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The disinfectant and antimicrobial susceptibility profiles of 138 non-O157 Shiga toxin–producing Escherichia colistrains (STECs) from food animals and humans were determined. Antimicrobial resistance (AMR) was moderate (39.1% of strains) in response to 15 antimicrobial agents. Animal strains had a lower AMR prevalence (35.6%) than did human strains (43.9%) but a higher prevalence of the resistance profile GEN-KAN-TET. A decreasing prevalence of AMR was found among animal strains from serogroups O45 > O145 > O121 > O111 > O26 > O103 and among human strains from serogroups O145 > O103 > O26 > O111 > O121 > O45. One animal strain from serogroups O121 and O145 and one human strain from serogroup O26 had extensive drug resistance. A high prevalence of AMR in animal O45 and O121 strains and no resistance or a low prevalence of resistance in human strains from these serogroups suggests a source other than food animals for human exposure to these strains. Among the 24 disinfectants evaluated, all strains were susceptible to triclosan. Animal strains had a higher prevalence of resistance to chlorhexidine than did human strains. Both animal and human strains had a similar low prevalence of low-level benzalkonium chloride resistance, and animal and human strains had similar susceptibility profiles for most other disinfectants. Benzyldimethylammonium chlorides and C10AC were the primary active components in disinfectants DC&R and P-128, respectively, against non-O157 STECs. A disinfectant FS512 MIC ≥ 8 μg/ml was more prevalent among animal O121 strains (61.5%) than among human O121 strains (25%), which may also suggest a source of human exposure to STEC O121 other than food animals. Bacterial inhibition was not dependent solely on pH but was correlated with the presence of dissociated organic acid species and some undissociated acids.

AbstractThe aim of this study was to assess the efficacy of a combination of sorbic acid, thymol, and carvacrol in reducing the prevalence and shedding level of SalmonellaTyphimurium in pigs either in a controlled challenge environment or in a production setting. In the first study, 24 weaned piglets were separated in 4 isolation units (6 piglets/isolation unit). Each unit received either a basal diet (no treatment) or a microencapsulated mixture of sorbic acid, thymol, and carvacrol at 1, 2, or 5 g/kg of feed. After 21 d, pigs were orally challenged with 6 log10colony-forming units of SalmonellaTyphimurium. Blood samples and feces from rectal ampullae were collected every week. On d56 of the study, pigs were euthanized and necropsied to collect intestinal contents (jejunum through colon) and ileocecal lymph nodes. Samples were analyzed for SalmonellaTyphimurium and serological analysis was also conducted. In the second study, an all-in-all-out multisite pig farm that was positive for monophasic SalmonellaTyphimurium was followed throughout a production cycle from weaning to slaughter. Pigs received either a basal diet or the basal diet including 5 g/kg of the microencapsulated additive. Environmental, fecal, and blood samples were collected monthly, and cecal contents and ileocecal lymph nodes were collected at slaughter to isolate and enumerate Salmonella. The results indicate that the additive at 5 g/kg tended to reduce Salmonellafecal prevalence in both a controlled challenge (p=0.07) and in production conditions (p=0.03). Nevertheless, the additive did not reduce the number of pigs seropositive for Salmonella, nor it reduced the Salmonellaprevalence at slaughter. The data indicate that these additives are not effective alone but must be used in conjunction with appropriate containment measures at lairage in order to prevent reinfection in pigs and to reduce the number of pigs carrying Salmonellaentering the food chain.

