Invited review: effects of diet shifts on Escherichia coli in cattle

Preharvest Management and Postharvest Intervention Strategies to Reduce Escherichia coli Contamination in Goat Meat: A Review

Simple Summary

Goat farms and processing facilities worldwide are primarily small-scale, limited resource operations. Cost-effectiveness and practicality are critical factors to be considered before adopting any pre- and/or post-harvest strategies for pathogen reduction in goat meat. Preharvest management methods in goats that can reduce Escherichia coli in meat include minimizing animal stress, selecting diets and feed deprivation times that can reduce fecal shedding of bacteria, and adding tannin-rich feed supplements. In addition, use of appropriate postharvest nonthermal intervention technologies that can reduce microbial loads in carcasses and meat can extend the shelf-life and marketability of goat meat products. Reducing stress prior to slaughter and using nonthermal intervention methods can result in better meat quality and economic returns for producers.

Abstract

Goat meat is the main source of animal protein in developing countries, particularly in Asia and Africa. Goat meat consumption has also increased in the US in the recent years due to the growing ethnic population. The digestive tract of goat is a natural habitat for Escherichia coli organisms. While researchers have long focused on postharvest intervention strategies to control E. coli outbreaks, recent works have also included preharvest methodologies. In goats, these include minimizing animal stress, manipulating diet a few weeks prior to processing, feeding diets high in tannins, controlling feed deprivation times while preparing for processing, and spray washing goats prior to slaughter. Postharvest intervention methods studied in small ruminant meats have included spray washing using water, organic acids, ozonated water, and electrolyzed water, and the use of ultraviolet (UV) light, pulsed UV-light, sonication, low-voltage electricity, organic oils, and hurdle technologies. These intervention methods show a strong antimicrobial activity and are considered environmentally friendly. However, cost-effectiveness, ease of application, and possible negative effects on meat quality characteristics must be carefully considered before adopting any intervention strategy for a given meat processing operation. As discussed in this review paper, novel pre- and post-harvest intervention methods show significant potential for future applications in goat farms and processing plants.

Continuous Flow-Constructed Wetlands for the Treatment of Swine Waste Water

The microbiological quality of treated waste water is always a concern when waste water is disposed to the environment. However, when treated appropriately, such water can serve many purposes to the general population. Therefore, the treatment and removal of contaminants from swine waste water by continuous flow-constructed wetlands involves complex biological, physical, and chemical processes that may produce better quality water with reduced levels of contaminants. Swine waste contains E. coli populations and other bacterial contaminants originating from swine houses through constructed wetlands, but little is known about E. coli population in swine waste water. To assess the impacts of seasonal variations and the effect of the wetland layout/operations on water quality, E. coli isolates were compared for genetic diversity using repetitive extragenic palindromic polymerase chain reaction (REP-PCR). None of the isolates was confirmed as Shiga toxin producing E. coli O157:H7 (STEC); however, other pathotypes, such as enterotoxigenic E. coli (ETEC) were identified. Using a 90% similarity index from REP-PCR, 69 genotypes out of 421 E. coli isolates were found. Our data showed that the E. coli population was significantly (p = 0.036) higher in November than in March and August in most of the wetland cells. Furthermore, there was a significant (p = 0.001) reduction in E. coli populations from wetland influent to the final effluent. Therefore, the use of continuous flow-constructed wetlands may be a good treatment approach for reducing contaminants from different waste water sources.

Potential pathogens, antimicrobial patterns and genotypic diversity of Escherichia coli isolates in constructed wetlands treating swine wastewater

Escherichia coli populations originating from swine houses through constructed wetlands were analyzed for potential pathogens, antimicrobial susceptibility patterns, and genotypic diversity. Escherichia coli isolates (n = 493) were screened for the presence of the following virulence genes: stx1, stx2 and eae (Shiga toxin-producing E. coli [STEC]), heat-labile enterotoxin (LT) genes and heat stable toxin STa and STb (enterotoxigenic E. coli (ETEC), cytotoxin necrotizing factors 1 and 2 (cnf1 and cnf2 [necrotoxigenic E. coli- NTEC]), as well as O and H antigens, and the presence of the antibiotic resistance genes blaTEM, blaSHV, blaCMY-2, tet A, tet B, tet C, mph(A), aadA, StrA/B, sul1, sul2 and sul3. The commensal strains were further screened for 16 antimicrobials and characterized by BOX AIR-1 PCR for unique genotypes. The highest antibiotic resistance prevalence was for tetracycline, followed by erythromycin, ampicillin, streptomycin, sulfisoxazole and kanamycin. Our data showed that most of the isolates had high distribution of single or multidrug-resistant (MDR) genotypes. Therefore, the occurrence of MDR E. coli in the wetland is a matter of great concern due to possible transfer of resistance genes from nonpathogenic to pathogenic strains or vice versa in the environment.

Bastonetes Gram-negativos aeróbios e anaeróbios facultativos no fluido ruminal de bovinos de corte alimentados em pastagem lignificada e em novilhos com acidose ruminal

Resumo: Objetivou-se analisar a população de bastonetes Gram negativos aeróbios e anaeróbios facultativas no suco ruminal bovinos zebuínos de diferentes categorias, alimentados em pastagem tropical, e de novilhos alimentados com alto teor de grão e sem volumosos. Foram coletados fluido ruminal de 32 vacas, 50 novilhos e 50 bezerros alimentadas em pastagem de Brachiaria spp. e de 20 novilhos com acidose ruminal. Após diluições decimais, amostras foram inoculadas em placas contendo ágar MacConkey a 39°C. Para a identificação dos gêneros mais frequentes foram utilizadas provas bioquímicas. A concentração dessas bactérias não diferiu no ambiente ruminal de vacas, novilhos e bezerros de corte alimentados com pastagem tropical lignificada. Os gêneros mais frequentemente identificados para esses animais foram Escherichia, Enterobacter e Klebsiella. Novilhos alimentados sem volumoso e com acidose apresentaram maior taxa de detecção e maior população dessas bactérias no ambiente ruminal (>6 log/ml) quando comparados aos novilhos alimentados somente em pastagem. A espécie Escherichia coli foi predominante entre as bactérias isoladas do fluido ruminal de novilhos alimentados com dieta com alta concentração de grãos e com acidose (p<0,01). Constatou-se que em bovinos de corte, criados em pastagem tropical lignificada, a população desses microrganismos é baixa no ambiente ruminal e com maior diversidade de gêneros bacterianos. Entretanto em novilhos confinados e alimentos sem volumoso, apresentando acidose ruminal subaguda, ocorre desequilíbrio populacional com aumento da população de E. coli.

