coli (EHEC) and generic E. coli from the experimental samples were clustered into three subgroups. In conclusion, the results suggested that the type and intensity of measures to control this pathogen at the preharvest level may need to be strain specific.     

Effect of Cattle Diet on Escherichia coli O157:H7 Acid Resistance

The duration of shedding of Escherichia coli O157 isolates by hay-fed and grain-fed steers experimentally inoculated with E. coli O157:H7 was compared, as well as the acid resistance of the bacteria. The hay-fed animals shed E. coli O157 longer than the grain-fed animals, and irrespective of diet, these bacteria were equally acid resistant. Feeding cattle hay may increase human infections with E. coli O157:H7.     

Characterization of Escherichia coli O157:H7 Strains Isolated from Supershedding Cattle

Previous reports have indicated that a small proportion of cattle shedding high levels of Escherichia coli O157:H7 is the main source for transmission of this organism between animals. Cattle achieving a fecal shedding status of 10⁴ CFU of E. coli O157:H7/gram or greater are now referred to as supershedders. The aim of this study was to investigate the contribution of E. coli O157:H7 strain type to supershedding and to determine if supershedding was restricted to a specific set of E. coli O157:H7 strains. Fecal swabs (n = 5,086) were collected from cattle at feedlots or during harvest. Supershedders constituted 2.0% of the bovine population tested. Supershedder isolates were characterized by pulsed-field gel electrophoresis (PFGE), phage typing, lineage-specific polymorphism assay (LSPA), Stx-associated bacteriophage insertion (SBI) site determination, and variant analysis of Shiga toxin, tir, and antiterminator Q genes. Isolates representing 52 unique PFGE patterns, 19 phage types, and 12 SBI clusters were obtained from supershedding cattle, indicating that there is no clustering to E. coli O157:H7 genotypes responsible for supershedding. While being isolated directly from cattle, this strain set tended to have higher frequencies of traits associated with human clinical isolates than previously collected bovine isolates with respect to lineage and tir allele, but not for SBI cluster and Q type. We conclude that no exclusive genotype was identified that was common to all supershedder isolates.     

Effect of Dietary Stress on Fecal Shedding of Escherichia coli O157:H7 in Calves

Two groups of calves were subjected to dietary stress by withholding of food beginning 1 or 14 days after inoculation with 10¹⁰ CFU of Escherichia coli O157:H7. Following treatment, neither group had a significant increase in fecal shedding of E. coli O157:H7. A third group of calves had food withheld for 48 h prior to inoculation with 10⁷ CFU of E. coli O157:H7. These calves were more susceptible to infection and shed significantly more E. coli O157:H7 organisms than calves maintained on a normal diet.     

Role of rpoS in Acid Resistance and Fecal Shedding of Escherichia coli O157:H7

Acid resistance (AR) is important to survival of Escherichia coli O157:H7 in acidic foods and may play a role during passage through the bovine host. In this study, we examined the role in AR of the rpoS-encoded global stress response regulator ς^S and its effect on shedding of E. coli O157:H7 in mice and calves. When assayed for each of the three AR systems identified in E. coli, an rpoS mutant (rpoS::pRR10) of E. coli O157:H7 lacked the glucose-repressed system and possessed reduced levels of both the arginine- and glutamate-dependent AR systems. After administration of the rpoS mutant and the wild-type strain (ATCC 43895) to ICR mice at doses ranging from 10¹ to 10⁴ CFU, we found the wild-type strain in feces of mice given lower doses (10² versus 10³ CFU) and at a greater frequency (80% versus 13%) than the mutant strain. The reduction in passage of the rpoS mutant was due to decreased AR, as administration of the mutant in 0.05 M phosphate buffer facilitated passage and increased the frequency of recovery in feces from 27 to 67% at a dose of 10⁴ CFU. Enumeration of E. coli O157:H7 in feces from calves inoculated with an equal mixture of the wild-type strain and the rpoS mutant demonstrated shedding of the mutant to be 10- to 100-fold lower than wild-type numbers. This difference in shedding between the wild-type strain and the rpoS mutant was statistically significant (P ≤ 0.05). Thus, ς^S appears to play a role in E. coli O157:H7 passage in mice and shedding from calves, possibly by inducing expression of the glucose-repressed RpoS-dependent AR determinant and thus increasing resistance to gastrointestinal stress. These findings may provide clues for future efforts aimed at reducing or eliminating this pathogen from cattle herds.     

