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Foodborne pathogenic bacteria can live in the intestinal tract of food animals and can be transmitted to humans via food or indirectly through animal or fecal contact. Organic acid blend products have been used as nonantibiotic modifiers of the gastrointestinal fermentation of food animals to improve growth performance efficiency. However, the impact of these organic acid products on the microbial population, including foodborne pathogens, remains unknown. Therefore, this study was designed to examine the effects of a commercial organic acid and botanical blend product (OABP) on populations of the foodborne pathogenic bacteria, Escherichia coli O157:H7 and Salmonella Typhimurium. Pure cultures (2 · 10 6 colony-forming units [CFU]/mL) of each pathogen were added to tubes that contained water-solubilized OABP added at concentrations of 0, 0.1, 0.5, 1, 2, 5, and 10% (vol/vol; n = 3). Water-solubilized OABP reduced ( p < 0.05) the growth rate and final populations of E. coli O157:H7 and Salmonella Typhimurium in pure culture at concentrations > 2%. E. coli O157:H7 and Salmonella Typhimurium were added (2 · 10 5 and 3 · 10 6 CFU/mL, respectively) to in vitro mixed ruminal microorganism fermentations that contained water-solubilized OABP at concentrations of 0, 1, 2, 5, and 10% (vol/vol; n = 3) that were incubated for 24 h. OABP addition reduced ( p < 0.05) final populations of E. coli O157:H7 and Salmonella Typhimurium in the ruminal fluid at concentrations ‡ 5%. The acetate–to-propionate ratios from the in vitro fermentations were reduced ( p < 0.05) by OABP treatment ‡ 5%. Treatments to reduce foodborne pathogens must be economically feasible to implement, and results indicate that organic acid products, such as OABP, can enhance animal growth efficiency and can be used to reduce populations of pathogenic bacteria.

Salmonella is a foodborne pathogenic bacterium that causes human illnesses and morbidity and mortality in swine. Bacteriophages are viruses that prey on bacteria and are naturally found in many microbial environments, including the gut of food animals, and have been suggested as a potential intervention strategy to reduce Salmonella levels in the live animal. The present study was designed to determine if anti-Salmonella phages isolated from the feces of commercial finishing swine could reduce gastrointestinal populations of the foodborne pathogen Salmonella Typhimurium in artificially inoculated swine. Weaned pigs (n = 48) were randomly assigned to two treatment groups (control or phage-treated). Each pig was inoculated with Salmonella Typhimurium (2 × 10(10) colony forming units/pig) via oral gavage at 0 h and fecal samples were collected every 24 h. Swine were inoculated with a phage cocktail via oral gavage (3 × 10(9) plaque forming units) at 24 and 48 h. Pigs were humanely killed at 96 h, and cecal and rectal intestinal contents were collected for quantitative and qualitative analysis. Fecal Salmonella populations in phage-treated pigs were lower (p 0.09) than controls after 48 h. Phage treatment reduced intestinal populations of inoculated Salmonella Typhimurium in pigs compared to controls at necropsy. Cecal populations were reduced (p = 0.07) by phage treatment1.4 log(10) colony forming units/g digesta, and rectal populations were numerically reduced. The number of pigs that contained inoculated Salmonella Typhimurium was reduced by phage treatment, but a significant (p 0.05) reduction was only observed in the rectum. We conclude that phages can be a viable tool to reduce Salmonella in swine. Further research needs to be performed to determine the most efficacious dosing regimens and the most effective combinations of phages targeting the diverse Salmonella population found in swine before they can enter the food supply.