Risk factors for Escherichia coli O157 shedding and super-shedding by dairy heifers at pasture

We undertook a longitudinal study within a cohort of 52 dairy heifers maintained under constant management systems and sampled weekly to investigate a comprehensive range of risk factors which may influence shedding or super-shedding of E. coli O157 (detected by direct faecal culture and immunomagnetic separation). E. coli O157 was detected from 416/933 (44.6%) samples (faeces and recto-anal mucosal swabs) and 32 (3.4%) samples enumerated at >10000 c.f.u./g. Weekly point prevalence ranged from 9.4% to 94.3%. Higher temperature (P < 0.001), rainfall (P = 0.02), relative humidity (P < 0.001), pasture growth (P = 0.013) and body score (P = 0.029) were positively associated with increased shedding. Higher rainfall (P < 0.001), hide contamination (P = 0.002) and increased faecal consistency (P = 0.023) were positively associated with super-shedding. Increased solar exposure had a negative effect on both shedding and super-shedding within bivariate analyses but in the final multivariate model for shedding demonstrated a positive effect (P = 0.017). Results suggest that environmental factors are important in E. coli O157 shedding in cattle.

Plane of nutrition x tick burden interaction in cattle: effect on fecal composition

Effective tick management on grazing animals is facilitated by accurate noninvasive detection methods. Fecal analysis provides information about animal health and nutrition. Diet affects fecal composition; stress may do likewise. The constituents in feces that may be affected by tick burdens and in turn affect near-infrared spectra have not been reported. Our objective was to examine the interaction between plane of nutrition and tick burden on fecal composition in cattle. Angus cross steers (n = 28; 194 ± 3.0 kg) were assigned to 1 of 4 treatments (n = 7 per group) in a 2 × 2 factorial arrangement: moderate (14.0 ± 1.0% CP and 60 ± 1.5% TDN) vs. low (9.0 ± 1.0% CP and 58 ± 1.5% TDN) plane of nutrition and control (no tick) vs. tick treatment [infestation of 300 pair of adult Lone Star ticks (Amblyomma americanum) per treated animal]. Fecal samples were collected at approximately 0700 h on d -7, 0, 7, 10, 14, 17, and 21 relative to tick infestation. Fecal constituents measured were DM, OM, pH, Lactobacillus spp., Escherchia coli, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, IgA, and cortisol. Experimental day affected (P < 0.05) all constituents measured. Plane of nutrition affected (P < 0.05) DM, OM, VFA, and IgA. Tick treatment numerically (P = 0.13) reduced cortisol. A multivariate stepwise selection model containing cortisol and E. coli values on d 10 and d 14 accounted for 33% of the variation in daily adult female tick feeding counts across both planes of nutrition (P < 0.07). Within the moderate plane of nutrition, a model containing only cortisol on d 10 and d 14 described 59% of the variation in the number of feeding ticks (P < 0.02). Similarly, a model including cortisol, propionate, isovalerate, and DM at d 10 and d 14 d described 95% of the variation in total feeding ticks in the low plane of nutrition. Of the constituents measured, fecal cortisol offers the best possibility of noninvasively assessing stress by way of a single assay but the presence of ticks would still need to be confirmed visually. Although several constituents measured in this study should exist in sufficient quantity to directly affect near-infrared spectra, none stood out as a clear descriptor of prior observed differences in fecal spectra between tick-treated versus non-tick-treated animals. There were, however, groups of fecal constituents related to daily adult female tick feeding numbers (as a visual estimation of tick stress).

Bacteriophages and their role in food safety

The interest for natural antimicrobial compounds has increased due to alterations in consumer positions towards the use of chemical preservatives in foodstuff and food processing surfaces. Bacteriophages fit in the class of natural antimicrobial and their effectiveness in controlling bacterial pathogens in agro-food industry has led to the development of different phage products already approved by USFDA and USDA. The majority of these products are to be used in farm animals or animal products such as carcasses, meats and also in agricultural and horticultural products. Treatment with specific phages in the food industry can prevent the decay of products and the spread of bacterial diseases and ultimately promote safe environments in animal and plant food production, processing, and handling. This is an overview of recent work carried out with phages as tools to promote food safety, starting with a general introduction describing the prevalence of foodborne pathogens and bacteriophages and a more detailed discussion on the use of phage therapy to prevent and treat experimentally induced infections of animals against the most common foodborne pathogens, the use of phages as biocontrol agents in foods, and also their use as biosanitizers of food contact surfaces.

Interplay between rumen digestive disorders and diet-induced inflammation in dairy cattle

In this review, an overview is provided on the current achievements regarding the interplay between rumen digestive disorders and diet-induced inflammation in dairy cattle. It starts with a review of factors favoring the disturbances in the rumen metabolism, which culminate with development of sub-acute rumen acidosis (SARA). The latter digestive disorder is often linked to greater metabolic stress of gastrointestinal (GI) microbiota and lowered fiber digestion, as well as with disruption of the barrier functions of the GI epithelia, which open the route of deleterious molecules to translocate from the GI lumen into the portal system. A model is suggested to illustrate the mechanisms of the involvement of digestive disorders in the disruption of the host's inner homeostasis leading to activation of acute phase response (APR). The latter is part of multifaceted innate immune and metabolic responses of the host. According to this model, endotoxin, its toxicity, and other metabolic compounds of microbial origin are regarded as important immunogenic components of GI tract, which when favored by disruption of host barriers triggers a systemic APR. Although the activation of an APR is viewed as a protective reaction aiming to reestablish the disturbed homeostasis, the presence of inflammatory state over long periods might be associated with negative consequences for the host. The review concludes that prolonged systemic inflammation can: (1) cause significant changes in the energy and lipid metabolism in different body tissues, (2) lead to the development of refractory states associated with immune suppression and increased susceptibility to various diseases, and (3) artificially increase host's requirements in energy and nutrients, lowering the efficiency of energy and feed use by the animal. The paper emphasizes the critical role that formulation of healthy diets plays for curbing down inflammation and enhancing metabolic health of dairy cows.

Effect of backgrounding and transition diets on fecal concentration and strain types of commensalEscherichia coliin beef cattle

Su, R., Munns, K., Beauchemin, K. A., Schwartzkopf-Genswein, K., Jin-Quan, L., Topp, E. and Sharma, R. 2011. Effect of backgrounding and transition diets on fecal concentration and strain types of commensal Escherichia coli in beef cattle. Can. J. Anim. Sci. 91: 449–458. The aim of the study was to assess the effect of four different backgrounding diets [55% corn silage in combination with 40% of either temper rolled barley-grain, wheat dried distillers' grain, corn dried distillers' grain or millrun (dry matter basis)] and a transition diet containing increasing amount of concentrate (60 to 90%) on fecal Escherichia coli in feedlot heifers. Heifers were fed backgrounding forage based diets for 91 d and then were shifted to a transition diet for an additional 18 d. Strain characterization of E. coli (n=224) was carried out at time time points over 109 d and indicated that heifers fed the barley–grain diet shed higher (P<0.001) total and tetracycline-resistant (Tetr) E. coli in the backgrounding phase. Of the total E. coli examined (n=224), 70.3% showed resistance to one or more of the 14 antimicrobials examined, which increased to 82.3% by day 109. Among the recovered E. coli, 23 phenotypes and 154 pulsed field gel electrophoresis patterns grouped into 38 clusters indicative of extensive E. coli diversity in heifers. Although supplementation of 40% barley-grain was correlated to higher total E. coli shedding in the backgrounding phase, the backgrounding diets did not influence strain clustering. Strains collected during the transition phase clustered more closely than those collected during the backgrounding phase. This increased strain clustering with high concentrate inclusion in the transition diet was observed within 18 d of the transition phase. Our study indicated variations in E. coli shedding rates and strain clustering in relation to time and diet.