Differing Populations of Endemic Bacteriophages in Cattle Shedding High and Low Numbers of Escherichia coli O157:H7 Bacteria in Feces

The objectives of this study were to identify endemic bacteriophages (phages) in the feedlot environment and determine relationships of these phages to Escherichia coli O157:H7 from cattle shedding high and low numbers of naturally occurring E. coli O157:H7. Angus crossbred steers were purchased from a southern Alberta (Canada) feedlot where cattle excreting ≥10⁴ CFU · g⁻¹ of E. coli O157:H7 in feces at a single time point were identified as supershedders (SS; n = 6), and cattle excreting <10⁴ CFU · g⁻¹ of feces were identified as low shedders (LS; n = 5). Fecal pats or fecal grabs were collected daily from individual cattle for 5 weeks. E. coli O157:H7 in feces was detected by immunomagnetic separation and enumerated by direct plating, and phages were isolated using short- and overnight-enrichment methods. The total prevalence of E. coli O157:H7 isolated from feces was 14.4% and did not differ between LS and SS (P = 0.972). The total prevalence of phages was higher in the LS group (20.9%) than in the SS group (8.3%; P = 0.01). Based on genome size estimated by pulsed-field gel electrophoresis and morphology determined by transmission electron microscopy, T4- and O1-like phages of Myoviridae and T1-like phage of Siphoviridae were isolated. Compared to T1- and O1-like phages, T4-like phages exhibited a broad host range and strong lytic capability when targeting E. coli O157:H7. Moreover, the T4-like phages were more frequently isolated from feces of LS than SS, suggesting that endemic phages may impact the shedding dynamics of E. coli O157:H7 in cattle.     

Prevalence of Escherichia coli O157:H7 in Organically and Naturally Raised Beef Cattle