AbstractEscherichia coliO157:H7 is a foodborne pathogen that causes illness in humans worldwide. Cattle are the primary reservoir of this bacterium, with the concentration and frequency of E. coliO157:H7 shedding varying greatly among individuals. The term “super-shedder” has been applied to cattle that shed concentrations of E. coliO157:H7≥104colony-forming units/g feces. Super-shedders have been reported to have a substantial impact on the prevalence and transmission of E. coliO157:H7 in the environment. The specific factors responsible for super-shedding are unknown, but are presumably mediated by characteristics of the bacterium, animal host, and environment. Super-shedding is sporadic and inconsistent, suggesting that biofilms of E. coliO157:H7 colonizing the intestinal epithelium in cattle are intermittently released into feces. Phenotypic and genotypic differences have been noted in E. coliO157:H7 recovered from super-shedders as compared to low-shedding cattle, including differences in phage type (PT21/28), carbon utilization, degree of clonal relatedness, tirpolymorphisms, and differences in the presence of stx2a and stx2c, as well as antiterminator Q gene alleles. There is also some evidence to support that the native fecal microbiome is distinct between super-shedders and low-shedders and that low-shedders have higher levels of lytic phage within feces. Consequently, conditions within the host may determine whether E. coliO157:H7 can proliferate sufficiently for the host to obtain super-shedding status. Targeting super-shedders for mitigation of E. coliO157:H7 has been proposed as a means of reducing the incidence and spread of this pathogen to the environment. If super-shedders could be easily identified, strategies such as bacteriophage therapy, probiotics, vaccination, or dietary inclusion of plant secondary compounds could be specifically targeted at this subpopulation. Evidence that super-shedder isolates share a commonality with isolates linked to human illness makes it imperative that the etiology of this phenomenon be characterized.

AbstractFoodborne 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 coliO157:H7 and SalmonellaTyphimurium. Pure cultures (2×106colony-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. coliO157:H7 and SalmonellaTyphimurium in pure culture at concentrations >2%. E. coliO157:H7 and SalmonellaTyphimurium were added (2×105and 3×106CFU/mL, respectively) to in vitromixed 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. coliO157:H7 and SalmonellaTyphimurium in the ruminal fluid at concentrations ≥5%. The acetate–to-propionate ratios from the in vitrofermentations 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.

AbstractZoonotic 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 entericawas isolated from 14.9% of all samples, and Escherichia coliO157:H7 from 3.7%. Salmonellaserotypes 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.

AbstractResearchers have documented that the housefly (Musca domestica) can serve as a vector for the spread of foodborne pathogens to livestock, food, and humans. Most studies have investigated Musca domesticaas a vector only after the fly comes into contact or consumes the pathogen as an adult. The objective of this study was to determine whether the larvae of Musca domesticacould ingest Escherichia colifrom bovine manure and whether the E. colicould survive the metamorphosis process and be transmitted. Larvae (n=960) were incubated in sterilized bovine manure inoculated with 0, 3, 5, and 8 log10colony-forming units (CFU)/mL of bioluminescent E. colifor 24 (larvae stage), 48 (larvae stage), 120 (pupae stage), and 192 h (adult stage). Larvae incubated for 24 h in bovine manure possessed 0.0, 2.7, 2.9, and 3.5 log10CFU/mL of E. coli, from inoculated with 0, 3, 5, and 8 log10CFU/mL of E. coli,respectively. Concentrations of E. coliwithin the pupae were 0.0, 1.7, 1.9, and 2.2 log10CFU/mL for each inoculation concentration, respectively. Flies that emerged from the pupae stage contained 0.0, 1.3, 2.2, and 1.7 log10CFU/mL of E. colifrom larvae incubated in manure inoculated with concentrations of E. coli, respectively. These results suggest the housefly can emerge with quantities of E. coli. While this was an enteropathogenic E. coli(EPEC), these data may suggest that if the fly is capable of retaining similar concentrations of an enterohemorrhagic E. coli(EHEC), these concentrations may be capable of initiating illness in humans. Furthermore, the E. coliconcentration within and on adult flies is related to environmental exposure. It must be noted that larvae were incubated in sterilized bovine manure, and there was no other bacterial competition for the E. coli. Thus, the rate of positive flies and concentrations present when flies emerged may vary under more realistic conditions.