Diet-induced bacterial immunogens in the gastrointestinal tract of dairy cows: impacts on immunity and metabolism

Dairy cows are often fed high grain diets to meet the energy demand for high milk production or simply due to a lack of forages at times. As a result, ruminal acidosis, especially subacute ruminal acidosis (SARA), occurs frequently in practical dairy production. When SARA occurs, bacterial endotoxin (or lipopolysaccharide, LPS) is released in the rumen and the large intestine in a large amount. Many other bacterial immunogens may also be released in the digestive tract following feeding dairy cows diets containing high proportions of grain. LPS can be translocated into the bloodstream across the epithelium of the digestive tract, especially the lower tract, due to possible alterations of permeability and injuries of the epithelial tissue. As a result, the concentration of blood LPS increases. Immune responses are subsequently caused by circulating LPS, and the systemic effects include increases in concentrations of neutrophils and the acute phase proteins such as serum amyloid-A (SAA), haptoglobin (Hp), LPS binding protein (LBP), and C-reactive protein (CRP) in blood. Entry of LPS into blood can also result in metabolic alterations. Blood glucose and nonesterified fatty acid concentrations are enhanced accompanying an increase of blood LPS after increasing the amount of grain in the diet, which adversely affects feed intake of dairy cows. As the proportions of grain in the diet increase, patterns of plasma β-hydoxybutyric acid, cholesterol, and minerals (Ca, Fe, and Zn) are also perturbed. The bacterial immunogens can also lead to reduced supply of nutrients for synthesis of milk components and depressed functions of the epithelial cells in the mammary gland. The immune responses and metabolic alterations caused by circulating bacterial immunogens will exert an effect on milk production. It has been demonstrated that increases in concentrations of ruminal LPS and plasma acute phase proteins (CRP, SAA, and LBP) are associated with declines in milk fat content, milk fat yield, 3.5% fat-corrected milk yield, as well as milk energy efficiency.

Population structure of rumen Escherichia coli associated with subacute ruminal acidosis (SARA) in dairy cattle

Previous studies indicated that only subacute ruminal acidosis (SARA), induced by feeding a high-grain diet, is associated with an inflammatory response and increased abundance of Escherichia coli in the rumen. We hypothesized that ruminal E. coli in grain pellet-induced SARA carried virulence factors that potentially contribute to the immune activation during SARA. One hundred twenty-nine E. coli isolates were cultured from the rumens of 8 cows (4 animals per treatment) in which SARA had been nutritionally induced by feeding a high-grain diet (GPI-SARA) or a diet containing alfalfa pellets (API-SARA). The population structure of the E. coli was evaluated with the ABD genotyping system and repetitive sequence-based (rep)-PCR fingerprinting. Twenty-five virulence factors were evaluated with PCR. Escherichia coli numbers were higher in the GPI-SARA treatment than in the API-SARA treatment. The genetic structure of the E. coli was significantly different between SARA challenge models. Isolates from GPI-control (46%), API-control (70%), and API-SARA (53%) were closely related and fell into one cluster, whereas isolates from GPI-SARA (54%) grouped separately. The ABD typing indicated a shift from an A-type E. coli population to a B1-type population only due to GPI-SARA. Of the 25 virulence factors tested, curli fiber genes were highly associated with GPI. Curli fibers were first identified in E. coli mastitis isolates and are potent virulence factors that induce a range of immune responses. Results suggest that under low rumen pH conditions induced by a grain diet, there is a burst in the number of E. coli with virulence genes that can take advantage of these rumen conditions to trigger an inflammatory response.

Factors influencing the persistence ofEscherichia coliO157:H7 lineages in feces from cattle fed grain versus grass hay diets

Escherichia coli O157:H7 is a pathogenic, gram-negative bacterium that causes diarrhea, hemorrhagic colitis, and can lead to fatal hemolytic uremic syndrome in humans. We examined the persistence of E. coli O157:H7 lineages I and II in feces held at 4, 12, and 25 °C, from animals fed either grain or hay diets. Three strains of each lineage I and II were inoculated into grain-fed or hay-fed feces, and their persistence was monitored over 28 days. No significant differences in E. coli O157:H7 survival between the 2 lineages in both fecal types was found at the examined temperatures. Volatile fatty acids were higher in grain-fed than in hay-fed feces, resulting in consistently lower pH in the grain-fed feces at 4, 12 and 25 °C. Regardless of lineage type, E. coli O157:H7 CFUs were significantly higher in grain-fed than in hay-fed feces at 4 and 25 °C. Escherichia coli O157:H7 survival was highest in grain-fed feces at 25 °C up to 14 days. Our results indicate that the 2 lineages of E. coli O157:H7 do not differ in their persistence; however, it appears that temperature and feces type both affect the survival of the pathogen.

Vaccination with attenuated Salmonella enterica Dublin expressing E coli O157:H7 outer membrane protein Intimin induces transient reduction of fecal shedding of E coli O157:H7 in cattle

Background

Escherichia coli serogroup O157:H7 has emerged as an important zoonotic bacterial pathogen, causing a range of symptoms from self-limiting bloody diarrhea to severe hemorrhagic colitis and hemolytic-uremic syndrome in humans. Beef and dairy cattle are considered the most important animal reservoirs for this pathogen. One of the important virulence characteristics of E. coli O157:H7 is the eaeA gene encoding the 97 kDa surface protein intimin. Intimin is required for attachment and effacement during the interaction of enterohemorrhagic E. coli with human and bovine neonatal enterocytes. The present study was undertaken to test the hypothesis that an adaptive mucosal immune response directed against intimin will reduce or prevent enteric colonization and fecal shedding of E. coli O157:H7 in cattle.

Results

Cattle were orally inoculated with either milk (control), milk with live attenuated Salmonella enterica serovar Dublin (vector), or milk with live attenuated recombinant S. Dublin expressing intimin (vaccinated) on days 0, 14 and 28. On day 98, all calves were challenged orally with E. coli O157:H7 to evaluate whether vaccination with the recombinant S. Dublin expressing intimin would reduce the level of E. coli O157:H7 fecal shedding.

During the first 28 days, vaccinated calves shed both the vector strain and the intimin-expressing S. Dublin strain at a similar level. The vector strain was shed for a significantly longer period as compared to the level of recombinant vaccine strain. Calves that received the intimin-expressed vaccine ceased shedding S. Dublin from day 28 to day 63. All calves were challenged with E. coli O157:H7 on day 98 to determine the effect on fecal shedding of E. coli O157:H7. The amount of E. coli O157:H7 in feces was measured for 30 days post-challenge. We observed a transient clearance of E. coli O157:H7 from the feces in the vaccinated calves. The magnitude of fecal E. coli O157:H7 shedding did not correlate with the presence of intimin-specific fecal IgA.