We determined the prevalence of Escherichia coli O157:H7 in organically and naturally raised beef cattle at slaughter and compared antibiotic susceptibility profiles of the isolates to those of isolates from conventionally raised beef cattle. The prevalences of E. coli O157:H7 were 14.8 and 14.2% for organically and naturally raised cattle, respectively. No major difference in antibiotic susceptibility patterns among the isolates was observed.Many cattle producers have adopted production methods termed niche marketing to meet consumer demand for safe and healthy beef. The two main niches for beef cattle producers are organic and natural production (3). Organic beef cattle production, regulated by the U.S. Department of Agriculture, requires feeding with certified organic feed (16) and raising cattle without the use of antibiotics, hormones, and other veterinary products (3). Guidelines for producers to label the product as “natural” differ among natural beef programs, and such programs are administered and regulated by the company or organization that owns the brand name rather than the U.S. Department of Agriculture (11). Natural production guidelines often include a complete restriction on the use of antibiotics and growth-promoting hormones, but unlike guidelines for organic production, they allow feed from nonorganic sources (11). Escherichia coli O157:H7 is a major food-borne pathogen that causes outbreaks of hemorrhagic enteritis, which often leads to hemolytic uremic syndrome in children and the elderly (10). Cattle are major reservoirs of E. coli O157:H7, which colonizes the hindgut, specifically the rectoanal mucosal region. Cattle feces are the major source of food and water contamination (10). The impact of organic production methods on the prevalence of food-borne pathogens, including E. coli O157:H7 and Campylobacter spp. in dairy cattle (7, 14) and Campylobacter and Salmonella spp. in chickens (6, 19), has been studied previously. However, there is no published study on the prevalence of E. coli O157:H7 in organically and naturally raised beef cattle. Additionally, nothing is known regarding the effects of organic and natural production methods on the antibiotic susceptibilities of E. coli O157:H7 in beef cattle. Our objectives were to determine the prevalence of E. coli O157:H7 in the feces of organically and naturally raised beef cattle at slaughter and compare the antibiotic susceptibilities of isolates from organically, naturally, and conventionally raised beef cattle.Cattle included in this study were from three types of production systems, organic, natural, and conventional. Organically raised beef cattle were from farms that were certified by the National Organic Program (17). The naturally raised beef cattle were from farms that were certified by the All Natural Source Verified Beef Program (17). The collection of samples from these cattle occurred in an abattoir. Samples from conventionally raised cattle from two feedlots were collected in a different abattoir so that the antibiotic susceptibilities of their isolates could be compared with those of isolates from organically and naturally raised cattle. Fecal samples were obtained by cutting open the rectum and spooning out the contents. The mucosa of the rectum was then rinsed with water until free of visible fecal material and swabbed with a sterile foam-tipped applicator (4). The isolation and identification of E. coli O157 and PCR detection of major virulence genes (eae, stx₁, stx₂, hlyA, and fliC) were carried out as described by Reinstein et al. (13). A subset of 60 isolates, 20 (10 from fecal samples and 10 from rectoanal mucosal swabs [RAMS]) from each production system, was randomly chosen to determine the antibiotic susceptibility patterns by the broth microdilution method (9). The antibiotics (all from Sigma-Aldrich) tested were amikacin, amoxicillin (amoxicilline), ampicillin, apramycin, bacitracin, cefoxitin, ceftazidime, ceftriaxone, cephalothin (cefalotin), chloramphenicol, chlortetracycline, ciprofloxacin, enrofloxacin, erythromycin, florfenicol, gentamicin, kanamycin, lincomycin, monensin, nalidixic acid, neomycin, norfloxacin, novobiocin, oxytetracycline, penicillin, rifampin (rifampicin), spectinomycin, streptomycin, tetracycline, tilmicosin, trimethoprim, tylosin, and vancomycin. The MIC was defined as the lowest concentration of an antibiotic that prevented visible growth of the organism. Each concentration of the antibiotic compound was duplicated in the microtiter plate, and the MIC determination was repeated with a different inoculum preparation. Logistic regression was performed using the PROC GENMOD procedure in the SAS system (SAS Institute, Cary, NC) to compare the prevalences of E. coli O157:H7 (with binomial distribution of outcomes) in fecal samples, RAMS samples, and fecal or RAMS samples (overall animal level prevalence). The MICs of antibiotics for E. coli O157:H7 isolates were analyzed using a nonparametric survival test in the PROC LIFETEST program of SAS to determine the effects of the production system (natural, organic, or conventional). Data were right censored when necessary (when the organism was resistant to the highest concentration evaluated). The Wilcoxon test was utilized to determine the effect of the production system on MICs.Samples from a total of 553, 506, and 322 organically, naturally, and conventionally raised cattle, respectively, were collected. In organically raised cattle, the prevalence of E. coli O157:H7 in fecal samples ranged from 0 to 24.4% across sampling days, with an average of 9.3%, and the prevalence in RAMS ranged from 0 to 30.9%, with an average of 8.7% (Fig. ​(Fig.1).1). In naturally raised cattle, the prevalence of E. coli O157:H7 in fecal samples ranged from 0 to 20.3%, with an average of 7.2%, and the prevalence in RAMS ranged from 0 to 23.8%, with an average of 8.9% (Fig. ​(Fig.1).1). In both organically and naturally raised cattle, the prevalence (total) detected by both sampling methods together was greater (P < 0.05) than the prevalence detected by either method alone (Fig. ​(Fig.1).1). Samples (either feces or RAMS) from 36 (11.2%) of 322 conventionally raised feedlot cattle were culture positive for E. coli O157:H7. The fecal prevalence of E. coli O157:H7 was 6.5%, and the prevalence determined by the RAMS sampling method was 7.1%. Most isolates (66.7% from organically raised beef cattle and 77.8% from naturally raised beef cattle) were positive for eae, stx₂, hlyA, and fliC but negative for stx₁. The stx₂ gene was present in 100 and 95% of isolates from organically and naturally raised cattle, respectively. The prevalences of E. coli O157:H7 that we observed in organically and naturally raised beef cattle were similar to the previously reported prevalence in conventionally raised cattle (1). Our study did not include a statistical comparison of the prevalence data because of a number of differences, particularly in diet, among the organic, natural, and conventional production systems. Organically and naturally raised cattle are either required to graze a pasture or fed a forage-based diet. Although conflicting data exist (1), studies have shown that cattle fed a forage diet have both higher levels and longer durations of fecal shedding of E. coli O157:H7 than cattle fed a grain diet (18).Open in a separate windowFIG. 1.Prevalences of E. coli O157:H7 in organically and naturally raised beef cattle at slaughter. For each production system, bars not labeled with the same letter represent significantly different levels at P of <0.05.None of the tested isolates from the three production systems were susceptible to bacitracin, lincomycin, monensin, novobiocin, tilmicosin, tylosin, and vancomycin (MICs > 50 μg/ml). The MICs of 12 antibiotics (amikacin, apramycin, cefoxitin, ceftriaxone, gentamicin, kanamycin, nalidixic acid, neomycin, penicillin, rifampin, streptomycin, and tetracycline) for isolates collected from different production systems were significantly different (P < 0.05). MICs of gentamicin and neomycin for E. coli O157:H7 isolates from conventionally raised cattle were higher (P < 0.05) than those for isolates from naturally and/or organically raised cattle (Table ​(Table1).1). However, MICs of amikacin, apramycin, cefoxitin, ceftriaxone, kanamycin, nalidixic acid, penicillin, rifampin, and tetracycline for isolates from conventionally fed cattle were lower (P < 0.05) than those for isolates from naturally and/or organically raised cattle (Table ​(Table1).1). Among the 60 isolates tested for antibiotic susceptibilities, 6 isolates (10%) were susceptible to all antibiotics included in the study, excluding the seven antibiotics to which all isolates were resistant. Forty-two isolates (70%) were resistant to one antibiotic (MIC, >50 μg or >50 IU/ml), nine isolates (15%) were resistant to two antibiotics, and two isolates (3%) were resistant to five antibiotics. One isolate from the organically raised cattle group was resistant to 10 (amoxicillin, ampicillin, cefoxitin, cephalothin, chloramphenicol, florfenicol, oxytetracycline, penicillin, streptomycin, and tetracycline) of the 26 antibiotics that were inhibitory to other isolates. We have presented the data as the median MICs for each production system. In some instances, the median values were the same but the actual MIC data differed between production systems. This effect occurred because the data were right censored if isolates were not susceptible at 50 μg or 50 IU/ml. If more isolates from a particular production system than from another are censored, it may lead to statistical differences. This pattern justifies the use of survival analysis for this type of data. There were differences between MICs of many antibiotics (cefoxitin, ceftriaxone, gentamicin, nalidixic acid, neomycin, penicillin, rifampin, and tetracycline) for isolates from organically raised cattle and conventionally raised cattle. Similarly, there were differences between MICs of many antibiotics (amikacin, apramycin, ceftriaxone, kanamycin, nalidixic acid, and rifampin) for isolates from naturally raised cattle and conventionally raised cattle. For many of these antibiotics, MICs for isolates from organically or naturally raised cattle were greater than those for isolates from conventionally raised cattle. Resistance genes can be transferred among the enteric pathogen populations in food animals and humans (8), and it is possible that resistance genes from other bacteria in the gastrointestinal system of cattle may be acquired by E. coli O157:H7. For cattle, heavy metals like copper and zinc, which are also antimicrobial, are included in diets at concentrations in excess of the nutritional requirements, often replacing conventional antibiotics, to achieve growth promotion (5). Feeding with metals also results in the emergence of bacterial populations resistant to metals (5), which in some instances may lead to resistance to antibiotics. Mechanisms of resistance to copper at concentrations above those usually tolerated by normal cellular processes have been found on plasmids linked to resistance to antibiotics in some bacteria (5). Therefore, it is possible that isolates from organically or naturally raised cattle that are not exposed to antibiotics still may become resistant to antibiotics.

