38 Evaluation of Sorghum Phenolic Compounds for Their Antimicrobial Activities Against Liver Abscess Causing Pathogens in Feedlot Cattle

Liver abscesses occur in finishing cattle fed high-grain, low-roughage diets. Cattle with abscessed livers seldom show any clinical signs and are detected only at the time of slaughter. Liver abscesses are of significant economic concern to the feedlot industry. Liver abscesses comprise, on average, 67% of all liver abnormalities in cattle slaughtered in the United States with a prevalence of 10–20% and may reduce the value of the beef carcass up to $38 per animal with the most severe abscesses. There are four causative agents of the disease including the two subspecies of Fusobacterium necrophorum, ssp. necrophorum and ssp. funduliforme, Trueperella pyogenes, and Salmonella enterica. Tylosin, supplemented in the feed, is the most commonly used antibiotic in the feedlot industry to prevent liver abscesses. Because of the concerns about antimicrobial resistance, there is a need to find an effective alternative to this antibiotic, and sorghum grain extracts, which are high in phenolic compounds, may have the potential to be used as natural antibiotic alternatives. Our objectives were to investigate the efficacy of phenolic extracts from black, sumac, brown, and burgundy sorghums on liver abscess pathogens. The sorghum phenolics were extracted using 75% aqueous acetone and total phenolic content was determined by spectrophotometrically. Bacterial strains were cultured in Mueller-Hinton broth (Salmonella and Trueperella pyogenes) or anaerobic brain-heart infusion broth (Fusobacterium) with and without sorghum extracts (1 mg/ml) at 12, 24, and 48 hours and bacterial concentrations were determined. If the compound was inhibitory, a micro-broth dilution method was used to quantify the inhibitory activity. Both black and sumac sorghum phenolics inhibited growth of all four bacterial species. Further studies are ongoing to investigate different concentrations and phenolic compounds from varieties of sorghum grains on the liver abscess pathogens.

48 Evaluation of Antimicrobial Activities of Phytophenols Against Bacterial Pathogens That Cause Liver Abscesses in Feedlot Cattle

Liver abscesses occur in finishing cattle fed high-grain, low-roughage diets. Cattle with abscessed livers do not show any clinical signs and are detected only at slaughter. Liver abscesses, which account for 67% of all liver abnormalities in cattle slaughtered in the United States, are of major economic concern to the beef industry. Fusobacterium necrophorum, Trueperella pyogenes, and Salmonella enterica, particularly the serotype Lubbock, are the main etiologic agents. Currently, the control of liver abscesses is based on in-feed use of antibiotics. The emergence and dissemination of antimicrobial resistance to antibiotics use in animals is a public health concern. Plant-based phenolic compounds, called phytophenols, are known to have antimicrobial properties. Our objectives were to evaluate antimicrobial activities of phytophenols on the liver abscess bacterial pathogens. Phytophenols extracted from rosemary, green tea, grapeseed, organic goji berry, and green coffee were selected for testing. The phytophenols were extracted using 75% aqueous acetone and total phenolic content was determined by a spectrophotometric analysis. Bacteria were cultured in Mueller-Hinton broth (S. Lubbock and T. pyogenes) or anaerobic brain-heart infusion broth (F. necrophorum with and without phytophenols, at 6, 12, 24, and 48 hours and bacterial concentrations were determined. If phytophenol was inhibitory, a micro-broth dilution method was used to quantify the inhibition. Phytophenols from green tea, grape seed, and rosemary inhibited T. pyogenes. Further studies are ongoing to investigate different concentrations of phenolic compounds on the pathogens. Phytophenols that inhibit the pathogens may have the potential to be used as feed additives to prevent liver abscesses.

28 In-feed or In-water Antibiotic Administration Did Not Influence the Fecal Prevalence and Antimicrobial Susceptibility Profiles of Salmonella in Piglets

A total of 1,296 weaned piglets were used in a 35-d study to assess the impact of in-feed vs in-water administrations of chlortetracycline (CTC) and or tiamulin on prevalence and antimicrobial resistance (AMR) profiles of Salmonella enterica. Piglets were allocated to 48 pens (27 pigs per pen) and pens were assigned randomly to six treatment groups: control (no antibiotic), in-feed CTC, in-water CTC, in-feed tiamulin, in-water tiamulin, and in feed CTC and tiamulin. Fresh fecal samples were collected randomly from 5 of 27 piglets from each pen on days -7, 0 (pre-treatment), 7, 14 (treatment), 21, and 28 (post-treatment). Salmonella isolation and identification were done by enrichment, plating on selective medium, and species confirmation of putative colonies by PCR. Antimicrobial susceptibility and resistance of the isolates were determined using premade antibiotic panel (SensititreTM CMV3AGNF and BOPO7F) and results were interpreted based on the Clinical and Laboratory Standards Institute guidelines. All Salmonella isolates were identified as serotype Typhimurium. The overall prevalence of Salmonella was 3.0% (43/1,440) with no treatment effect (P > 0.05). All isolates were resistant (100%) to tetracycline and tiamulin. Additionally, the isolates were resistant to ampicillin (100%), streptomycin (100%), sulfisoxazole (100), ciprofloxacin (95.4%) and nalidixic acid (74.4%). Only a few isolates were resistant to trimethoprim/sulphamethoxazole (4.7%), ceftriaxone (7.0%), and ceftiofur (7.0%). PCR assays indicated the presence of tetB gene in all isolates, while 11 (25.6%) and 4 (9.3%) isolates were positive for tetD and tetA genes, respectively. Neither in-feed nor in-water administration of CTC or tiamulin impacted the fecal prevalence and antimicrobial susceptibility of Salmonella in nursery piglets.