Conclusion

Oral vaccination with live attenuated recombinant S. Dublin expressing intimin reduced enteric colonization and fecal shedding of E. coli O157:H7. However, the transient clearance of E. coli O157:H7 was not associated with an enhanced IgA-mediated mucosal immune response.

Distribution and diversity of Escherichia coli populations in the South Nation River drainage basin, eastern Ontario, Canada

We investigated the prevalence and diversity of Escherichia coli strains isolated from surface waters from multiple watersheds within the South Nation River basin in eastern Ontario, Canada. The basin is composed of mixed but primarily agricultural land uses. From March 2004 to November 2007, a total of 2,004 surface water samples were collected from 24 sampling sites. E. coli densities ranged from undetectable to 1.64 x 10(5) CFU 100 ml(-1) and were correlated with stream order and proximity to livestock production systems. The diversity of 21,307 E. coli isolates was characterized using repetitive extragenic palindromic PCR (rep-PCR), allowing for the identification of as many as 7,325 distinct genotypes, without capturing all of the diversity. The community was temporally and spatially dominated by a few dominant genotypes (clusters of more than 500 isolates) and several genotypes of intermediary abundance (clustering between 10 and 499 isolates). Simpson diversity indices, assessed on a normalized number of isolates per sample, ranged from 0.050 to 0.668. Simpson indices could be statistically discriminated on the basis of year and stream order, but land use, discharge, weather, and water physical-chemical properties were not statistically important discriminators. The detection of Campylobacter species was associated with statistically lower Simpson indices (greater diversity; P < 0.05). Waterborne E. coli isolates from genotypes of dominant and intermediary abundance were clustered with isolates obtained from fecal samples collected in the study area over the same period, and 90% of the isolates tested proved to share genotypes with fecal isolates. Overall, our data indicated that the densities and distribution of E. coli in these mixed-use watersheds were linked to stream order and livestock-based land uses. Waterborne E. coli populations that were distinct from fecal isolates were detected and, on this basis, were possibly naturalized E. coli strains.

Optimization and validation of rep-PCR genotypic libraries for microbial source tracking of environmental Escherichia coli isolates

Escherichia coli can be used to help identify sources of fecal contamination in the environment. Escherichia coli genotypic fecal libraries and pattern-matching algorithms were assessed for their effectiveness in correctly identifying sources. Fecal samples (n = 172) were collected from various sources from three agricultural landscapes in Canada. Escherichia coli isolates were fingerprinted using BOX- and enterobacterial repetitive intergenic consensus (ERIC) - polymerase chain reaction primers, revealing 769 and 1 057 distinct genotypes, respectively, for the 9 047 isolates collected in 2004 in Ontario. The average rate of correct classification (ARCC) was comparable for BOX- (48%) and ERIC-based (62%) libraries and between libraries with clones removed per sample (55%) and clones removed per unit (54%). ARCC increased with fewer classification units (from 44% to 65%). ARCC for k-nearest neighbour (64%) and maximum similarity (60%) algorithms were comparable, but maximum similarity had better sensitivity and specificity than k-nearest neighbour. Geographical and temporal shifts in community composition resulted in loss of accuracy. Several ERIC genotypes (n = 112) were common between sources and were removed from the library, improving ARCC (77%). The latter library proved to be more accurate, but its accuracy with respect to sourcing environmental isolates remains to be tested.

Dietary interactions and interventions affecting Escherichia coli O157 colonization and shedding in cattle

Escherichia coli O157 is an important foodborne pathogen affecting human health and the beef cattle industry. Contamination of carcasses at slaughter is correlated to the prevalence of E. coli O157 in cattle feces. Many associations have been made between dietary factors and E. coli O157 prevalence in cattle feces. Preharvest interventions, such as diet management, could reduce the fecal prevalence and diminish the impact of this adulterant. Dietary influences, including grain type and processing method, forage quality, and distillers grains have all been associated with E. coli O157 prevalence. In addition, several plant compounds, including phenolic acids and essential oils, have been proposed as in-feed intervention strategies. The specific mechanisms responsible for increased or decreased E. coli O157 shedding or survival are not known but are often attributed to changes in hindgut ecology induced by diet types. Some interventions may have a direct bacterial effect. Frequently, results of studies are conflicting or not repeatable, which speaks to the complexity of the hindgut ecosystem, variation in animal feed utilization, and variation within feed products. Still, understanding specific mechanisms, driven by diet influences, responsible for E. coli O157 shedding will aid in the development and implementation of better and practical preharvest intervention strategies.

Characterization of tetracycline- and ampicillin-resistant Escherichia coli isolated from the feces of feedlot cattle over the feeding period

The objective of this study was to investigate tetracycline and ampicillin resistance in Escherichia coli isolated from the feces of 50 crossbred steers housed in 5 feedlot pens. The steers were not administered antibiotics over a 246-day feeding period. A total of 216 isolates were selected for further characterization. The E. coli isolates were selected on MacConkey agar or on MacConkey agar amended with ampicillin (50 microg/mL) or tetracycline (4 microg/mL). Pulsed-field gel electrophoresis (PFGE) typing (XbaI digestion), screening against 11 antibiotics, and multiplex PCR for 14 tet and 3 beta-lactamase genes were conducted. Prevalence of antimicrobial resistance in E. coli at each sampling day was related both temporally and by pen. Multiplex PCR revealed that tet(B) was most prevalent among tetracycline-resistant isolates, whereas beta-lactamase tem1-like was detected mainly in ampicillin-resistant isolates. Our results suggest that antimicrobial resistance in E. coli populations persists over the duration of the feeding period, even in the absence of in-feed antibiotics. Many of the isolates with the same antibiograms had indistinguishable PFGE patterns. Characterization of the factors that influence the nature of this nonselective resistance could provide important information for consideration in the regulation of in-feed antimicrobials for feedlot cattle.

Remodeling and activation of Escherichia coli RNA polymerase by osmolytes

The ability of bacteria to survive environmental stresses and colonize the gastrointestinal tract depends on adaptation to high osmolarity. The adaptation involves global reprogramming of gene expression, including inhibition of bulk sigma70 RNA polymerase transcription and activation of bulk sigma38 transcription. The activating signal transduction pathways that originate with osmolytes remain to be established. Experiments here confirm that accumulation of a simple signaling molecule, glutamate, can reprogram RNA polymerase in vitro without the need for specific protein receptors. During osmotic activation, glutamate appears to act as a Hofmeister series osmolyte to facilitate promoter escape. Escape is accompanied by a remodeling of the key interaction between the sigma38 stress protein and the beta-flap of the bacterial core RNA polymerase. This activation event contrasts with the established mechanism of inhibition in which glutamate, by virtue of its electrostatic properties, helps to inhibit binding to ribosomal promoters after osmotic shock. Overall, Escherichia coli survival in natural hosts and reservoirs is expected to rely on the accumulation of simple ions that trigger changes in protein conformation that lead to global changes in transcription.