AbstractThe use of luminescent plasmids in bacteria may serve as a viable model for the real-time validation of various pre-harvest interventions on the colonization or shedding patterns of Escherichia coliO157:H7 within cattle. The objective of this study was to determine if the growth characteristics of E. coliO157:H7 in mixed ruminal and fecal microbial fluid cultures would be altered when transformed with one of the two luminescent plasmids: pAK1-lux(PAK) or pXEN-13 (XEN). Transformants harboring the luminescent plasmids were compared to the non-transformed parental strain (wild type [WT]) after incubating in mixed ruminal or fecal microbial fluid media for 6 h in triplicate (n=3). The transformants and WT exhibited similar growth rates. Within mixed ruminal microbial fluid fermentations and mixed fecal microbial fluid, all transformants grew similarly (p=0.28) through the 6-h study. The reflective light unit (RLU; photons/pixel per second) photonic emissions of each plasmid within ruminal fluid differed at 0 h (p=0.002) and 2 h (p=0.02) and within fecal fluid at 0 h (p=0.009) and 2 h (p=0.04). The RLU remained the same within rumen fluid at 4 h (p=0.22) and 6 h (p=0.80) and within fecal fluid at 4 h (p=0.06) and 6 h (p=0.29). Growth of E. coliO157:H7 transformed with the bioluminescent plasmids was not altered in comparison to the WT, suggesting that both plasmids may serve as useful models for in vivostudies.

AbstractWhile Shiga toxin–producing Escherichia coli(STEC) reside asymptomatically within ruminants, particularly cattle, these strains pose a serious health risk to humans. Research related to STEC has historically focused upon O157:H7. However, with an increase in foodborne outbreaks of non-O157 origin and recent changes in testing for non-O157 by the U.S. Department of Agriculture Food Safety and Inspection Service (USDA-FSIS), there is now a critical need to understand the biological activity of non-O157 serogroups. The focus of this study was to determine whether variations exist in the ability of different serotypes of STEC to survive within bovine rumen fluid medium and bile salts. The results of this study demonstrated through viable plate count analysis that the five serotypes tested (O157:H7, O111:H8, O103:K.:H8, O145:H28, and O26:H11) were capable of growing in rumen fluid medium. However, the concentrations of the serotypes O103:K.:H8 and O26:H11 after 24 h were significantly less (p<0.05) than that observed for the other serotypes tested. A significant decrease (p=0.03) in the survival of O103:K.:H8 in 50 mg/mL of bovine bile salts in comparison to the other STEC strains tested was also observed. Collectively, these data suggest that non-O157 serogroups of E. colirespond differently to the environment of the bovine gastrointestinal tract. Further research is needed to elucidate how these differential physiological variations correlate with alterations in colonization success within ruminants and how they may impact human illnesses.

AbstractReducing Salmonellain poultry has been a paramount goal of the poultry industry in order to improve food safety. Inclusion of high-fiber fermentable feedstuffs in chicken diets has been shown to reduce the incidence of Salmonellacolonization in laying hens, but no work has been performed in growing birds. Therefore, the present study was designed to quantify differences in artificially inoculated cecal SalmonellaTyphimurium populations in growing layer chicks (n=60 in each of two replications) fed 0%, 25%, and 50% of their diet (w/w) replaced with alfalfa meal from day (d) 7 to d14 after hatch. Alfalfa supplementation reduced cecal populations of Salmonellaby 0.95 and 1.25 log10colony-forming unit per gram in the 25% and 50% alfalfa groups compared to controls. Alfalfa feeding reduced (p<0.05) the number of cecal- and crop-positive birds compared to controls. Increasing levels of alfalfa increased (p<0.05) total volatile fatty acids (VFA) and the proportion of acetate in the cecum. Surprisingly, alfalfa inclusion did not negatively impact average daily gain (ADG) in birds over the 7-d feeding period. Alfalfa inclusion at 50% of the diet increased (p<0.05) the number of bacterial genera detected in the cecum compared to controls, and also altered proportions of the microbial population by reducing Ruminococcusand increasing Clostridiapopulations. Results support the idea that providing a fermentable substrate can increase gastrointestinal VFA production and bacterial diversity which in turn can reduce colonization by Salmonellavia natural competitive barriers. However, further studies are obviously needed to more fully understand the impact of changes made in diet or management procedures on poultry production.