TABLE 1.

MICs of antimicrobials for E. coli O157:H7 isolates from conventionally, naturally, and organically raised beef cattle

Escherichia coli O157:H7 Colonization at the Rectoanal Junction of Long-Duration Culture-Positive Cattle

Long-duration consistently Escherichia coli O157:H7 culture-positive cattle were euthanized and necropsied. Tissue and digesta from along the gastrointestinal tract (GIT) were cultured for the bacteria and examined histologically for lymphoid character. E. coli O157:H7 was detected only at the rectoanal junction mucosa and not at any other GIT location.     

Dose-Response Envelope for Escherichia coli O157:H7

Escherichia coli O157:H7 is an emerging food and waterborne pathogen in the U.S. and internationally. The objective of this work was to develop a dose-response model for illness by this organism that bounds the uncertainty in the dose-response relationship. No human clinical trial data are available for E. coli O157:H7, but such data are available for two surrogate pathogens: enteropathogenic E. coli (EPEC) and Shigella dysenteriae. E. coli O157:H7 outbreak data provide an initial estimate of the most likely value of the dose-response relationship within the bounds of an envelope defined by beta-Poisson dose-response models fit to the EPEC and S. dysenteriae data. The most likely value of the median effective dose for E. coli O157:H7 is estimated to be approximately 190[emsp4 ]000 colony forming units (cfu). At a dose level of 100[emsp4 ]cfu, the median response predicted by the model is six percent.     