Escherichia coli populations in Great Lakes waterfowl exhibit spatial stability and temporal shifting

Populations of Escherichia coli from juvenile and adult ring-billed gulls, juvenile common terns, and adult Canada geese were sampled over 6 years at five locations on Lake Superior (Duluth, MN, and Wisconsin) and Lake Michigan (Wisconsin, Illinois, and Indiana) to determine the extent of spatial and temporal variability in E. coli strains. Strain identity was determined using horizontal fluorophore-enhanced repetitive element palindromic DNA fingerprinting. Multivariate statistics were used to determine if spatial or temporal changes in E. coli populations occurred in waterfowl species. Pairwise multivariate analyses of variance revealed that E. coli populations of adult gulls from three regions of Lake Michigan and the Wisconsin shore of Lake Superior were similar to one another but different from an E. coli population of gulls from the Duluth region of Lake Superior. Juvenile and adult gulls from the Duluth area harbored different E. coli populations. The E. coli strains from juvenile gulls, however, were similar to those found in juvenile terns obtained from the same island rookery. Temporal changes in E. coli populations from several waterfowl species were also demonstrated for this site. Although portions of source tracking databases might be successfully used in other geographic regions, it is clear that juvenile birds should not be the sole source of E. coli strains used for source tracking databases, and multiple-year libraries should be constructed in order to identify the potential sources of E. coli in the environment.

Reuse of concentrated animal feeding operation wastewater on agricultural lands

Concentrated animal feeding operations (CAFOs) generate large volumes of manure and manure-contaminated wash and runoff water. When applied to land at agronomic rates, CAFO wastewater has the potential to be a valuable fertilizer and soil amendment that can improve the physical condition of the soil for plant growth and reduce the demand for high quality water resources. However, excess amounts of nutrients, heavy metals, salts, pathogenic microorganisms, and pharmaceutically active compounds (antibiotics and hormones) in CAFO wastewater can adversely impact soil and water quality. The USEPA currently requires that application of CAFO wastes to agricultural lands follow an approved nutrient management plan (NMP). A NMP is a design document that sets rates for waste application to meet the water and nutrient requirements of the selected crops and soil types, and is typically written so as to be protective of surface water resources. The tacit assumption is that a well-designed and executed NMP ensures that all lagoon water contaminants are taken up or degraded in the root zone, so that ground water is inherently protected. The validity of this assumption for all lagoon water contaminants has not yet been thoroughly studied. This review paper discusses our current level of understanding on the environmental impact and sustainability of CAFO wastewater reuse. Specifically, we address the source, composition, application practices, environmental issues, transport pathways, and potential treatments that are associated with the reuse of CAFO wastewater on agricultural lands.

Development of a risk-based index for source water protection planning, which supports the reduction of pathogens from agricultural activity entering water resources

Source water protection planning (SWPP) is an approach to prevent contamination of ground and surface water in watersheds where these resources may be abstracted for drinking or used for recreation. For SWPP the hazards within a watershed that could contribute to water contamination are identified together with the pathways that link them to the water resource. In rural areas, farms are significant potential sources of pathogens. A risk-based index can be used to support the assessment of the potential for contamination following guidelines on safety and operational efficacy of processes and practices developed as beneficial approaches to agricultural land management. Evaluation of the health risk for a target population requires knowledge of the strength of the hazard with respect to the pathogen load (massxconcentration). Manure handling and on-site wastewater treatment systems form the most important hazards, and both can comprise confined and unconfined source elements. There is also a need to understand the modification of pathogen numbers (attenuation) together with characteristics of the established pathways (surface or subsurface), which allow the movement of the contaminant species from a source to a receptor (water source). Many practices for manure management have not been fully evaluated for their impact on pathogen survival and transport in the environment. A key component is the identification of potential pathways of contaminant transport. This requires the development of a suitable digital elevation model of the watershed for surface movement and information on local groundwater aquifer systems for subsurface flows. Both require detailed soils and geological information. The pathways to surface and groundwater resources can then be identified. Details of land management, farm management practices (including animal and manure management) and agronomic practices have to be obtained, possibly from questionnaires completed by each producer within the watershed. To confirm that potential pathways are active requires some microbial source tracking. One possibility is to identify the molecular types of Escherichia coli present in each hazard on a farm. An essential part of any such index is the identification of mitigation strategies and practices that can reduce the magnitude of the hazard or block open pathways.

Effect of subtherapeutic administration of antibiotics on the prevalence of antibiotic-resistant Escherichia coli bacteria in feedlot cattle

Antibiotic-resistant Escherichia coli in 300 feedlot steers receiving subtherapeutic levels of antibiotics was investigated through the collection of 3,300 fecal samples over a 314-day period. Antibiotics were selected based on the commonality of use in the industry and included chlortetracycline plus sulfamethazine (TET-SUL), chlortetracycline (TET), virginiamycin, monensin, tylosin, or no antibiotic supplementation (control). Steers were initially fed a barley silage-based diet, followed by transition to a barley grain-based diet. Despite not being administered antibiotics prior to arrival at the feedlot, the prevalences of steers shedding TET- and ampicillin (AMP)-resistant E. coli were >40 and <30%, respectively. Inclusion of TET-SUL in the diet increased the prevalence of steers shedding TET- and AMP-resistant E. coli and the percentage of TET- and AMP-resistant E. coli in the total generic E. coli population. Irrespective of treatment, the prevalence of steers shedding TET-resistant E. coli was higher in animals fed grain-based compared to silage-based diets. All steers shed TET-resistant E. coli at least once during the experiment. A total of 7,184 isolates were analyzed for MIC of antibiotics. Across antibiotic treatments, 1,009 (13.9%), 7 (0.1%), and 3,413 (47.1%) E. coli isolates were resistant to AMP, gentamicin, or TET, respectively. In addition, 131 (1.8%) and 143 (2.0%) isolates exhibited potential resistance to extended-spectrum beta-lactamases, as indicated by either ceftazidime or cefpodoxime resistance. No isolates were resistant to ciprofloxacin. The findings of the present study indicated that subtherapeutic administration of tetracycline in combination with sulfamethazine increased the prevalence of tetracycline- and AMP-resistant E. coli in cattle. However, resistance to antibiotics may be related to additional environmental factors such as diet.