Food producing animals can be reservoirs of Campylobacter, a leading bacterial cause of human foodborne illness. Campylobacterspp. utilize amino acids as major carbon and energy substrates, a process that can be inhibited by thymol and diphenyliodonium chloride (DIC). To determine the effect of these potential additives on feed intake, live weight gain, and gut Campylobacterlevels, growing pigs were fed standard grower diets supplemented with or without 0.0067 or 0.0201% thymol or 0.00014 or 0.00042% DIC in a replicated study design. Diets were offered twice daily for 7 days, during which time daily feed intake (mean ± SEM, 2.39 ± 0.06 kg day–1) and daily gain (0.62 ± 0.04 kg day–1) were unaffected (P> 0.05) by treatment. Pigs treated with DIC but not thymol tended to have lower rectal Campylobacterlevels (P= 0.07) (5.2 versus 4.2 and 4.4 log CFU g−1rectal contents for controls and 0.00014% DIC and 0.00042% DIC, respectively; SEM = 0.26). However, DIC or thymol treatments did not affect (P> 0.05) ileal or cecal Campylobacter(1.6 ± 0.17 and 4.5 ± 0.26 log CFU g−1, respectively), cecal total culturable anaerobes (9.8 ± 0.10 log CFU g−1), or accumulations of major fermentation end products within collected gut contents. These results suggest that thymol and DIC were appreciably absorbed, degraded, or otherwise made unavailable in the proximal alimentary tract and that encapsulation technologies will likely be needed to deliver effective concentrations of these compounds to the lower gut to achieve in vivo reductions of Campylobacter.

Three experiments were conducted to evaluate the influence of vitamin D on fecal shedding of Escherichia coliO157:H7 in cattle. In the first experiment, two groups of cattle (beef and dairy) were assigned to a control treatment or to receive 0.5 x 106IU vitamin D per day via oral bolus for 10 days. Fecal samples were collected before and throughout the dosing period for culture of E. coliO157:H7. No differences were observed for fecal shedding of E. coliO157:H7 among treatments for either beef or dairy animals. Serum concentrations of vitamin D were markedly higher (P< 0.0001) in treated beef cattle but only tended to be higher (P = 0.09) in the dairy cattle. In the second experiment, three successive vitamin D dosages (2,400, 4,800, and 9,600 IU/day; 14 days each) were administered to 14 dairy steers (7 steers served as controls), fecal samples were collected daily, and serum samples were collected weekly throughout the 42-day experimental period. No significant differences in fecal prevalence or serum vitamin D concentrations were observed for any of the vitamin D dosages. A third experiment sampled feedlot cattle (winter and summer) to determine whether serum vitamin D concentrations were correlated with fecal shedding of E. coliO157:H7. A fecal sample and a blood sample were obtained in each season from 60 randomly selected animals (total of 120 fecal samples and 120 corresponding blood samples). As expected, season was highly correlated (r = 0.66) with serum vitamin D concentration with higher concentrations (P< 0.01) observed in the summer. E. coliO157:H7 prevalence (percentage of positive samples) was not highly correlated (r = 0.16) with season, although the correlation tended to be significant (P = 0.08). The proportion of cattle shedding E. coliO157:H7 was 16.7 and 6.7% for the summer and winter collections, respectively. Results of this research do not support a correlation between vitamin D intake and E. coliO157:H7 shedding in cattle.

Foodborne pathogenic bacteria such as Escherichia coliO157:H7 are threats to the safety of beef. Citrus peel and dried orange pulp are by-products from citrus juice production that have natural antimicrobial effects and are often incorporated into least-cost ration formulations for beef and dairy cattle. This study was designed to determine if orange peel and pulp affected E. coliO157:H7 populations in vivo. Sheep (n =24) were fed a cracked corn grain-based diet that was supplemented with a 50-50 mixture of dried orange pellet and fresh orange peel to achieve a final concentration (dry matter basis, wt/wt) of 0, 5, or 10% pelleted orange peel (OP) for 10 days. Sheep were artificially inoculated with 1010CFU of E. coliO157:H7 by oral dosing. Fecal shedding of E. coliO157:H7 was measured daily for 5 days after inoculation, after which all animals were humanely euthanized. At 96 h postinoculation, E. coliO157:H7 shedding was reduced (P <0.05) in sheep fed 10% OP. Populations of inoculated E. coliO157:H7 were reduced by OP treatment throughout the gastrointestinal tract; however, this reduction reached significant levels in the rumen (P < 0.05) of sheep fed 10% OP diets. Cecal and rectal populations of E. coliO157:H7 were reduced (P < 0.05) by inclusion of both 5 and 10% OP diets. Our results demonstrate that orange peel products can be used as a preharvest intervention strategy as part of an integrated pathogen reduction scheme.