29 Live Yeast and Yeast Extracts with and Without Pharmacological Levels of Zinc on Nursery Pig Growth Performance and Fecal Escherichia coli Antimicrobial Resistance

A total of 360 barrows (DNA 200×400; initially 5.6 kg) were used to evaluate yeast-based probiotics (Phileo by Lesaffre, Milwaukee, WI) in diets with or without pharmacological levels of Zn on growth and fecal Escherichia coli antimicrobial resistance (AMR). There were 5 pigs/pen and 18 pens/treatment. Dietary treatments were arranged in a 2×2 factorial with main effects of yeast pre- and probiotics (0 vs. 0.10% Actisaf Sc 47 HR+, 0.05% SafMannan, and 0.05% Nucleosaf in phase 1 then concentrations were lowered by 50% in phase 2) and pharmacological levels of Zn (110 vs. 3,000 mg/kg in phase 1 and 2,000 mg/kg in phase 2 provided by zinc oxide). Treatments were fed in two phases from d 0 to 7 and 7 to 21 with a common diet fed from d 21 to 42 post-weaning. There were no probiotics×Zn interactions. From d 0 to 21, pigs fed pharmacological Zn had increased (P < 0.001) ADG and ADFI; however, there were no effects of added pre- and probiotics. Fecal samples were collected on d 4, 21, and 42 from the same three pigs/pen for AMR profiles and fecal dry matter (DM). On d 4, pigs fed pharmacological Zn had greater fecal DM (P = 0.043); however, no differences were observed on d 21 or 42. E. coli was isolated from fecal samples and species confirmation was accomplished by PCR detection of uidA and clpB genes. Microbroth dilution method using SensititreTM CMV3AGNF panel was used to determine antimicrobial susceptibilities of E. coli isolates to 14 different antimicrobials. There was no evidence for differences in AMR of fecal E. coli isolates to antibiotics by added pre- and probiotics or Zn. Results suggest that pharmacological levels of Zn stimulate intake and growth and improve fecal consistency in the nursery with no statistical response from added pre- and probiotics.

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Whole-genome sequencing analysis of uncommon Shiga toxin-producing Escherichia coli from cattle: Virulence gene profiles, antimicrobial resistance predictions, and identification of novel O-serogroups

Shiga toxin-producing E. coli (STEC) are major foodborne pathogens. While many studies have focused on the "top-7 STEC", little is known for minor serogroups. A total of 284 non-top-7 STEC strains isolated from cattle feces were subjected to whole-genome sequencing (WGS) to determine the serotypes, the presence of virulence genes and antimicrobial resistance (AMR) determinants. Nineteen typeable and three non-typeable serotypes with novel O-antigen loci were identified. Twenty-one AMR genes and point mutations in another six genes that conferred resistance to 10 antimicrobial classes were detected, as well as 46 virulence genes. The distribution of 33 virulence genes and 15 AMR determinants exhibited significant differences among serotypes (p < 0.05). Among all strains, 81.7% (n = 232) and 14.1% (n = 40) carried stx2 and stx1 only, respectively; only 4.2% (n = 12) carried both. Subtypes stx1a, stx1c, stx2a, stx2c, stx2d, and stx2g were identified. Forty-six strains carried eae and stx2a and therefore had the potential cause severe diseases; 47 strains were genetically related to human clinical strains inferred from a pan-genome phylogenetic tree. We were able to demonstrate the utility of WGS as a surveillance tool to characterize the novel serotypes, as well as AMR and virulence profiles of uncommon STEC that could potentially cause human illness.

Influence of Cane Molasses Inclusion to Dairy Cow Diets during the Transition Period on Rumen Epithelial Development

Simple Summary

The rumen epithelium of dairy cattle undergoes a transformation in response to dietary and physiological changes. Rumen papillae development and adaptation from a typical dry cow diet to a lactating diet can require a substantial amount of time, subsequently limiting the amount of volatile fatty acids (VFA) absorbed from the rumen during early lactation. Infusions of butyrate into the rumen of sheep stimulates cellular proliferation of rumen epithelial tissue, which may prove beneficial for ruminal papillae development in dairy cows during the dry period. However, no studies have investigated mechanisms associated with rumen epithelial adaptation in periparturient dairy cattle. Our hypothesis was that supplementation with cane molasses containing 34% sucrose during the prepartum period would stimulate ruminal butyrate production and ultimately promote ruminal papillae development and absorption rate, thus increasing dry matter intake (DMI) and milk production during the postpartum period. Results from these experiments indicate that diets containing cane molasses during a 60 day dry period can positively influence transition cow performance.

Abstract

The objective of this study was to evaluate the addition of cane molasses during a 60 day dry period on performance and metabolism of Holstein cows during prepartum and postpartum periods. For experiment 1, 26 primiparous and 28 multiparous cows were used. Upon freshening, all cows were offered a common lactation diet. For experiment 2, six multiparous cows fitted with rumen cannulas were used to measure performance and metabolism, following the same protocol as experiment 1. Ruminal propionate increased by 10% during both prepartum and postpartum periods; however, papillae area was greater for cows not fed molasses, and volatile fatty acids (VFA) absorption from the rumen was not increased, resulting in similar glucagon-like-peptide-2 receptor (GLP-2R) density. The improved dry matter intake, when molasses was added into prepartum diets, translated into increased milk yield and energy-corrected milk (ECM) in Experiment 1 only for multiparous cows. For experiment 2, the improvement on milk performance was also observed, where cows fed molasses had 18.5% greater ECM production. Feeding molasses during a 60 day dry period positively influenced transition cow performance, and it was not accompanied by changes in rumen morphometrics; however, this indicates enhanced adaptation by the rumen epithelium based on similar capabilities for VFA absorption.

