The Use of Direct-Fed Microbials to Reduce Shedding ofEscherichia coliO157 in Beef Cattle: A Systematic Review and Meta-analysis

Investigation of Feedlot-level Use of a Direct-fed Microbial on Fecal Shedding of E. coli O157:H7

Our objectives were to determine whether the feedlot-level use of a direct-fed microbial (DFM; Lactobacillus animalis LA51 and Propionibacterium freudenreichii PF24; Bovamine Defend®, 2 × 109 CFU/g) was associated with fecal prevalence and concentration of E. coli O157:H7, and determine pen- and feedlot-level risk factors associated with fecal E. coli O157:H7 prevalence in cattle pens from commercial feedlot operations. Twenty commercial feedlots in Nebraska, ten that included DFM (DFM) and ten that did not (no-DFM), were sampled during the summer of 2017. In each sampling month, 22 pen-floor fecal samples were collected from three pens in each feedlot. Samples were subjected to cultural and molecular procedures for the detection of E. coli O157:H7 (immunomagnetic separation, plating on selective media, followed by PCR confirmation) and spiral plating for quantification. A total of 1,320 samples from 180 pens of finishing cattle belonging to 20 feedlots, which were sampled three times throughout a 12-week period, were processed and tested. Across all feedlots and sampling months, the mean within-pen prevalence was 13.5% (95% CI = 2.6-47.4%). The association between DFM status and the within-pen prevalence of E. coli O157:H7 depended significantly (p < 0.05) on the sampling month. The second sampling month between late July and mid-August corresponded to the highest within-pen prevalence estimates reported in this study, with no-DFM pens having a higher prevalence than DFM pens. After accounting for the DFM status, and based on multivariable analyses, sampling month, average pen body weight, and weather conditions were significantly associated with the within-pen fecal prevalence of E. coli O157:H7. Collectively, these findings demonstrate that the use of a DFM containing Lactobacillus animalis LA51 and Propionibacterium freudenreichii PF26 in feedlots showed potential in reducing fecal E. coli O157:H7 prevalence in cattle during times when prevalence peaks.

Differential Age-Based Response Induced by a Commercial Probiotic Supplementation in Pastured Goats

The potential benefit of probiotics in small ruminant production systems has largely been unexplored. We evaluated the effect of a goat commercial probiotic on health and performance indicators in pastured goats from birth until 10 months. We randomly allocated 26 newborn nursing goat kids to two groups: a control group that received saline and a treatment group that received a commercial probiotic paste orally. We evaluated select observable health indicators (inappetence, diarrhea, coughing), weight, immunity (IgA, IgG, and innate immune response), total protein, hematocrit (HCT), total lactic acid bacteria (LAB), total coliforms, and prevalence of Escherichia coli (E. coli) primary virulence genes (stx1, stx2, and eae) during the experimental period. The results revealed no significant differences in the health indicators, LAB count, and total E. coli count. Prevalence of stx1 at 1 week of age and both stx1 and stx2 genes 4 months post-weaning was significantly (P < 0.05) higher in probiotic-supplemented goats. Probiotic supplementation significantly (P < 0.05) increased the total protein and IgA 1 month post-supplementation during the pre-weaning period and innate immune markers 2 days post-weaning. The HCT in probiotic-supplemented goats was significantly (P < 0.05) higher at 1 and 2 months post-weaning. The growth rate was not affected by probiotic supplementation in pre- and peri-weaned goats but was significantly (P < 0.05) lowered in goats older than 4 months in the supplemented group. In this pastured goat production study, there were mixed responses to a commercial probiotic in healthy goats based on age. The study suggests that early daily probiotic supplementation in pre-weaned pastured goats may have immune stimulation benefits, but in older healthy animals, post-weaning net benefits are unclear and further research is recommended.

Antimicrobial and Mycotoxin Reducing Properties of Lactic Acid Bacteria and Their Influence on Blood and Feces Parameters of Newborn Calves

The aim of this study was to evaluate the influence of in acid whey (AW) multiplied Lactiplantibacillus plantarum LUHS135 (L.pl135), Lacticaseibacillus paracasei LUHS244 (L.pc244), and their biomass combination on newborn calves' feces and blood parameters. Additionally, the antimicrobial and mycotoxin-reducing properties and the resistance to antibiotics of the tested lactic acid bacteria (LAB) strains were analyzed. In order to ensure effective biomass growth in AW, technological parameters for the supplement preparation were selected. Control calves were fed with a standard milk replacer (SMR) and treated groups (from the 2nd day of life until the 14th day) were supplemented with 50 mL of AWL.pl135, AWL.pc244, and AWL.pl135×L.pc244 (25 mL AWL.pl135 + 25 mL AWL.pc244) in addition to SMR. It was established that L.pl135 and L.pc244 possess broad antimicrobial activities, are non-resistant to the tested antibiotics, and reduce mycotoxin concentrations in vitro. The optimal duration established for biomass growth was 48 h (LAB count higher than 7.00 log10 CFU mL-1 was found after 48 h of AW fermentation). It was established that additional feeding of newborn calves with AWL.pl135, AWL.pc244, and AWL.pl135×L.pc244 increased lactobacilli (on average by 7.4%), and AWL.pl135 and AWL.pc244 reduced the numbers of Enterobacteriaceae in calves' feces. The tested supplements also reduced the lactate concentration (on average, by 42.5%) in calves' blood. Finally, the tested supplements had a positive influence on certain health parameters of newborn calves; however, further research is needed to validate the mechanisms of the beneficial effects.