Effects of dried distillers' grain on fecal prevalence and growth of Escherichia coli O157 in batch culture fermentations from cattle

Distillers' grains (DG), a by-product of ethanol production, are fed to cattle. Associations between Escherichia coli O157 prevalence and feeding of DG were investigated in feedlot cattle (n = 379) given one of three diets: steam-flaked corn (SFC) and 15% corn silage with 0 or 25% dried distillers' grains (DDG) or SFC with 5% corn silage and 25% DDG. Ten fecal samples were collected from each pen weekly for 12 weeks to isolate E. coli O157. Cattle fed 25% DDG with 5 or 15% silage had a higher (P = 0.01) prevalence of E. coli O157 than cattle fed a diet without DDG. Batch culture ruminal or fecal microbial fermentations were conducted to evaluate the effect of DDG on E. coli O157 growth. The first study utilized microbial inocula from steers fed SFC or dry-rolled corn with 0 or 25% DDG and included their diet as the substrate. Ruminal microbial fermentations from steers fed DDG had higher E. coli O157 contents than ruminal microbial fermentations from steers fed no DDG (P < 0.05) when no substrate was included. Fecal fermentations showed no DDG effect on E. coli O157 growth. In the second study with DDG as a substrate, ruminal fermentations with 0.5 g DDG had higher (P < 0.01) E. coli O157 concentrations at 24 h than ruminal fermentations with 0, 1, or 2 g DDG. In fecal fermentations, 2 g DDG resulted in a higher concentration (P < 0.05) at 24 h than 0, 0.5, or 1 g DDG. The results indicate that there is a positive association between DDG and E. coli O157 in cattle, and the findings should have important ramifications for food safety.

Grazing protozoa and the evolution of the Escherichia coli O157:H7 Shiga toxin-encoding prophage

Humans play little role in the epidemiology of Escherichia coli O157:H7, a commensal bacterium of cattle. Why then does E. coli O157:H7 code for virulence determinants, like the Shiga toxins (Stxs), responsible for the morbidity and mortality of colonized humans? One possibility is that the virulence of these bacteria to humans is coincidental and these virulence factors evolved for and are maintained for other roles they play in the ecology of these bacteria. Here, we test the hypothesis that the carriage of the Stx-encoding prophage of E. coli O157:H7 increases the rate of survival of E. coli in the presence of grazing protozoa, Tetrahymena pyriformis. In the presence but not the absence of Tetrahymena, the carriage of the Stx-encoding prophage considerably augments the fitness of E. coli K-12 as well as clinical isolates of E. coli O157 by increasing the rate of survival of the bacteria in the food vacuoles of these ciliates. Grazing protozoa in the environment or natural host are likely to play a significant role in the ecology and maintenance of the Stx-encoding prophage of E. coli O157:H7 and may well contribute to the evolution of the virulence of these bacteria to colonize humans.

Temporal dynamics and impact of manure storage on antibiotic resistance patterns and population structure of Escherichia coli isolates from a commercial swine farm

Many confined-livestock farms store their wastes for several months prior to use as a fertilizer. Storing manure for extended periods could significantly bias the composition of enteric bacterial populations subsequently released into the environment. Here, we compared populations of Escherichia coli isolated from fresh feces and from the manure-holding tank (stored manure) of a commercial swine farm, each sampled monthly for 6 months. The 4,668 confirmed E. coli isolates were evaluated for resistance to amikacin, ampicillin, cephalothin, chloramphenicol, kanamycin, nalidixic acid, streptomycin, sulfamethoxazole, tetracycline, trimethoprim, and trimethoprim plus sulfamethoxazole. A subset of 1,687 isolates was fingerprinted by repetitive extragenic palindromic PCR (rep-PCR) with the BOXA1R primer to evaluate the diversity and the population structure of the collection. The population in the stored manure was generally more diverse than that in the fresh feces. Half of the genotypes detected in the stored manure were never detected in the fresh fecal material, and only 16% were detected only in the fresh feces. But the majority of the isolates (84%) were assigned to the 34% of genotypes shared between the two environments. The structure of the E. coli population showed important monthly variations both in the extent and distribution of the diversity of the observed genotypes. The frequency of detection of resistance to specific antibiotics was not significantly different between the two collections and varied importantly between monthly samples. Resistance to multiple antibiotics was much more temporally dynamic in the fresh feces than in the stored manure. There was no relationship between the distribution of rep-PCR fingerprints and the distribution of antibiotic resistance profiles, suggesting that specific antibiotic resistance determinants were dynamically distributed within the population.

Characterization of enterococci populations in livestock manure using BIOLOG

The BIOLOG system was used to generate knowledge of enterococci populations found in fresh and dry manure of livestock (cattle (Bos taurus), horse (Equus caballus), and sheep (Ovis aires)). Six-hundred and forty Enterococcus isolates from the host sources were observed as a combined fresh manure unit and a combined dry manure unit, E. casseliflavus and E. mundtii were predominant in fresh manure (36% and 35%, respectively) as well as in dry manure (51% and 28%, respectively). The other species were found at a frequency of less than 10%. A chi-square test of the two most predominant Enterococcus sp. indicated that there were some significant differences among the frequency of E. casseliflavus and E. mundtii in cattle and sheep, but not horse. Despite these differences, these two species were overwhelmingly predominant among all three livestock sources.

EnterohemorrhagicEscherichia coliO157: epidemiology and ecology in bovine production environments

EnterohemorrhagicEscherichia coli, particularly the O157(:H7) serogroup, has become a worldwide public health concern. Since cattle feces are often implicated as the source ofE. coliO157 in human infections, considerable resources have been devoted to defining the epidemiology and ecology ofE. coliO157 in cattle environments so that control might begin at the farm level. Diagnostic limitations and the complexity of often interrelated microbial, animal, herd, environmental and production factors have hindered the determination of the epidemiology, ecology and subsequent farm-level control ofE. coliO157. The widespread distribution ofE. coliO157, the transitory nature of fecal shedding, multiple potential environmental sources, lack of species specificity, and age-, feed- and time-related differences in cattle prevalence are documented. However, the significance and/or role of these factors in the epidemiology and ecology ofE. coliO157 is still unclear. Cattle are a major source ofE. coliO157, but it may be simplistic to believe that most herds are relatively closed systems with small percentages of cattle serving as true reservoirs. Practical on-farm control may require explicit definitions of the seemingly complex system(s) and the microbial, animal, herd, environmental and production factors involved in the multiplication, maintenance and transmission ofE. coliO157.

Methodological Quality Assessment of Review Articles Evaluating Interventions to Improve Microbial Food Safety

Review articles are a means of summarizing the potentially vast volume of research on a topic. However, the methodological quality of review articles varies, and reviews on the same topic may reach different conclusions. We evaluated 65 review articles published between 2000 and 2005 that addressed the effectiveness of microbial food safety interventions, using criteria for methodological soundness developed in the medical field. Overall, the methodological quality of the review articles was poor, with none of the reviews providing information on the method of locating primary research studies or the inclusion/exclusion criteria for selecting primary studies. None of the reviews included a critical appraisal of the methodological quality of the primary studies. Less than half of the reviews stated a focused research question, explored possible reasons for differences in the results of primary studies, discussed the generalizability of results, or proposed directions for future research. There is a need to improve the methodological quality of review articles on microbial food safety interventions if they are to be of use in policy and decision making.