Bacterial community analysis of purulent material from liver abscesses of crossbred cattle and Holstein steers fed finishing diets with or without tylosin

Liver abscesses in feedlot cattle are polymicrobial infections. Culture-based studies have identified Fusobacterium necrophorum as the primary causative agent, but a number of other bacterial species are frequently isolated. The incidence of liver abscesses is highly variable and is affected by a number of factors, including cattle type. Holstein steers raised for beef production have a higher incidence than crossbred feedlot cattle. Tylosin is the commonly used antimicrobial feed additive to reduce the incidence of liver abscesses. The objective of this study was to utilize 16S ribosomal RNA amplicon sequence analyses to analyze the bacterial community composition of purulent material of liver abscesses of crossbred cattle (n = 24) and Holstein steers (n = 24), each fed finishing diet with or without tylosin. DNA was extracted and the V3 and V4 regions of the 16S rRNA gene were amplified, sequenced, and analyzed. The minimum, mean, and maximum sequence reads per sample were 996, 177,070, and 877,770, respectively, across all the liver abscess samples. Sequence analyses identified 5 phyla, 14 families, 98 genera, and 102 amplicon sequence variants (ASV) in the 4 treatment groups. The dominant phyla identified were Fusobacteria (52% of total reads) and Proteobacteria (33%). Of the top 25 genera identified, 17 genera were Gram negative and 8 were Gram positive. The top 3 genera, which accounted for 75% of the total reads, in the order of abundance, were Fusobacterium, Pseudomonas, and Bacteroides. The relative abundance, expressed as percent of total reads, of phyla, family, and genera did not differ (P > 0.05) between the 4 treatment groups. Generic richness and evenness, determined by Shannon-Weiner and Simpson's diversity indices, respectively, did not differ between the groups. The UniFrac distance matrices data revealed no clustering of the ASV indicating variance between the samples within each treatment group. Co-occurrence network analysis at the genus level indicated a strong association of Fusobacterium with 15 other genera, and not all of them have been previously isolated from liver abscesses. In conclusion, the culture-independent method identified the bacterial composition of liver abscesses as predominantly Gram negative and Fusobacterium as the dominant genus, followed by Pseudomonas. The bacterial community composition did not differ between crossbred and Holstein steers fed finishing diets with or without tylosin.

Leukotoxin production by Fusobacterium necrophorum strains in relation to severity of liver abscesses in cattle

Fusobacterium necrophorum, a Gram-negative anaerobe, is the primary etiologic agent of liver abscesses of beef cattle. The bacterium, a member of the microbial community of the rumen, travels to the liver via portal circulation to cause abscesses. The severity of liver abscesses vary from mild with one or two small abscesses to severe with medium to large multiple abscesses. Leukotoxin, a secreted protein, is the critical virulence factor involved in the infection. Our objective was to compare leukotoxin production between strains of F. necrophorum isolated from mild and severe liver abscesses collected from slaughtered cattle. The quantification of leukotoxin was based on assays to measure cytotoxicity and protein antigen concentration. One-hundred strains, 50 from mild and 50 from severe abscesses, were utilized in the study. Cell-free supernatants were prepared from cultures grown in anaerobic broth at 9 and 24 h incubations. The leukotoxic activity was quantified by measuring cytotoxicity based on the release of lactic dehydrogenase from bovine lymphocyte cells, BL3, treated with the culture supernatant. Leukotoxin protein concentration was quantified by a sandwich ELISA assay with a leukotoxin-specific monoclonal antibody as the capture antibody. The leukotoxin activity and concentration were highly variable among the strains within each severity of liver abscesses. Although the leukotoxic activity was unaffected by incubation time, leukotoxin protein concentration was consistently higher at 24 h compared to 9 h incubation. Strains from severe liver abscesses had significantly higher leukotoxic activity and higher protein concentration compared to strains from mild liver abscesses (P < 0.0001) at both 9 and 24 h culture supernatants. Across all strains, the correlation coefficients between leukotoxic activity and leukotoxin concentration at 9 and 24 h were 0.14 (P = 0.17) and 0.47 (P < 0.0001), respectively. In conclusion, strains isolated from severe liver abscesses had significantly higher leukotoxic activities and leukotoxin protein concentrations compared to strains isolated from mild liver abscesses.