Impact of the Probiotic Organism Megasphaera elsdenii on Escherichia coli O157:H7 Prevalence in Finishing Cattle

Feedlot cattle commonly shed the foodborne pathogen Escherichia coli O157:H7 in their feces. Megasphaera elsdenii (ME), a lactic acid-utilizing bacterium, is commonly administered to cattle to avoid lactate accumulation in the rumen and to control ruminal acidosis. The impact of administering ME on foodborne pathogen prevalence, specifically E. coli O157:H7, has not been explored. The purpose of this study was to quantify E. coli O157:H7 prevalence in finishing cattle administered ME. Cattle (n = 448) were assigned to treatments in a randomized complete block design with repeated measurements over two sampling periods. Treatments were arranged as a 2 × 2 factorial containing: ruminally protected lysine (RPL; included for a complementary study) fed at 0% or 0.45% of diet dry matter; with or without ME. Freeze-dried ME was administered as an oral drench (1 × 1010 CFU/steer on day one) and then top dressed onto basal diets (1 × 107 CFU/steer) daily thereafter. Rectoanal mucosal swabs (RAMS) were obtained from animals before harvest to determine the E. coli O157:H7 prevalence. The inclusion of RPL (P = 0.2136) and ME (P = 0.5012) did not impact E. coli O157:H7 prevalence, and RPL was not included in any significant interactions (P > 0.05). A significant interaction was observed between ME and sampling period (P = 0.0323), indicating that the effect of ME on E. coli O157:H7 prevalence varied over the sampling period. A diet containing ME reduced the odds of E. coli O157:H7 prevalence by 50% during sampling period 1 (8.0% and 14.7% for cattle with and without ME, respectively) and increased the odds by 23% during sampling period 2 (10.8% and 8.9% for cattle with and without ME, respectively). Administering ME in cattle diets did not impact E. coli O157:H7 in feedlot cattle. This is the first study to investigate the use of ME as a preharvest food safety intervention in cattle, and additional research is necessary to determine the efficacy.

Effect of probiotic lactobacilli supplementation on growth parameters, blood profile, productive performance, and fecal microbiology in feedlot cattle

Lactic acid bacteria (LAB) selected on the basis of probiotic characteristics were administered to beef feedlot catlle and the effect on body condition/growth and nutritional-metabolic status as well as on E. coli O157:H7 fecal shedding, were investigated. A feeding trials involving 126 steers were used to evaluate the effects of Lactobacillus acidophilus CRL2074, Limosilactobacillus fermentum CRL2085 and Limosilactobacillus mucosae CRL2069 and their combinations (5 different probiotic groups and control) when 10⁷-10⁸ CFU/animal of each probiotic group were in-feed supplemented. Cattle were fed a high energy corn-based diet (16 to 88%) and samples from each animal were taken at 0, 40, 104 and 163 days. In general, animals body condition and sensorium state showed optimal muscle-skeletal development and behavioral adaption to confinement; no nasal/eye discharges and diarrheic feces were observed. The nutritional performance of the steers revealed a steady increase of biometric parameters and weight. Animals supplied with L. mucosae CRL2069 for 104 days reached the maximum mean live weight (343.2 kg), whereas the greatest weight daily gain (1.27 ± 0.16 Kg/day) was obtained when CRL2069 and its combination with L. fermentum CRL2085 (1.26 ± 0.11 kg/day) were administered during the complete fattening cycle. With several exceptions, bovine cattle blood and serum parameters showed values within referential ranges. As a preharvest strategy to reduce Escherichia coli O157:H7 in cattle feces, CRL2085 administered during 40 days decreased pathogen shedding with a reduction of 43% during the feeding period. L. fermentum CRL2085 and L. mucosae CRL2069 show promise for feedlot cattle feeding supplementation to improve metabolic-nutritional status, overall productive performance and to reduce E. coli O157:H7 shedding, thus decreasing contamination chances of meat food products.

Effects of a novel direct-fed microbial on growth performance, carcass characteristics, nutrient digestibility, and ruminal morphology of beef feedlot steers