Shiga toxin-producing Escherichia coli: an overview

The objective of this review is to highlight the importance of cattle in human disease due to Shiga toxin-producing Escherichia coli (STEC) and to discuss features of STEC that are important in human disease. Healthy dairy and beef cattle are a major reservoir of a diverse group of STEC that infects humans through contamination of food and water, as well as through direct contact. Infection of humans by STEC may result in combinations of watery diarrhea, bloody diarrhea, and hemolytic uremic syndrome. Systems of serotyping, subtyping, and virulence typing of STEC are used to aid in epidemiology, diagnosis, and pathogenesis studies. Severe disease and outbreaks of disease are most commonly due to serotype O157:H7, which, like most other highly pathogenic STEC, colonize the large intestine by means of a characteristic attaching and effacing lesion. This lesion is induced by a bacterial type III secretion system that injects effector proteins into the intestinal epithelial cell, resulting in profound changes in the architecture and metabolism of the host cell and intimate adherence of the bacteria. Severe disease in the form of bloody diarrhea and the hemolytic uremic syndrome is attributable to Shiga toxin (Stx), which exists as 2 major types, Stx1 and Stx2. The stx genes are encoded on temperate bacteriophages in the chromosome of the bacteria, and production and release of the toxin are highly dependent on induction of the phages. Regulation of the genes involved in induction of the attaching and effacing lesion, and production of Stx is complex. In addition to these genes that are clearly implicated in virulence, there are several putative virulence factors. A major public health goal is to prevent STEC-induced disease in humans. Studies aimed at understanding factors that affect carriage and shedding of STEC by cattle and factors that contribute to development of disease in humans are considered to be important in achieving this objective.

A semi-stochastic model of the transmission of Escherichia coli O157 in a typical UK dairy herd: dynamics, sensitivity analysis and intervention/prevention strategies

When modelling the transmission of infection within small populations, it is necessary to consider the possibility of stochastic fade-out of infection. We present a semi-stochastic model for the transmission of a microparasite, in this case Escherichia coli O157, within a multigroup system, namely a typical UK dairy herd. The model includes birth, death, maturation, the dry/lactating cycle and various types of transmission (i.e. direct, pseudovertical (representing direct faecal-oral transmission between dam and calf within the first 48 h) and indirect (via free-living infectious units in the environment)). We present the results of our simulation study alongside data from empirical studies and also compare simulation results with those for the corresponding deterministic model. We then examine the effects of reducing shedding in the food-producing groups on outbreak size and prevalence of infection. A sensitivity analysis of herd prevalence reveals that, for both the deterministic and the semi-stochastic model, the prevalence within the herd is most sensitive to two parameters relating to the weaned group. This supports our previously reported conclusions for the deterministic model, which were based on an analysis of the next-generation matrix. The sensitivity analysis also indicates that herd prevalence is greatly affected by two other parameters relating to the lactating group. We conclude by discussing the possible efficacy of suggested intervention strategies.

Identifying host sources of fecal pollution: diversity of Escherichia coli in confined dairy and swine production systems

Repetitive extragenic palindromic PCR fingerprinting of Escherichia coli is one microbial source tracking approach for identifying the host source origin of fecal pollution in aquatic systems. The construction of robust known-source libraries is expensive and requires an informed sampling strategy. In many types of farming systems, waste is stored for several months before being released into the environment. In this study we analyzed, by means of repetitive extragenic palindromic PCR using the enterobacterial repetitive intergenic consensus primers and comparative analysis using the Bionumerics software, collections of E. coli obtained from a dairy farm and from a swine farm, both of which stored their waste as a slurry in holding tanks. In all fecal samples, obtained from either barns or holding tanks, the diversity of the E. coli populations was underrepresented by collections of 500 isolates. In both the dairy and the swine farms, the diversity of the E. coli community was greater in the manure holding tank than in the barn, when they were sampled on the same date. In both farms, a comparison of stored manure samples collected several months apart suggested that the community composition changed substantially in terms of the detected number, absolute identity, and relative abundance of genotypes. Comparison of E. coli populations obtained from 10 different locations in either holding tank suggested that spatial variability in the E. coli community should be accounted for when sampling. Overall, the diversity in E. coli populations in manure slurry storage facilities is significant and likely is problematic with respect to library construction for microbial source tracking applications.

Influence of flavomycin on microbial numbers, microbial metabolism and gut tissue protein turnover in the digestive tract of sheep

Flavomycin is an antibiotic that promotes growth in ruminant and non-ruminant livestock. The aim of this study was to determine the mechanism of action of flavomycin in sheep by measuring microbial numbers, microbial metabolism and gut tissue protein turnover at different sites in the digestive tract. Two weight-matched groups (n 5) of male castrate lambs (30 kg) received 800 g grass cubes/d for 6 weeks, with one group receiving 20 mg/d flavomycin during the last 2 weeks. Samples of digesta and gut tissue segments were obtained immediately post mortem, 90 min after a flood-dose of [ring-D5]phenylalanine. Viable bacterial counts and volatile fatty acid concentrations were highest in ruminal digesta, followed by the colon and caecum, then the duodenum and ileum. The only effect of flavomycin was an increased bacterial count in the rumen (3.5 v. 1.2 x 10(9) per g; P=0.04). Acetate was proportionally greater and propionate and butyrate were lower in the caecum and colon than the rumen. Flavomycin had no effect on volatile fatty acid proportions or ammonia concentrations. Bacteria growing on peptides as sole C source were not affected by flavomycin. Proteolytic, peptidolytic and amino acid deamination activities were similar in the rumen, caecum and colon; they tended to be lower in animals receiving flavomycin. Protein turnover in ruminal wall and duodenal tissues, measured by a flood-dose technique, decreased with flavomycin (P=0.075 and 0.027, respectively). Thus, flavomycin differs from ionophores in its mode of action. It may influence protein metabolism of both digesta and tissue throughout the ruminant digestive tract.

Effect of finishing diets on Escherichia coli populations and prevalence of enterohaemorrhagic E. coli virulence genes in cattle faeces

AIM

To determine the effect of different carbohydrate-based finishing diets on fermentation characteristics and the shedding of Escherichia coli and enterohaemorrhagic E. coli (EHEC) virulence genes in cattle faeces.

METHODS AND RESULTS

The size of faecal E. coli populations and fermentation characteristics were ascertained in three experiments where cattle were maintained on a range of finishing diets including high grain, roughage, and roughage + molasses (50%) diets. Increased E. coli numbers, decreased pH and enhanced butyrate and lactate fermentation pathways were associated with grain diets, whereas roughage and roughage + molasses diets resulted in decreased concentrations of ehxA, eaeA and stx(1) genes, this trend remaining at lairage. In one experiment, faecal E. coli numbers were significantly lower in animals fed roughage and roughage + molasses, than animals fed grain (4.5, 5.2 and 6.3 mean log10 g(-1) digesta respectively). In a second experiment, faecal E. coli numbers were 2 log lower in the roughage and roughage + molasses diets compared with grain-fed animals prior to lairage (5.6, 5.5 and 7.9 mean log10 g(-1) digesta respectively) this difference increasing to 2.5 log at lairage.