Age Dependence of Antimicrobial Resistance Among Fecal Bacteria in Animals: A Scoping Review

Introduction: A phenomenon of decreasing antimicrobial resistance (AMR) among fecal bacteria as food animals age has been noted in multiple field studies. We conducted a scoping review to summarize the extent, range, and nature of research activity and the data for the following question: "does AMR among enteric/fecal bacteria predictably shift as animals get older?". Methods: This review followed a scoping review methodology framework. Pertinent literature published up until November 2018 for all animals (except humans) was retrieved using keyword searches in two online databases, namely, PubMed® and the Web of Science™ Core Collection, without filtering publication date, geographic location, or language. Data were extracted from the included studies, summarized, and plotted. Study quality was also assessed using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) guidelines for all included papers. Results: The publications with detailed relevant data (n = 62) in food animals, poultry, and dogs were identified. These included longitudinal studies (n = 32), cross-sectional studies of different age groups within one food animal production system or small-animal catchment area (n = 16), and experimental or diet trials (n = 14). A decline in host-level prevalence and/or within-host abundance of AMR among fecal bacteria in production beef, dairy cattle, and swine was reported in nearly two-thirds (65%) of the identified studies in different geographic locations from the 1970's to 2018. Mixed results, with AMR abundance among fecal bacteria either increasing or decreasing with age, have been reported in poultry (broiler chicken, layer, and grow-out turkey) and dogs. Conclusions: Quantitative synthesis of the data suggests that the age-dependent AMR phenomenon in cattle and swine is observed irrespective of geographic location and specific production practices. It is unclear whether the phenomenon predates or is related to antimicrobial drug use. However, almost 50% of the identified studies predate recent changes in antimicrobial drug use policy and regulations in food animals in the United States and elsewhere.

Effects of Zinc and Menthol-Based Diets on Co-Selection of Antibiotic Resistance among E. coli and Enterococcus spp. in Beef Cattle

Antibiotic resistance represents a growing crisis in both human and veterinary medicine. We evaluated the use of antibiotic alternatives-heavy metals and essential oils-in beef cattle feeding, and their effects on Gram-negative and Gram-positive bacteria. In this randomized controlled field trial, we measured the impact of supplemental zinc and menthol on antibiotic resistance among commensal enteric bacteria of feeder cattle. Fecal suspensions were plated onto plain- and antibiotic-supplemented MacConkey and m-Enterococcus agar for quantification of total and antibiotic-resistant Escherichia coli and Enterococcus spp., respectively. Temporal effects on overall E. coli growth were significant (p < 0.05), and menthol was associated with decreased growth on tetracycline-supplemented agar. Zinc was associated with significant increases in growth on erythromycin-supplemented m-Enterococcus agar. Cattle fed zinc exhibited significantly higher levels of macrolide resistance among fecal enterococci isolates.

Shiga Toxin-Producing Escherichia coli in Feces of Finisher Pigs: Isolation, Identification, and Public Health Implications of Major and Minor Serogroups†

ABSTRACT

Shiga toxin-producing Escherichia coli (STEC) are major foodborne human pathogens that cause mild to hemorrhagic colitis, which could lead to complications of hemolytic uremic syndrome. Seven serogroups, O26, O45, O103, O111, O121, O145, and O157, account for the majority of the STEC illnesses in the United States. Shiga toxins 1 and 2, encoded by stx1 and stx2, respectively, and intimin, encoded by eae gene, are major virulence factors. Cattle are a major reservoir of STEC, but swine also harbor them in the hindgut and shed STEC in the feces. Our objectives were to use a culture method to isolate and identify major and minor serogroups of STEC in finisher pig feces. Shiga toxin genes were subtyped to assess public health implications of STEC. Fecal samples (n = 598) from finisher pigs, collected from 10 pig flows, were enriched in E. coli broth and tested for stx1, stx2, and eae by a multiplex PCR (mPCR) assay. Samples positive for stx1 or stx2 gene were subjected to culture methods, with or without immunomagnetic separation and plating on selective or nonselective media, for isolation and identification of stx-positive isolates. The culture method yielded a total of 178 isolates belonging to 23 serogroups. The three predominant serogroups were O8, O86, and O121. The 178 STEC strains included 26 strains with stx1a and 152 strains with stx2e subtypes. Strains with stx1a, particularly in association with eae (O26 and O103), have the potential to cause severe human infections. All stx2-positive isolates carried the subtype stx2e, a subtype that causes edema disease in swine, but is rarely involved in human infections. Several strains were also positive for genes that encode for enterotoxins, which are involved in neonatal and postweaning diarrhea in swine. In conclusion, our study showed that healthy finisher pigs harbored and shed several serogroups of E. coli carrying virulence genes involved in neonatal diarrhea, postweaning diarrhea, and edema disease, but prevalence of STEC of public health importance was low.

HIGHLIGHTS

388 Nutrition and the Ruminal Microbiome: Emerging Frontiers from an Old Friend

Rumen, a pregastric anaerobic gut ecosystem, inhabits arguably the most diverse and complex microbial community, with a mutualistic relationship with the host. The relationship is best exemplified in the utilization of lignocellulosic material and non-protein nitrogen to provide energy and protein to the host. The microbial community of the rumen is composed of bacteria, archaea, protozoa, fungi and bacteriophages. Culture- or microscopy-based procedures have identified over 200 species of bacteria, methanogens, ciliated protozoa and zoosporic fungi. The community analysis based on the genetic material of all microbial cells, called microbiome, has vastly expanded our understanding of the ruminal ecosystem. Microbiome analysis is based on sequencing of the targeted amplicons (16S rDNA variable regions for bacteria and archaea, 18S rDNA for protozoa or Internal Transcribed Regions for fungi) or whole genome shotgun metagenomics analysis. Rapid advancements in nucleic acid sequencing technologies and bioinformatics pipelines have provided unprecedented opportunities to delineate the diversity and complexity of the microbial community in relation ruminal function and dysfunctions and link ruminal microbes to host nutrition and productivity. Culture-independent methods have identified thousands of microbial species in the rumen, suggesting that a major fraction of the microbiome has not been cultured and functionally identified. A core microbiome in bacterial and archaeal populations of the rumen has been identified across a wide geographical regions, but significant variations in diversity, abundance, and individual taxa do exist because of diet and host genetics. However, there is evidence of signature microbiome among individual animals on the same diet and environment. Microbiome-wide association studies in relation to dietary changes, ruminal function and dysfunctions have begun to link and define the complexity of the host-microbe relationships. Translation of the potential of the microbiome analysis is supported by emerging evidences that specific microbiota can be linked to ruminal activity and productivity.