AbstractSalmonellacan live undetected in the gut of food animals and be transmitted to humans. Animal diets can impact intestinal populations of foodborne pathogens, including Salmonellaspp. 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 SalmonellaTyphimurium 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 SalmonellaTyphimurium. Sheep were experimentally inoculated with 1010colony forming units SalmonellaTyphimurium, and fecal samples were collected every 24 h after inoculation. Sheep were humanely euthanized at 96 h after oral Salmonellainoculation. Populations of inoculated SalmonellaTyphimurium were numerically reduced by OP treatment throughout the gastrointestinal tract, and this reduction only reached significant levels in the cecum (p<0.05) of sheep fed 10% OP diets. Apparent palatability issues decreased the consumption of OP in sheep fed 20% OP to intake levels below that of 10% OP (approximately 7% dry matter intake [DMI]/d feed refusal), thereby reducing the potential effects of OP feeding at this higher level. Our results demonstrate that orange peel and pellets are environmentally friendly and low-cost products that can be used as a pre-harvest intervention as part of an integrated pathogen reduction scheme.

AbstractIt is thought that antimicrobial resistance imposes a fitness cost on bacteria, so that a reduction in antimicrobial use may reduce the incidence of resistant bacteria. The objectives of the present study were to determine (1) whether multidrug resistant (MDR) Escherichia colifield strains with different plasmid profiles show disparate plasmid loss when grown over time without selection pressure; (2) whether the number of plasmids present in the cell affects growth. Nine β-hemolytic E. colistrains from swine (n= 8) and cattle (n= 1) were grown in separate continuous-flow vessels for 36 days without antimicrobial selection. Populations were enumerated on brain heart infusion agar and brain heart infusion agar with tetracycline on days 2, 5, 8, 15, 22, 29, and 36. Growth rates, plasmid profiles and susceptibility profiles of the strains were compared, and day 36 isolates (n= 40, five for each MDR strain) were compared with their corresponding day 0 strains. Plasmid content of the nine field strains ranged from zero to eight with sizes from 3.2 to 165 kb. Changes in susceptibility profiles of day 36 isolates were observed among 20% (8 of 40) of the isolates. MDR E. colilargely maintained their original plasmid profiles, replicon types, and susceptibility profiles over 36 days of continuous culture. There was no significant difference in maximum specific growth rate among strains when compared with the plasmid-free strain or when day 36 isolates were compared with their own day 0 strain. This suggests that there is little fitness cost in the maintenance of multiple plasmids of various sizes under the conditions of this study. Other strategies rather than merely reducing antimicrobial usage are needed to combat the emergence of MDR bacteria.

AbstractSalmonellais 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 Salmonellalevels in the live animal. The present study was designed to determine if anti-Salmonellaphages isolated from the feces of commercial finishing swine could reduce gastrointestinal populations of the foodborne pathogen SalmonellaTyphimurium in artificially inoculated swine. Weaned pigs (n= 48) were randomly assigned to two treatment groups (control or phage-treated). Each pig was inoculated with SalmonellaTyphimurium (2 × 1010colony 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 × 109plaque 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 Salmonellapopulations in phage-treated pigs were lower (p< 0.09) than controls after 48 h. Phage treatment reduced intestinal populations of inoculated SalmonellaTyphimurium in pigs compared to controls at necropsy. Cecal populations were reduced (p= 0.07) by phage treatment >1.4 log10colony forming units/g digesta, and rectal populations were numerically reduced. The number of pigs that contained inoculated SalmonellaTyphimurium 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 Salmonellain swine. Further research needs to be performed to determine the most efficacious dosing regimens and the most effective combinations of phages targeting the diverse Salmonellapopulation found in swine before they can enter the food supply.