Campylobacter are important human foodborne pathogens known to colonize the gastrointestinal tract of cattle. The incidence of Campylobacter in cattle may be seasonal and may vary among age groups and type (beef versus dairy). Less is known about other factors that could influence the prevalence, colonization site, and shedding of Campylobacter in cattle. The objectives of this study were to evaluate the prevalence and enumerate Campylobacter at two sites along the digestive tract of beef and dairy type cattle consuming either grass or feedlot diets. In an initial study, Campylobacter was not recovered from rumen samples of any of 10 ruminally cannulated (six dairy and four beef type) pasture-reared cattle and there was no difference (p0.05) between cattle types on fecal Campylobacter recovery, with 50% of each type yielding culture-positive feces (overall mean +/- SE, 0.75 +/- 0.001 SEM log(10) colony-forming units [CFU]/g feces). When calculated from Campylobacter culture-positive animals only, mean fecal concentrations were 1.50 +/- 0.001 SEM log(10) CFU/g. In a follow-up study with feedlot and pasture-reared cattle (n = 18 head each), 78% of rumen and 94% of fecal samples from pastured cattle were positive for Campylobacter while 50% of the rumen and 72% of the fecal samples were positive in concentrate-fed animals. Overall mean concentration of Campylobacter was greater in feces than ruminal fluid (p0.05). When only Campylobacter-positive animals were analyzed, concentrations recovered from feces were higher (p0.05) in concentrate-fed than in pasture-fed cattle (4.29 vs. 3.34 log(10) CFU/g, respectively; SEM = 0.29). Our results suggest that the rumen environment and its microbial population are less favorable for the growth of Campylobacter and that concentrate diets may provide a more hospitable lower gastrointestinal tract for Campylobacter.

A series of experiments were conducted to evaluate the effects of ergot alkaloids (dihydroergotamine, ergonovine, and ergotamine) on E. coli O157:H7 in both pure and mixed ruminal fluid culture. Alkaloids were added to solutions of E. coli O157:H7 strains 933 (pure and ruminal cultures) and 6058 (ruminal culture only), and growth rates and colony-forming units (CFU) of E. coli O157:H7 were measured. Two mixtures of all three alkaloids at either 2 or 500 microM for each alkaloid decreased (p0.001) the growth rate of E. coli O157:H7 in pure culture compared to the individual alkaloids. Dihydroergotamine tended (p = 0.07) to reduce growth rate of E. coli O157:H7 in pure culture compared with ergonovine or ergotamine alone. Increased concentrations of dihydroergotamine and ergotamine decreased (p0.003) growth rate of E. coli O157:H7 but increasing concentrations of ergonovine did not influence (p0.10) E. coli O157:H7 growth rate. Similar to results in pure culture, a mixture of all three alkaloids at various concentrations for each alkaloid decreased (p0.001) the CFU of E. coli O157:H7 strain 6058 in mixed ruminal culture compared to the individual ergot alkaloids. Dihydroergotamine decreased (p = 0.04) CFU of E. coli O157:H7 strain 6058 when compared to ergonovine but CFU were similar (p0.10) between dihydroergotamine and ergotamine. Ruminal and (or) intestinal populations of E. coli O157:H7 may be influenced in livestock consuming endophyte-infected tall fescue, and these alterations could be due to the presence of ergot alkaloids in fescue plants.

Seasonal shedding of Escherichia coli O157:H7 in ruminants is well documented; however, viable explanations for this phenomenon are lacking. The fecal prevalence of E. coli O157:H7 in ruminants is the highest in the summer months, decreasing to low or undetectable levels in the winter. To determine if day length is correlated to seasonal shedding, nine reports of E. coli O157:H7 prevalence in cattle were selected for similarity of sampling technique, culture methodology, cattle type, and ability to determine approximate sampling month and location, representing three regions in North America (southern Canada, midwestern United States, and the southern United States/Mexico). Correlation and regression analysis revealed a positive correlation existed between day length (r = 0.67; R2 = 0.45; P = 0.0009) and, to a lesser extent, ambient temperature (r = 0.43; R2 = 0.19; P = 0.05) and E. coli O157:H7 prevalence. Based on these results, a study was conducted in a commercial feedlot to examine the effect of artificial lighting on E. coli O157 prevalence. Four pens of cattle received approximately 5 hours of artificial lighting daily (in addition to the natural light) for 60 days and four pens served as controls. Freshly voided fecal samples (representing approximately 30% of the steers/pen) were collected from the pen floor and cultured for E. coli O157 after 25 and 53 days of artificial lighting and 28 and 43 days following cessation of the lighting treatment. Fecal prevalence of E. coli O157 remained constant in the lighted pens whereas prevalence was lower (P0.01) in the control treatment after 53 days of lighting. Forty-three days following cessation of the lighting treatment, prevalence decreased in the lighted treatment group to levels comparable (P0.20) to control levels. Understanding the mechanisms underlying the seasonality of this important foodborne pathogen will enable the implementation of effective control strategies when it is most prevalent.