265 Evaluating the route of antibiotic administration and its effect on nursery pig growth performance

A total of 2,592 pigs (L337×1050, PIC, Hendersonville, TN; initially 5.58 kg BW) were used in a 28-d study to evaluate the route of antibiotic administration (in-feed vs in-water) on pig performance. Pigs were weaned at 21 d of age and placed in a commercial research facility with 27 pigs per pen. After a 7-d pre-trial period, pens of pigs were assigned to weight blocks in a randomized complete block design. There were 12 replications per treatment with pen as experimental unit for in-feed medication treatments and a pairs of pens as the experimental unit for water medication treatments. Treatments included a control (no medication), chlortetracycline (CTC) provided via feed or water to achieve 22 mg/kg BW, tiamulin in feed (5 to10 mg/kg BW) or water (23 mg/kg BW), or a combination of CTC and tiamulin in feed. Experimental treatments were provided for 14-d followed by a 14-d period without medication. Data were analyzed using R Studio (Version 3.5.2). From d 0 to 14, there was an antibiotic×route of administration interaction for ADG and G:F. For ADG, pigs fed diets containing CTC had increased (P&lt; 0.05) ADG compared with those fed tiamulin in feed, with pigs provided CTC or tiamulin in the water intermediate. For G:F, pigs provided tiamulin in feed had decreased G:F compared to pigs fed CTC in feed or CTC or tiamulin supplied in water. Pigs fed CTC in the diet had increased ADFI compared to the control with pigs provided antibiotics in the water or tiamulin in feed intermediate (P&lt; 0.05). Pigs provided the combination of CTC and tiamulin in feed were not different than those provided CTC in feed. There was no evidence of difference among treatments in subsequent performance. In summary, providing CTC in feed with or without tiamulin improved nursery pig growth performance.

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18 Impact of in-feed vs. in-water antibiotic administrations on the fecal prevalence and antimicrobial susceptibilities of Campylobacter and Salmonella in piglets

Campylobacter and Salmonella are common food borne pathogens in the gut of pigs and are shed in the feces. The control of these bacteria in pigs is of importance in reducing the potential for transmission to humans. In swine, oral route, either in-feed or in-water, is by far the most common route of administration of antibiotics. Because the distribution of the antibiotic in the gut and the dosage are different, the impact of in-feed vs. in-water administration of antibiotics on the fecal shedding of food borne pathogens, Campylobacter and Salmonella, and on the development of antimicrobial resistance (AMR) in gut bacteria is a largely unexplored area. Therefore, a study was conducted to compare the effects of in-feed and in-water antibiotic administration on fecal prevalence of Campylobacter and Salmonella and AMR development in nursery piglets. A total of 1,296 weaned piglets were allocated into pens (48 pens; 27 pigs per pen) distributed in a single room. Pens were assigned randomly to six treatment groups; Control (No antibiotic), In-feed chlortetracycline (CTC), In-water CTC, In-feed tiamulin, In-water tiamulin, and a combination of CTC and tiamulin (In-feed). Fresh fecal samples were collected randomly from 5 of 27 piglets from each pen on pre-treatment (days -7, 0), treatment (days 7, 14) and post-treatment (days 21, 28) phases. Bacterial isolations and identifications were done by culture method and PCR, respectively. Overall prevalence of Campylobacter and Salmonella were 18.2% (262/1,440) and 3.9% (56/1,440) respectively. Speciation of Campylobacter isolates indicated C. hyointestinalis (17.9%; 258/1,440) and C. coli (0.3%; 4/1,440). Pigs from control group had a higher prevalence (P&lt; 0.05) of both Campylobacter and Salmonella when compared to other treatment groups. Both treatment and post-treatment phases had a significant effect on the prevalence of Campylobacter and Salmonella (P&lt; 0.05).

Population structure of Salmonella enterica serotype Mbandaka reveals similar virulence potential irrespective of source and phylogenomic stratification

Background: Salmonella enterica serotype Mbandaka ( Salmonella ser. Mbandaka) is a multi-host adapted Non-typhoidal Salmonella (NTS) that can cause foodborne illnesses in human. Outbreaks of Salmonella ser. Mbandaka contributed to the economic stress caused by NTS due to hospitalizations. Whole genome sequencing (WGS)-based phylogenomic analysis facilitates better understanding of the genomic features that may expedite the foodborne spread of Salmonella ser. Mbandaka. Methods: In the present study, we define the population structure, antimicrobial resistance (AMR), and virulence profile of Salmonella ser. Mbandaka using WGS data of more than 400 isolates collected from different parts of the world. We validated the genotypic prediction of AMR and virulence phenotypically using an available set of representative isolates. Results: Phylogenetic analysis of Salmonella ser. Mbandaka using Bayesian approaches revealed clustering of the population into two major groups; however, clustering of these groups and their subgroups showed no pattern based on the host or geographical origin. Instead, we found a uniform virulence gene repertoire in all isolates. Phenotypic analysis on a representative set of isolates showed a similar trend in cell invasion behavior and adaptation to a low pH environment. Both genotypic and phenotypic analysis revealed the carriage of multidrug resistance (MDR) genes in Salmonella ser. Mbandaka. Conclusions: Overall, our results show that the presence of multidrug resistance along with adaptation to broad range of hosts and uniformity in the virulence potential, isolates of Salmonella ser. Mbandaka from any source could have the potential to cause foodborne outbreaks as well as AMR dissemination.