CONCLUSIONS

The type of dietary carbohydrate has a significant effect on E. coli numbers and concentration of EHEC virulence genes in faeces of cattle.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides a better understanding of the impact finishing diet and commercial lairage management practices may have on the shedding of E. coli and EHEC virulence factors, thus reducing the risk of carcass contamination by EHEC.

Numbers of fecal streptococci and Escherichia coli in fresh and dry cattle, horse, and sheep manure

Livestock are known contributors to stream pollution. Numbers of fecal streptococci and Escherichia coli in manure naturally deposited by livestock in the field are needed for activities related to bacterial source tracking and determining maximum daily bacterial loading of streams. We measured populations of fecal streptococci and E. coli in fresh and dry manure from cattle (Bos taurus L.), horses (Equus caballus L.), and sheep (Ovis aires L.) on farms in southern Idaho. Populations of indicator bacteria in dry manure were often as high as that in fresh manure from horse and sheep. There was a 2 log10 drop in the population of fecal coliform numbers in dry cattle manure from cattle in pastures but not from cattle in pens. Bacterial isolates used in source tracking should include isolates from both fresh and dry manure to better represent the bacterial source loading of streams.Key words: enterococci, E. coli, fecal streptococci, bacterial indicators, bacterial source tracking, pollution.

A lack of predatory interaction between rumen ciliate protozoa and Shiga-toxin producing Escherichia coli

AIMS

To investigate interactions between rumen protozoa and Shiga toxin-producing Escherichia coli (STEC) and to ascertain whether it is likely that rumen protozoa act as ruminant hosts for STEC.

METHODS AND RESULTS

The presence of stx genes in different microbial fractions recovered from cattle and sheep rumen contents and faeces was examined using PCR. In animals shedding faecal STEC, stx genes were not detected in the rumen bacterial or rumen protozoal fractions. Direct interactions between ruminal protozoa and STEC were investigated by in vitro co-incubation. Rumen protozoa did not appear to ingest STEC, a STEC lysogen or non-STEC E. coli populations when co-incubated.

CONCLUSIONS

The ruminal environment is unlikely to be a preferred habitat for STEC. Bacterial grazing by rumen protozoa appears to have little, if any, effect on STEC populations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicates that ruminal protozoa are unlikely to be a major factor in the survival of STEC in ruminants. They appear as neither a host that protects STEC from the ruminal environment nor a predator that might reduce STEC numbers.

Effect of forage or grain diets with or without monensin on ruminal persistence and fecal Escherichia coli O157:H7 in cattle

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:H7. Cattle were ruminally inoculated with a strain of E. coli O157:H7 (10(10) CFU/animal) made resistant to nalidixic acid (Nal(r)). Ruminal and fecal samples were collected for 11 weeks, and then cattle were euthanized and necropsied and digesta from different gut locations were collected. Samples were cultured for detection and enumeration of Nal(r) E. coli O157:H7. Cattle fed forage diets were culture positive for E. coli O157:H7 in the feces for longer duration (P < 0.05) than cattle fed a grain diet. In forage-fed cattle, the duration they remained culture positive for E. coli O157:H7 was shorter (P < 0.05) when the diet included monensin. Generally, ruminal persistence of Nal(r) E. coli O157:H7 was not affected by diet or monensin. At necropsy, E. coli O157:H7 was detected in cecal and colonic digesta but not from the rumen. Our study showed that cattle fed a forage diet were culture positive longer and with higher numbers than cattle on a grain diet. Monensin supplementation decreased the duration of shedding with forage diet, and the cecum and colon were culture positive for E. coli O157:H7 more often than the rumen of cattle.

Escherichia coli O157:H7 in a cohort of weaned, preconditioned range beef calves

Escherichia coli O157:H7 (EC O157) is an important cause of foodborne disease. Cattle are reservoirs for the bacteria and are implicated in transmission to humans. Prevalence data in prefeedlot calves are limited. With the use of sensitive methods, a cohort of weaned beef calves (n = 408) was sampled before and after preconditioning to estimate fecal point prevalence and describe changes in EC O157 fecal shedding. EC O157 isolates were confirmed and characterized by PCR and pulsed-field gel electrophoresis. Calves from 29 cow-calf farms were commingled at three preconditioning sites and placed on a transition ration containing oxytetracycline (200 g/ton) for 45 days. Initial animal-level fecal point prevalence was 2.5% (95% confidence interval, 1 to 5) with a herd-level prevalence of 17.2% (95% confidence interval, 6 to 36). Point prevalence following the preconditioning feeding period was 0%. An unexpected finding in our study was EC O157 isolates that were Shiga toxin-deficient. Pulsed-field gel electrophoresis subtypes of EC O157 were unique in epidemiologically unlinked herds, except one herd that had two unique subtypes. We expected, but observed, neither increased fecal shedding in the cohort nor horizontal transmission of unique EC O157 subtypes. The absence of fecal shedding following the 45-day feeding period might be attributable to seasonal influences, inhibitory concentrations of oxytetracycline in the transition ration, or transient colonization that ended before sampling. EC O157 is apparently widely dispersed at low prevalence in U.S. prefeedlot, weaned calves.

Escherichia coli contamination of vegetables grown in soils fertilized with noncomposted bovine manure: garden-scale studies

In this study we tested the validity of the National Organic Program (NOP) requirement for a > or =120-day interval between application of noncomposted manure and harvesting of vegetables grown in manure-fertilized soil. Noncomposted bovine manure was applied to 9.3-m2 plots at three Wisconsin sites (loamy sand, silt loam, and silty clay loam) prior to spring and summer planting of carrots, radishes, and lettuce. Soil and washed (30 s under running tap water) vegetables were analyzed for indigenous Escherichia coli. Within 90 days, the level of E. coli in manure-fertilized soil generally decreased by about 3 log CFU/g from initial levels of 4.2 to 4.4 log CFU/g. Low levels of E. coli generally persisted in manure-fertilized soil for more than 100 days and were detected in enriched soil from all three sites 132 to 168 days after manure application. For carrots and lettuce, at least one enrichment-negative sample was obtained < or =100 days after manure application for 63 and 88% of the treatments, respectively. The current > or =120-day limit provided an even greater likelihood of not detecting E. coli on carrots (> or =1 enrichment-negative result for 100% of the treatments). The rapid maturation of radishes prevented conclusive evaluation of a 100- or 120-day application-to-harvest interval. The absolute absence of E. coli from vegetables harvested from manure-fertilized Wisconsin soils may not be ensured solely by adherence to the NOP > or =120-day limit. Unless pathogens are far better at colonizing vegetables than indigenous E. coli strains are, it appears that the risk of contamination for vegetables grown in Wisconsin soils would be elevated only slightly by reducing the NOP requirement to > or =100 days.

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.