Escherichia coli O157:H7, Salmonella, and Listeria are foodborne pathogens of critical importance that often colonize cattle. E. coli O157:H7 can be specifically killed by lytic bacteriophage, and lytic bacteriophage treatment has been suggested as a pre-harvest intervention strategy to reduce foodborne pathogens in cattle. To date, no systematic approach to determine the incidence of E. coli O157:H7-infecting lytic bacteriophage has been published. Therefore, the current study was designed to determine (1) the incidence of E. coli O157, Salmonella spp., and Listeria and (2) the incidence of E. coli O157:H7-infecting bacteriophage in the feces of feedlot steers in commercial feedlots in the United States. Fecal samples (n=60) were collected from four feedlots in two Southern Great Plains states (total (n=240 fecal samples). Salmonella and E. coli O157:H7 were found in 3.8% and 11.7% of the fecal samples, respectively. Bacteriophage targeting E. coli O157:H7 were found in all four feedlots, in 15% of the individual fecal samples, and in 55% of the cattle pens. Our results indicate that such bacteriophage are widespread in feedlot cattle, suggesting that further research into the ecological role of bacteriophage in the gastrointestinal tract is needed.

Swine can harbor Salmonella in their gastrointestinal tracts. It has been estimated that up to 48% of the U.S. swine herd may carry Salmonella. Housing sows in farrowing stalls has become controversial due to animal welfare-based criticisms. An alternative production system is to keep sows outdoors on pasture with access to individual farrowing huts. This study was designed to determine the effects of two production systems on indicator bacteria and Salmonella of sows housed indoors in farrowing stalls (n = 52) compared to sows housed outdoors (n = 52) in English style huts. Each farrowing radial contained one wallow, from which mud (n = 290) and water (n = 290) samples were collected weekly. All samples were analyzed for generic E. coli, coliforms and Salmonella. No differences (p0.05) were detected in Salmonella, generic E. coli and coliform populations between indoor farrowing stalls and outdoor farrowing huts. However, all 8 outdoor wallows contained Salmonella spp. at some point during the study (n = 49 Salmonella isolates). Salmonella genotypes persisted within some wallows for5 months, and genetically indistinguishable Salmonella isolates were found in multiple wallows. Salmonella isolated from outdoor sow feces were genetically indistinguishable by PFGE from Salmonella isolated from wallows (n = 33) throughout the study, indicating that pathogenic bacteria were cycling between swine and their environment. In conclusion, the role of wallows in disseminating Salmonella within an outdoor swine herd appears to be significant.

Mature, healthy lactating dairy cattle were sampled on two farms in the southwestern United States to examine the effects of heat stress (Experiment I) and stage of lactation (Experiment II) on the fecal shedding of E. coli O157:H7 and Salmonella. To examine the effects of heat stress, fecal samples were collected from 45 cows at 7:00 AM (coolest part of the day) and 5:00 PM (hottest part of the day) in August 2002 on a 250 cow dairy. The study was replicated one month later (n = 170 total samples). A temperature-heat index (THI) was calculated for each sampling time. In Experiment II, stage of lactation was examined by sampling lactating dairy cattle early [60 days in milk (DIM)] and late (150 DIM) in the lactation cycle in the summer of 2001. The study was replicated the following summer (60 cows/group/replicate; n = 240 total samples). For Experiment I, THI averaged 75 and 82 for the AM and PM samplings, respectively, indicating the cows were beginning to experience heat stress in the morning and by afternoon were in severe heat stress. The shedding of E. coli O157:H7 tended to be higher (p = 0.09) in the afternoon sampling of the first replicate, however was not different in the second replicate or when both replicates were pooled (p0.10). Salmonella shedding was not different (p0.10) at any sampling time with nearly 100% of the cows positive. Stage of lactation had no effect on the number of cows shedding E. coli O157:H7 (p0.10). Salmonella shedding tended to be higher (p = 0.09) in early lactation cows in the first replicate, while in the second replicate more late lactation cows were shedding Salmonella (p0.05); however, there were no differences due to stage of lactation when replicates were pooled (p0.10). While further research is needed, results of this research highlight the variability in pathogen shedding in healthy dairy cattle and indicate that environmental factors and/or production demands may influence shedding patterns of E. coli O157:H7 and Salmonella.