Effectiveness of a Direct-Fed Microbial Product Containing Lactobacillus acidophilus and Lactobacillus casei in Reducing Fecal Shedding of Escherichia coli O157:H7 in Commercial Feedlot Cattle

The objective of this study was to evaluate the effectiveness of a direct-fed microbial (DFM) product in reducing fecal shedding of Escherichia coli O157:H7 in finishing commercial feedlot cattle in Kansas (KS) and Nebraska (NE). Utilizing a randomized complete block design within the feedlot (KS, n = 1; NE, n = 1), cattle were randomly allocated to 20 pens, grouped in blocks of two based on allocation date, and then, within the block, randomly assigned to a treatment group (DFM or negative control). The DFM product was included in the diet at a targeted daily dose of 1 × 10⁹ colony-forming units (CFU) of the Lactobacillus acidophilus and Lactobacillus casei combination per animal for at least 60 d before sampling. Feedlots were sampled for four consecutive weeks; weekly sampling consisted of collecting 20 pen floor fecal samples per pen. Fecal samples were subjected to culture-based methods for detection and isolation of E. coli O157, and positive samples were quantified using real-time polymerase chain reaction. Primary outcomes of interest were fecal prevalence of E. coli O157:H7 and E. coli O157 supershedding (≥10⁴ CFU/g of feces) prevalence. Data for each feedlot were analyzed at the pen level using mixed models accounting for the study design features. Model-adjusted mean E. coli O157:H7 fecal prevalence estimates (standard error of the mean [SEM]) for DFM and control groups were 8.2% (SEM = 2.2%) and 9.9% (SEM = 2.5%) in KS and 14.6% (SEM = 2.8%) versus 14.3% (SEM = 2.6%) in NE; prevalence did not differ significantly between treatment groups at either site (KS, p = 0.51; NE, p = 0.92). Mean E. coli O157 supershedding prevalence estimates for DFM and control groups were 2.2% (SEM = 0.7%) versus 1.8% (SEM = 0.7%) in KS (p = 0.66) and 6.7% (SEM = 1.5%) versus 3.2% (SEM = 1.0%) in NE (p = 0.04). In conclusion, administering the DFM product in the finishing diet of feedlot cattle did not significantly reduce E. coli O157:H7 fecal prevalence or supershedding prevalence in study pens at either commercial feedlot.

Polymerase Chain Reaction-Based Prevalence of Serogroups of Escherichia coli Known to Carry Shiga Toxin Genes in Feces of Finisher Pigs

Shiga toxin-producing Escherichia coli (STEC) are major foodborne pathogens and seven serogroups, O26, O45, O103, O111, O121, O145, and O157, that account for the majority of the STEC-associated illness in humans. Similar to cattle, swine also harbor STEC and shed them in the feces and can be a source of human STEC infections. Information on the prevalence of STEC in swine feces is limited. Therefore, our objective was to utilize polymerase chain reaction (PCR) assays to determine prevalence of major virulence genes and serogroups of STEC. Fecal samples (n = 598), collected from finisher pigs within 3 weeks before marketing in 10 pig flows located in 8 states, were included in the study. Samples enriched in E. coli broth were subjected to a real-time PCR assay targeting three virulence genes, Shiga toxin 1 (stx1), Shiga toxin 2 (stx2), and intimin (eae), which encode for Shiga toxins 1 and 2, and intimin, respectively. A novel PCR assay was designed and validated to detect serogroups, O8, O20, O59, O86, O91, O100, O120, and O174, previously reported to be commonly present in swine feces. In addition, enriched fecal samples positive for Shiga toxin genes were subjected to a multiplex PCR assay targeting O26, O45, O103, O104, O111, O121, O145, and O157 serogroups implicated in human clinical infections. Of the 598 fecal samples tested by real-time PCR, 25.9%, 65.1%, and 67% were positive for stx1, stx2, and eae, respectively. The novel eight-plex PCR assay indicated the predominant prevalence of O8 (88.6%), O86 (35.5%), O174 (24.1%), O100 (20.2%), and O91 (15.6%) serogroups. Among the seven serogroups relevant to human infections, three serogroups, O121 (17.6%), O157 (14%), and O26 (11%) were predominant. PCR-based detection indicated high prevalence of Shiga toxin genes and serogroups that are known to carry Shiga toxin genes, including serogroups commonly prevalent in cattle feces and implicated in human infections and in edema disease in swine.