Longitudinal Study of Escherichia coli O157:H7 Dissemination on Four Dairy Farms in Wisconsin

A 14-month longitudinal study was conducted on four dairy farms (C, H, R, and X) in Wisconsin to ascertain the source(s) and dissemination of Escherichia coli O157:H7. A cohort of 15 heifer calves from each farm were sampled weekly by digital rectal retrieval from birth to a minimum of 7 months of age (range, 7 to 13 months). Over the 14 months of the study, the cohort heifers and other randomly selected cattle from farms C and H tested negative. Farm R had two separate periods of E. coli O157:H7 shedding lasting 4 months (November 1995 to February 1996) and 1 month (July to August 1996), while farm X had at least one positive cohort animal for a 5-month period (May to October 1996). Heifers shed O157:H7 strains in feces for 1 to 16 weeks at levels ranging from 2.0 × 10² to 8.7 × 10⁴ CFU per g. E. coli O157:H7 was also isolated from other noncohort cattle, feed, flies, a pigeon, and water associated with the cohort heifers on farms R and/or X. When present in animal drinking water, E. coli O157:H7 disseminated through the cohort cattle and other cattle that used the water source. E. coli O157:H7 was found in water at <1 to 23 CFU/ml. Genomic subtyping by pulsed-field gel electrophoresis demonstrated that a single O157:H7 strain comprised a majority of the isolates from cohort and noncohort cattle, water, and other positive samples (i.e., from feed, flies, and a pigeon, etc.) on a farm. The isolates from farm R displayed two predominant XbaI restriction endonuclease digestion profiles (REDP), REDP 3 and REDP 7, during the first and second periods of shedding, respectively. Six additional REDP that were ≥89% similar to REDP 3 or REDP 7 were identified among the farm R isolates. Additionally, the REDP of an O157:H7 isolate from a heifer on farm R in 1994 was indistinguishable from REDP 3. Farm X had one O157:H7 strain that predominated (96% of positive samples had strains with REDP 9), and the REDP of an isolate from a heifer in 1994 was indistinguishable from REDP 9. These results suggest that E. coli O157:H7 is disseminated from a common source on farms and that strains can persist in a herd for a 2-year period.     

Clonal Dissemination of Escherichia coli O157:H7 Subtypes among Dairy Farms in Northeast Ohio

To ascertain the extent to which indistinguishable strains of Escherichia coli O157:H7 are shared between farms, molecular characterization was performed on E. coli O157:H7 isolates recovered during a longitudinal study of 20 dairy farms in northeast Ohio. Of the 20 dairy farms sampled, 16 were located in a primary area and 4 were located in two other distant geographical areas. A total of 92 E. coli O157:H7 isolates obtained from bovine fecal samples, water trough sediment samples, free-stall bedding, and wild-bird excreta samples were characterized. Fifty genetic subtypes were observed among the isolates using XbaI and BlnI restriction endonucleases. Most restriction endonuclease digestion profiles (REDPs) were spatially and temporally clustered. However, four REDPs from multiple sources were found to be indistinguishable by pulsed-field gel electrophoresis between four pairs of farms. The geographical distance between farms which shared an indistinguishable E. coli O157:H7 REDP ranged from 9 to 50 km, and the on-farm sources sharing indistinguishable REDPs included cattle and wild bird feces and free-stall bedding. Within the study population, E. coli O157:H7 REDP subtypes were disseminated with considerable frequency among farms in close geographic proximity, and nonbovine sources may contribute to the transmission of this organism between farms.     

Characterization of an Escherichia coli O157:H7 Plasmid O157 Deletion Mutant and Its Survival and Persistence in Cattle

Escherichia coli O157:H7 causes hemorrhagic colitis and hemolytic-uremic syndrome in humans, and its major reservoir is healthy cattle. An F-like 92-kb plasmid, pO157, is found in most E. coli O157:H7 clinical isolates, and pO157 shares sequence similarities with plasmids present in other enterohemorrhagic E. coli serotypes. We compared wild-type (WT) E. coli O157:H7 and an isogenic ΔpO157 mutant for (i) growth rates and antibiotic susceptibilities, (ii) survival in environments with various acidity, salt, or heat conditions, (iii) protein expression, and (iv) survival and persistence in cattle following oral challenge. Growth, metabolic reactions, and antibiotic resistance of the ΔpO157 mutant were indistinguishable from those of its complement and the WT. However, in cell competition assays, the WT was more abundant than the ΔpO157 mutant. The ΔpO157 mutant was more resistant to acidic synthetic bovine gastric fluid and bile than the WT. In vivo, the ΔpO157 mutant survived passage through the bovine gastrointestinal tract better than the WT but, interestingly, did not colonize the bovine rectoanal junction mucosa as well as the WT. Many proteins were differentially expressed between the ΔpO157 mutant and the WT. Proteins from whole-cell lysates and membrane fractions of cell lysates were separated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional gel electrophoresis. Ten differentially expressed ~50-kDa proteins were identified by quadrupole-time of flight mass spectrometry and sequence matching with the peptide fragment database. Most of these proteins, including tryptophanase and glutamate decarboxylase isozymes, were related to survival under salvage conditions, and expression was increased by the deletion of pO157. This suggested that the genes on pO157 regulate some chromosomal genes.