The spread of antibiotic resistance from farm animals to human pathogens has become a matter of great public health significance, and methods to reduce foodborne pathogenic bacteria without utilizing traditional antibiotics have been sought. Chlorate kills Escherichia coli O157:H7 in vitro and in vivo and has been proposed as a feed additive to be included in food animal rations immediately prior to slaughter to reduce E. coli O157:H7 populations in the animal gastrointestinal tract. This study was designed to examine the effect that the development of chlorate resistance in E. coli O157:H7 has on resistance to 32 medically important antibiotics. Chlorate resistance numerically increased antibiotic resistance in E. coli O157:H7 strain 6058 and strain 933 to six and four antibiotics, respectively, but chlorate resistance affected resistance to only two antibiotics (cefoxotin and sulfadimethoxine) in both strains examined. Based on the fact that chlorate resistant mutants do not appear to compete well in vivo and based on the results of the current study, it appears unlikely that chlorate treatment will result in a dissemination of antibiotic resistance. However, further research is needed to confirm these results.

Zoonotic enteric pathogenic bacteria can live in the intestinal tract of birds and can be transmitted to food animals or humans via fecal contact. In the present study, cecal samples were collected from 376 migratory birds from species often associated with cattle during the fall migration in the Central Flyway of the United States. Brown-headed cowbirds (n=309, Molothrus ater), common grackles (n=51, Quiscalus quiscula), and cattle egrets (n=12, Bubulcus ibis) contained foodborne pathogenic bacteria in their ceca. Salmonella enterica was isolated from 14.9% of all samples, and Escherichia coli O157:H7 from 3.7%. Salmonella serotypes isolated included the following: Muenster, Montevideo, and Typhimurium. Our data suggest that migratory birds associated with cattle could be a vector for zoonotic enteric pathogenic bacteria to be disseminated across long distances.

Salmonella can live undetected in the gut of food animals and be transmitted to humans. Animal diets can impact intestinal populations of foodborne pathogens, including Salmonella spp. Orange juice production results in a waste product, orange peel and orange pulp, which has a high nutritive value and is often included in cattle diets as a least-cost ration ingredient. Here we show that the inclusion of orange peel products reduced Salmonella Typhimurium populations in the gut of experimentally inoculated sheep. Sheep (n=24) were fed a cracked corn grain-based high grain diet that was supplemented with a 50%/50% (dry matter [DM], w/w) mixture of dried orange pellet and fresh orange peel to achieve a final concentration (DM, basis) of 0%, 10%, or 20% orange product (OP) for 10 days before inoculation with Salmonella Typhimurium. Sheep were experimentally inoculated with 10(10) colony forming units Salmonella Typhimurium, and fecal samples were collected every 24 h after inoculation. Sheep were humanely euthanized at 96 h after oral Salmonella inoculation. Populations of inoculated Salmonella Typhimurium were numerically reduced by OP treatment throughout the gastrointestinal tract, and this reduction only reached significant levels in the cecum (p