Multiplex PCR Assays for the Detection of One Hundred and Thirty Seven Serogroups of Shiga Toxin-Producing Escherichia coli Associated With Cattle

Escherichia coli carrying prophage with genes that encode for Shiga toxins are categorized as Shiga toxin-producing E. coli (STEC) pathotype. Illnesses caused by STEC in humans, which are often foodborne, range from mild to bloody diarrhea with life-threatening complications of renal failure and hemolytic uremic syndrome and even death, particularly in children. As many as 158 of the total 187 serogroups of E. coli are known to carry Shiga toxin genes, which makes STEC a major pathotype of E. coli. Seven STEC serogroups, called top-7, which include O26, O45, O103, O111, O121, O145, and O157, are responsible for the majority of the STEC-associated human illnesses. The STEC serogroups, other than the top-7, called “non-top-7” have also been associated with human illnesses, more often as sporadic infections. Ruminants, particularly cattle, are principal reservoirs of STEC and harbor the organisms in the hindgut and shed in the feces, which serves as a major source of food and water contaminations. A number of studies have reported on the fecal prevalence of top-7 STEC in cattle feces. However, there is paucity of data on the prevalence of non-top-7 STEC serogroups in cattle feces, generally because of lack of validated detection methods. The objective of our study was to develop and validate 14 sets of multiplex PCR (mPCR) assays targeting serogroup-specific genes to detect 137 non-top-7 STEC serogroups previously reported to be present in cattle feces. Each assay included 7–12 serogroups and primers were designed to amplify the target genes with distinct amplicon sizes for each serogroup that can be readily identified within each assay. The assays were validated with 460 strains of known serogroups. The multiplex PCR assays designed in our study can be readily adapted by most laboratories for rapid identification of strains belonging to the non-top-7 STEC serogroups associated with cattle.

Potential risk-factors affecting Salmonella sp. and Escherichia coli occurrence and distribution in Midwestern United States swine feed mills

AIM

This study aimed to evaluate the patterns and potential risk factors associated with the occurrence of Salmonella sp. and Escherichia coli in selected United States swine feed mills.

METHODS AND RESULTS

A total of 405 samples were collected during fall 2018, spring and summer 2019 from selected sites including floors, equipment, shoes and feed in six feed mills in the US Midwest region. Each sample was analysed for the presence of Salmonella and E. coli with culture methods and confirmed by PCR. A survey regarding production volumes, hygiene practices and microbial testing capabilities was conducted in each facility All mills had at least one sampling site positive for either Salmonella or E. coli. Of the 405 samples, 4·7, and 14·1% were positive for Salmonella sp., and E. coli respectively. Sites with higher percentages of positive samples were the receiving, manufacturing, and control area floors. The survey responses indicated that the age of the mill might be a risk factor for bacterial contamination: the older the facility, the higher the number of positive samples. Other risk factors evaluated, such as the production capacity, did not appear to relate to bacterial prevalence.

CONCLUSION

The data documents the presence of E. coli and Salmonella in selected US swine feed mills, and an association between E. coli occurrence and number of ingredient suppliers to feed mill.

SIGNIFICANCE AND IMPACT OF THE STUDY

This information could be used to understand risk factors affecting the occurrence of Salmonella sp. and E. coli in feed mills and help implement monitoring and mitigation strategies for public health.

Associations Between Season, Processing Plant, and Hide Cleanliness Scores with Prevalence and Concentration of Major Shiga Toxin-Producing Escherichia coli on Beef Cattle Hides

The objectives of this study were (1) to estimate the prevalence and concentration of the seven major Shiga toxin-producing Escherichia coli (STEC) serogroups (O26, O45, O103, O111, O121, O145, and O157), collectively called STEC-7, on cattle hides collected in different seasons and beef processing plants; and (2) to determine associations of season, plant, and hide cleanliness scores with the prevalence and concentration of STEC-7. A total of 720 hide surface samples (240/season) were collected over three seasons (summer and fall 2015 and spring 2016) from beef cattle carcasses in four commercial processing plants in the United States. Samples were subjected to selective culture and spiral plating methods. Overall model-adjusted mean prevalence (95% confidence interval) was 0.3% (0.03-2.3%) for STEC O26; 0.05% (<0.01-8.5%) for STEC O45; 0.2% (0.02-1.9%) for STEC O103; 0.05% (<0.01-8.5%) for STEC O145; and 3.1% (0.6-15.2%) for STEC O157. Four percent of hide samples were enumerable for STEC O157; mean concentration (standard deviation) = 2.1 (0.7) log₁₀ colony-forming units (CFUs)/100 cm². No samples were enumerable for non-O157 STEC. Hide-on prevalence of STEC O157 and STEC non-O157 (specifically of STEC O103) was higher in summer and spring, respectively. Across seasons and plants, the most common STEC non-O157 serogroups in this study (O26 and O103) were associated with a higher prevalence of STEC O157. Season and plant played a role in prevalence and concentration of STEC in beef cattle hides, varying by serogroup. Tailoring mitigation strategies at the plant can be challenging and processors would benefit from supplementary preharvest interventions to reduce overall contamination pressure at the plant, especially in fall and spring months when hide-on prevalence of STEC non-O157 is higher.

Impact of added copper, alone or in combination with chlortetracycline, on growth performance and antimicrobial resistance of fecal enterococci of weaned piglets