AbstractThe existence of two separate genetic lineages of Escherichia coliO157:H7 has previously been reported, and research indicates that lineage I could be more pathogenic toward human hosts than lineage II. We have previously shown that lineage I as a group expresses higher levels of Shiga toxin 2 (Stx2) than lineage II. To help evaluate why lineage II strains do not express appreciable levels of this toxin, whole-genome microarrays were performed using Agilent custom microarrays. Gene expression of the two representative bovine lineage II strains (FRIK966 and FRIK2000) were compared with gene expression of E. coliO157:H7 EDL933 (lineage I clinical type strain). Missing or differentially expressed genes and pathways were identified. Quantitative reverse transcription–polymerase chain reaction was performed to validate the microarray data. Draft genomes of FRIK966 and FRIK2000 were sequenced using Roche Applied Science/454 GS-FLX technology shotgun and paired-end approaches followed by de novoassembly. These assemblies were compared with the lineage I genome sequences from E. coliO157:H7 EDL933. The bacteriophage 933W, which encodes the Stx2 genes, showed a notable repression in gene expression. Polymerase chain reaction primers, based upon EDL933 genomic information, were also designed against all of the potentially missing genes of this bacteriophage. Most of the structural genes associated with the bacteriophage were found to be absent from the genome of the two bovine strains. These analyses, combined with evaluation of the genomic information, suggest that transposon (IS629) rearrangements may be associated with disruption of the bacteriophage genome in the FRIK strains. The results support the hypothesis that lineage II strains may be less of a risk as human foodborne pathogens. The microarray and genome data have been made available to the scientific community to allow continuing analysis of these cattle-isolated lineage II genomes and their gene expression.

AbstractSalmonellais one of the leading causes of human foodborne illness and is associated with swine production. Bacteriophages are naturally occurring viruses that prey on bacteria and have been suggested as a potential intervention strategy to reduce Salmonellalevels in food animals on the farm and in the lairage period. If phages are to be used to improve food safety, then we must understand the incidence and natural ecology of both phages and their hosts in the intestinal environment. This study investigates the incidence of phages that are active against Salmonellaspp. in the feces of commercial finishing swine. Fecal samples (n= 60) were collected from each of 10 commercial swine finishing operations. Samples were collected from 10 randomly selected pens throughout each operation; a total of 600 fecal samples were collected. Salmonellaspp. were found in 7.3% (44/600) of the fecal samples. Bacteriophages were isolated from fecal samples through two parallel methods: (1) initial enrichment in SalmonellaTyphimurium; (2) initial enrichment in Escherichia coliB (an indicator strain), followed by direct spot testing against SalmonellaTyphimurium. Bacteriophages active against SalmonellaTyphimurium were isolated from 1% (6/600) of the individual fecal samples when initially enriched in SalmonellaTyphimurium, but E. coliB-killing phages were isolated from 48.3% (290/600) of the fecal samples and only two of these phages infected SalmonellaTyphimurium on secondary plating. Collectively, our results indicate that bacteriophages are widespread in commercial swine, but those capable of killing SalmonellaTyphimurium may be present at relatively low population levels. These results indicate that phages (predator) populations may vary along with Salmonella(prey) populations; and that phages could potentially be used as a food safety pathogen reduction strategy in swine.

AbstractThe 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 coliO157: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. coliO157:H7 and Salmonellawere generally low with very few samples containing quantifiable populations. Similarly, after enrichment, few samples were E. coliO157:H7 positive in any collection with no treatment differences (p> 0.10). More samples were Salmonellapositive during the first collection with an increased (p< 0.05) 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. coliO157:H7, and only modest differences (decreases) in Salmonellaprevalence with no apparent affect on antimicrobial susceptibility of fecal coliform isolates.