The objectives of the current research were to determine the effect of weaning on fecal shedding of Salmonella and Escherichia coli O157:H7 in dairy calves and to examine cultured isolates (to include Enterococcus) for antimicrobial susceptibility. This research was conducted on one large commercial dairy (3000 head) in the southwestern United States. Two collections were made, during the winter (January 2009) and summer (July 2009) seasons. For the winter collection, two groups of calves were sampled (group 1: n = 18 pens, 69 head, ∼12 weeks of age; group 2: n = 19 pens, 75 head, ∼10 weeks of age). Fecal samples were collected from all calves via rectal palpation 2 days pre- and again 2 days postweaning. For the summer collection, one group of calves housed in 40 pens were utilized and 79 and 76 calves sampled 7 days pre- and 5 days postweaning, respectively. Fecal samples were collected into sterile palpation sleeves, placed on ice, and shipped to our laboratory for bacterial culture of E. coli O157:H7, Salmonella, and Enterococcus. Antimicrobial susceptibility was determined on select isolates. No differences (p 0.10) in prevalence of Salmonella or E. coli O157:H7 were observed due to weaning in the winter collection. In the summer collection, more (p 0.01) fecal samples were Salmonella positive preweaning (15.2%) as compared to postweaning (2.6%). No differences were observed for antimicrobial susceptibility in isolates collected pre- as compared to postweaning in either winter or summer collections, with the exception that multidrug-resistant Enterococcus faecium isolates preweaning were resistant to six antibiotics compared to seven or eight antibiotics postweaning (summer collection). Results of the current research indicate that the weaning of dairy calves does not increase the prevalence of pathogenic bacteria or substantially modify antimicrobial susceptibility profiles of these bacteria.

The current research examined the inclusion of 20% wet distiller's grains (WDG) fed with steam-flaked corn (SFC) or dry-rolled corn (DRC) in diets fed to feedlot cattle on fecal prevalence of Escherichia coli O157:H7 and Salmonella. Crossbred beef heifers (n = 272; average initial body weight (BW) = 354 kg) were blocked by BW and pen size and randomly assigned to treatment. Fecal samples from freshly voided fecal pats were collected from each pen on the day cattle shipped for slaughter (237 fecal samples: 72, 125, and 40 from cattle 132, 160, and 181 days on feed, respectively). Fecal samples were cultured quantitatively and qualitatively for the above pathogens. Populations of E. coli O157:H7 and Salmonella were generally low with very few samples containing quantifiable populations. Similarly, after enrichment, few samples were E. coli O157:H7 positive in any collection with no treatment differences (p0.10). More samples were Salmonella positive during the first collection with an increased (p0.05) prevalence observed in the SFC and DRC treatments compared with DRC + WDG treatment. No other treatment differences were observed for Salmonella. Putative fecal coliform isolates (18 per treatment; first collection) were examined for antimicrobial susceptibility, and the majority were susceptible to all of the antibiotics examined. Most of the resistance was observed in the SFC (n = 3) and DRC (n = 4) treatments, and only one isolate in each of the two WDG treatments demonstrated resistance (one antibiotic each, streptomycin and tetracycline). All multidrug resistance (2-4 antibiotics) was observed in isolates cultured from the DRC and SFC treatments (n = 2 isolates in each treatment). Results of the current research found no significant effect of feeding WDG to feedlot cattle on fecal prevalence, at time of shipment for slaughter, of E. coli O157:H7, and only modest differences (decreases) in Salmonella prevalence with no apparent affect on antimicrobial susceptibility of fecal coliform isolates.

The objective of the current research was to determine if exogenous melatonin would exert a "protective" effect on the gastrointestinal tract of sheep and prevent or reduce the horizontal transfer of Escherichia coli O157:H7 from experimentally infected to noninfected or "naïve" sheep. Sixteen cross-bred ewes were housed indoors and adapted to a high concentrate ration. Ewes were randomly assigned to one of four rooms and treatment (three ewes/room, six ewes/treatment) and received either control (gelatin capsule only) or melatonin (5.0 mg/kg body weight [BW]/d). Four additional ewes served as "carrier" sheep (one/room) and were experimentally infected via oral gavage with E. coli O157:H7. Three days post-challenge, carrier ewes were housed with naïve sheep and remained with them for the remainder of the experimental period. Treatments were administered to the naïve sheep 1 day prior to introduction of the carrier sheep and on each of the remaining 7 days of the experimental period. Fecal samples were collected via rectal palpation from the carrier sheep daily throughout experiment and from the naïve sheep daily for 5 days, starting 2 days following introduction of the carriers. On day 8 of the experiment, all ewes were euthanized and tissues from the rumen, ileum, cecum, colon, and rectum as well as their respective lumen contents collected. The carrier sheep quickly infected the naïve ewes, which had similar fecal concentrations as the carrier animals throughout the 5-day sampling period. Melatonin treatment had no effect (p0.10) on daily fecal shedding, luminal content concentrations, or in the percentage of gastrointestinal tract tissue positive for the inoculated strain of E. coli O157:H7.