Studies suggest a link between added copper (Cu) and co-selection of antimicrobial resistance (AMR) in Enterococcus spp., but data are inconsistent. This study aimed to assess the impact of added Cu, alone or with a feed-grade antimicrobial, on growth performance, transferable Cu resistance gene (tcrB) prevalence, abundance of tcrB in fecal community DNA, and AMR in fecal enterococci in weaned piglets. A total of 320 barrows (DNA 200 × 400, DNA Genetics) weaned at approximately 21 d of age with 7.4 kg (7.4 ± 0.06 kg) BW were used in a 28-d study. Piglets were fed a common non-medicated diet for 7 d of acclimation. Treatments were arranged in a 2 × 2 factorial design with main effects of added Cu (0 vs. 200 mg/kg Cu from Cu sulfate) and chlortetracycline (0 vs. 440 mg/kg CTC). Growth performance and fecal samples were obtained on days 0, 14, and 28. There was no evidence (P > 0.05) for Cu and CTC interaction in growth performance. Pigs fed diets with added Cu had increased (P < 0.05) ADG and ADFI from days 0 to 14, with no evidence for differences (P > 0.05) from days 15 to 28 and 0 to 28. Pigs fed diets with CTC had improved (P < 0.01) ADG, ADFI, and G:F from days 0 to 28. Prevalence of tcrB-positive enterococci was not affected by the addition of Cu and/or CTC (P > 0.05). Prevalence of tcrB-positive enterococci was higher on day 14 than other sampling days (P = 0.002). Prevalence of tetracycline resistance gene [tet(M)]-positive enterococci was not affected by treatments or day (P > 0.05). Prevalence of macrolide resistance gene [erm(B)]-positive enterococci had a significant treatment and sampling day interaction (P = 0.021). The abundance of the tcrB gene in feces, quantified by PCR, was not affected by Cu treatment. The median Cu minimum inhibitory concentrations (MIC) of tcrB-negative and -positive isolates were 3 and 20 mM, respectively (P < 0.001). For day 0 and day 28, all Enterococcus isolates were susceptible to gentamicin, kanamycin, streptomycin, daptomycin, and tigecycline, with a majority of isolates resistant to chloramphenicol, erythromycin, lincomycin, linezolid, tetracycline, tylosin tartrate, and Synercid. In conclusion, 200 mg/kg added Cu or 440 mg/kg CTC in nursery diets improved growth performance of nursery pigs. Added Cu, with or without a selection pressure of CTC, did not increase Cu-resistant enterococci and did not co-select resistance to antibiotics.

449 Late-Breaking: Impact of feeding a propriety yeast-based synbiotic product on fecal shedding of top-7 Shiga toxin-producing Escherichia coli in feedlot cattle

Shiga toxin-producing E. coli (STEC) belonging to serogroups O26, O45, O111, O103, O121, O145, and O157, called ‘top-7’, are major foodborne pathogens. Cattle are a major reservoir, in which STEC colonize the hindgut and are shed in the feces, which is a major source of contamination of food. Our objective was to evaluate the impact of a proprietary yeast-based synbiotic product (prebiotic and probiotic; Alltech, Inc., Nicholasville, KY) on fecal shedding of top-7 STEC in feedlot cattle. Twenty existing pens, housing 40–112 steers per pen, with an estimated 60 to 90 days to slaughter, were randomly assigned to a control group or a treatment group that received 22 g of the synbiotic product per steer per day, as a top dress, in a finishing diet. Twenty pen-floor fecal samples were collected from each pen on days 0, 21, 42, and 54. Fecal samples were enriched and subjected to a multiplex PCR assay targeting serogroup-specific genes for the top-7 STEC and three major virulence genes, stx1 (Shiga toxin 1), stx2 (Shiga toxin 2), and eae (intimin). Bivariate descriptive statistics for the major serogroups and virulence genes were assessed prior to multivariable analysis using mixed effects logistic regression. The overall prevalence of the top-7 serogroups were 44.5% of O26, 41.3% of O157, 15.1% of O103, 13.7% of O45, 7.8% of O121, and 0.6% of O111. The overall prevalence of stx1, stx2, and eae were 43.9%, 70.8%, and 49%, respectively. E. coli O26, O157, and O45 had a significant treatment and sampling day interaction (P &lt; 0.0001). On d 42, fecal samples from treated group had lower prevalence (P &lt; 0.01) of O26, O103, and O45 compared to the control group. In conclusion, the in-feed administration of the synbiotic product appears to reduce fecal shedding of certain top-7 STEC serogroups in the feedlot cattle.

Quantification of Bacteria Indicative of Fecal and Environmental Contamination from Hides to Carcasses

Fecal bacteria, which reside in the gastrointestinal tract of cattle, can contaminate beef carcasses during processing. In beef cattle slaughter plants, the presence and concentrations of generic Escherichia coli, coliforms, Enterobacteriaceae (EB), and total aerobic bacteria are monitored as indicator organisms of fecal and environmental contamination. The objectives of this study were as follows: (1) to determine the concentrations of generic E. coli, coliforms, EB, and aerobic bacteria on beef carcasses at different processing points in Midwestern commercial beef slaughter plants during the summer, spring, and fall seasons; and (2) to estimate bacterial transfer on carcasses during the hide removal and evisceration processes. Hide and carcass surface sample swabs were collected from slaughtered cattle at four large commercial processing plants. At each plant visit (3 visits to each of the 4 plants) and during 3 seasons, 20 samples were collected at 5 points: hide-on (hide of animal near exsanguination pit), hide-off carcass, pre-evisceration carcass, postevisceration carcass, and postintervention carcass, for a total of 3600 samples. Bacterial concentrations were determined using 3M^™ Petrifilm^™ plates. Associations between season and processing plant with concentrations of E. coli, coliforms, EB, and total aerobic bacteria, overall, between hide-on and hide-off, and between pre- and post-evisceration, were evaluated using multilevel mixed-effects linear regression models. Bacterial concentrations on beef carcasses significantly decreased throughout processing. Moreover, hide removal was an important source of carcass contamination, given bacterial concentrations detected on hide-off carcass samples were the highest, and bearing in mind that carcass muscle surfaces should be sterile. Results from this study indicate that the interventions applied by the processing plants were effective, as they probably contributed to the significant reduction of bacterial concentrations of carcasses.