Composting manure, if done properly, should kill pathogenic bacteria such as Salmonella and Escherichia coli O157:H7, providing for an environmentally safe product. Over a 3-year period, samples of composted dairy manure, representing 11 composting operations (two to six samples per producer; 100 total samples), were screened for Salmonella and E. coli O157:H7 and were all culture negative. Nonpathogenic bacteria were cultured from these compost samples that could theoretically facilitate the spread of antimicrobial resistance from the dairy to compost application sites. Therefore, we collected soil samples (three samples per plot; 10 plots/treatment; 90 total samples) from rangeland that received either composted dairy manure (CP), commercial fertilizer (F), or no treatment (control, CON). Two collections were made appoximately 2 and 7 months following treatment application. Soil samples were cultured for Pseudomonas and Enterobacter and confirmed isolates subjected to antimicrobial susceptibility testing. Three species of Enterobacter (cloacae, 27 isolates; aeroginosa, two isolates; sakazakii, one isolate) and two species of Pseudomonas (aeruginosa, 11 isolates; putida, seven isolates) were identified. Five Enterobacter isolates were resistant to ampicillin and one isolate was resistant to spectinomycin. All Pseudomonas isolates were resistant to ampicillin, ceftiofur, florfenicol, sulphachloropyridazine, sulphadimethoxine, and trimethoprim/sulfamethoxazole and most isolates were resistant to chlortetracycline and spectinomycin. Pseudomonas isolates were resistant to an average of 8.6, 7.9, and 8 antibiotics for CON, CP, and F treatments, respectively. No treatment differences were observed in antimicrobial resistance patterns in any of the soil isolates examined. Results reported herein support the use of composted dairy manure as an environmentally friendly soil amendment.

Orange peel and orange pulp are by-products that are included in feedlot and dairy cattle diets because of their low cost and high nutritional quality. The antimicrobial activity of citrus oils has been reported previously. The present study was carried out to determine whether these citrus by-products exert antimicrobial effects on Escherichia coli O157:H7 and Salmonella Typhimurium populations that are found in cattle gastrointestinal tracts. The growth of pure cultures (n = 3) of E. coli O157:H7 and Salmonella Typhimurium were reduced (p0.05) by addition of 2% (w/v) orange pulp and orange peel. Ruminal fluid was collected from cattle (n = 2) and E. coli O157:H7 or Salmonella Typhimurium were added. The addition of orange pulp and peel to in vitro mixed ruminal microorganism fermentations (n = 3) demonstrated that both orange pulp and peel reduced E. coli O157:H7 and Salmonella Typhimurium populations at least 2 log(10) in mixed ruminal fluid fermentations. Addition of orange pulp reduced (p0.05) E. coli O157:H7 populations from 10(5) to 10(2) colony-forming units (CFU)/mL and Salmonella Typhimurium populations (p0.05) from 10(4) to 10(2) CFU/mL. These results indicate that orange pulp and/or peel included in ruminant diets could decrease ruminal populations of foodborne pathogenic bacteria. Further research is needed to determine whether the antimicrobial activity of orange products against E. coli O157:H7 or Salmonella Typhimurium is expressed in the lower gastrointestinal tract.

Escherichia coli O157:H7 can live undetected in the gut of food animals and be spread to humans directly and indirectly. Bacteriophages are viruses that prey on bacteria, offering a natural, nonantibiotic method to reduce pathogens from the food supply. Here we show that a cocktail of phages isolated from commercial cattle feces reduced E. coli O157:H7 populations in the gut of experimentally inoculated sheep. A cocktail of phages was used in order to prevent the development of resistance to the phages. In our first in vivo study we found that our cocktail of phages reduced E. coli O157:H7 populations in the feces of sheep (p0.05) by 24 hours after phage treatment. Upon necropsy, populations of inoculated E. coli O157:H7 were reduced by phage treatment in both the cecum (p0.05) and rectum (p0.1). In our second in vivo study, several ratios of phage plaque-forming units (PFU) to E. coli O157:H7 colony-forming units (CFU) were used (0:1, 1:1, 10:1, and 100:1 PFU/CFU) to determine the most efficacious phage dose. A 1:1 ratio of phage to bacteria was found to be more effective (p0.05) than either of the higher ratios used (10:1 or 100:1). Ruminal levels of E. coli O157:H7 were not significantly reduced (p0.10) in any of the studies due to relatively low inoculated E. coli O157:H7 ruminal populations. Our results demonstrate that phage can be used as a preharvest intervention as part of an integrated pathogen reduction scheme.

To examine the effect of ionophore supplementation on fecal shedding of Escherichia coli O157:H7 and Salmonella, crossbred beef calves (n=113; mean body weight [BW], 243 kg) were fed a mineral supplement with ionophore (1.76 g lasalocid/kg) for 61 days (d). Control calves received an identical mineral supplement without lasalocid. Calves were pastured on fescue/bermudagrass paddocks and supplemented with a corn/wheat midds/soybean meal supplement (1.5% of BW/d). Upon arrival, cattle were fed a commercial receiving ration containing 1 g chlorotetracycline/kg for 10 d. Sick calves were administered one or a combination of the following: Nuflor (florfenicol), Baytril (eurofloxacin), Micotil (tilmicosin), or LA 200 (oxytetracycline). Fecal samples were collected immediately prior to ionophore supplementation, approximately midway and at the end of the experimental period (60 d total ionophore feeding) for isolation of E. coli O157:H7 and Salmonella. Putative fecal coliforms were also isolated at these sampling times and examined for antimicrobial susceptibility. The study was replicated over a two year period (year 1, n=53 head; year 2, n=60 head). Ionophore supplementation had no effect (p0.10) on the incidence of calves shedding E. coli O157:H7 or Salmonella. The percentage of calves shedding E. coli O157:H7 varied throughout the experimental period from 0 to 30%, while Salmonella was cultured from only three calves over the 2-year experimental period. Antimicrobial susceptibility profiles of putative fecal coliforms were consistent with antibiotic treatments administered during the study (observed resistance to chlortetracycline, florfenicol, oxytetracycline), while only one treatment effect was observed. Ionophore treatment resulted in a significantly higher number of coliform isolates resistant to ampicillin compared to controls in year 1, but not year 2. A number of fecal coliform isolates demonstrated resistance to multiple antibiotics, however, this was not affected (p0.10) by ionophore supplementation. Mineral intakes, BW gain, and the number of sick calves were similar (p0.10) among treatments. Ionophore supplementation had no affect on fecal shedding of E. coli O157:H7 or Salmonella and a negligible impact on antimicrobial susceptibility patterns of fecal coliforms in beef calves.

Six 1-ha paddocks of tall fescue (Festuca arundinacea) grazed by Gelbvieh x Angus heifers from 1 March to 21 June 2005 were used to determine the prevalence of Escherichia coli O157:H7 and Salmonella in water tanks, and standing water and surface soil surrounding water tanks in tall fescue paddocks grazed by cattle. Paddocks included two each of Kentucky-31 endophyte-infected tall fescue (E+), Jesup tall fescue with the AR542 endophyte strain (MaxQ), and HiMag tall fescue with strain 4 endophyte (HiMag4). Samples were collected weekly (6 June to 5 July) from water tanks (n = 30), and standing water (n = 18) and surface soil (n = 30) surrounding the water tanks in each paddock commencing 3 weeks prior to termination of grazing until 2 weeks after cattle removal. Prevalence of E. coli O157:H7 tended (p = 0.07) to be increased in standing water and surface soil surrounding water tanks when cattle were present. Presence of cattle resulted in muddy conditions surrounding water tanks. Consumption of E+ tall fescue did not influence (p0.10) the prevalence of E. coli O157:H7 or Salmonella in or around water tanks. Neither E. coli O157:H7 or Salmonella were detected in water tanks. Total percentage of standing water samples positive for E. coli O157:H7 was 27.8% and 5.6% for Salmonella. Escherichia coli O157:H7 (6.7%) and Salmonella (10%) also were detected in the surface soil surrounding the water tanks. We conclude that areas surrounding water tanks in tall fescue paddocks can be reservoirs of pathogenic bacteria.