The effects of a novel direct-fed microbial (DFM) on feedlot performance, carcass characteristics, digestibility, ruminal morphology, and volatile fatty acid (VFA) profile of finishing steers were evaluated. Single-source Angus-crossbred yearling steers (n = 144; initial body weight (BW) = 371 ± 19 kg) were used in a randomized complete block design. Steers were blocked by initial BW and randomly assigned to treatments (12 pens/treatment; 4 steers/pen). Treatments included (A) CONTROL (no DFM, tylosin, or monensin, (B) MONTY (monensin sodium [330 mg/animal-daily] and tylosin phosphate [90 mg/animal-daily]), and (C) MONPRO (monensin sodium [same as previous] and Lactobacillus salivarius L28 [1 × 106 CFU/animal-daily]). Treatments were included in a steam-flaked corn-based finisher diet offered once daily using a clean-bunk management for ~149 d. The digestibility assessment was performed from days 70 to 74. Ruminal fluid and rumen tissue samples were collected at the slaughter for VFA profile and papillae morphology analyses, respectively. Data were analyzed using the GLIMMIX procedure of SAS with pen serving as the experimental unit, treatment as fixed effect, and BW block as random effect. Steers offered MONPRO had on average 5.3% less (P < 0.01) dry matter intake (9.56 kg/d) compared with either CONTROL (10.16 kg/d) or MONTY (9.96 kg/d). The carcass-adjusted final BW (613 kg; P = 0.23), overall average daily gain (1.64 kg/d; P = 0.23), and gain-efficiency (0.165; P = 0.61) were not affected by treatments. Steers offered CONTROL had greater (P < 0.01) marbling score and tended (P = 0.06) to have less carcasses grading Select and tended (P = 0.10) to have more carcasses grading Upper-Choice, while other carcass characteristics and liver-abscesses were not affected (P ≥ 0.23) by treatments. The digestibility of nutrients (P ≥ 0.13) and the ruminal VFA profile (P ≥ 0.12) were not affected by treatments. Steers offered MONPRO tended (P = 0.09) to have 16% greater average papillae number compared to other treatments. Yearlings offered finishing diets containing L. salivarius L28 plus monensin did not affect growth performance, digestibility, or ruminal VFA, but reduced feed intake. Carcass quality was negatively affected by treatments, while animals consuming L. salivarius L28 and monensin tended to improve ruminal morphology. Current findings in ruminal morphology and feed intake may warrant further assessment of diets containing L. salivarius L28 on beef cattle food safety aspects.

Reduction of Pathogens in Feces and Lymph Nodes Collected from Beef Cattle Fed Lactobacillus salivarius (L28), Lactobacillus acidophilus (NP51) and Propionibacterium freudenreichii (NP28), Commercially Available Direct-Fed Microbials

The purpose of the study was to evaluate the prevalence and concentration of foodborne pathogens in the feces and peripheral lymph nodes (PLNs) of beef cattle when supplemented with direct-fed microbials (DFMs) in feedlots. Fecal samples were collected from the pen floors over a 5-month period at three different feedlots in a similar geographical location in Nebraska, where each feed yard represented a treatment group: (i.) control: no supplement, (ii.) Bovamine Defend: supplemented with NP51 and NP24 at a target dose of 9 log₁₀CFU/g/head/day, and (iii.) Probicon: supplemented with L28 at a target dose of 6 log₁₀CFU/g/head/day. Each fecal sample was tested for the prevalence of E. coli O157:H7 and Salmonella, and concentration of E. coli O157:H7, Enterobacteriaceae and Clostridium perfringens. Cattle were harvested and PLNs were collected on the harvest floor. Real-time Salmonella PCR assays were performed for each PLN sample to determine Salmonella presence. The cattle supplemented with both DFMs had reduced foodborne pathogens in fecal samples, but feces collected from the pens housing the cattle supplemented with Probicon consistently had significantly less E. coli O157:H7 and Salmonella prevalence as well as a lower C. perfringens concentration. While DFMs do not eliminate foodborne pathogens in fecal shedding and PLNs, the use of DFMs as a pre-harvest intervention allows for an effective way to target multiple pathogens reducing the public health risks and environmental dissemination from cattle.

Super Shedding in Enteric Pathogens: A Review

Super shedding occurs when a small number of individuals from a given host population shed high levels of a pathogen. Beyond this general definition, various interpretations of the shedding patterns have been proposed to identify super shedders, leading to the description of the super shedding phenomenon in a wide range of pathogens, in particular enteric pathogens, which are of considerable interest. Several underlying mechanisms may explain this observation, including factors related to the environment, the gut microbiota, the pathogen itself (i.e., genetic polymorphism), and the host (including immune factors). Moreover, data suggest that the interplay of these parameters, in particular at the host-pathogen-gut microbiota interface, is of crucial importance for the determination of the super shedding phenotype in enteric pathogens. As a phenomenon playing an important role in the epidemics of enteric diseases, the evidence of super shedding has highlighted the need to develop various control strategies.

Administration of probiotic lactic acid bacteria to modulate fecal microbiome in feedlot cattle

Modulation of animal gut microbiota is a prominent function of probiotics to improve the health and performance of livestock. In this study, a large-scale survey to evaluate the effect of lactic acid bacteria probiotics on shaping the fecal bacterial community structure of feedlot cattle during three experimental periods of the fattening cycle (163 days) was performed. A commercial feedlot located in northwestern Argentina was enrolled with cattle fed mixed rations (forage and increasing grain diet) and a convenience-experimental design was conducted. A pen (n = 21 animals) was assigned to each experimental group that received probiotics during three different periods. Groups of n = 7 animals were sampled at 40, 104 and 163 days and these samples were then pooled to one, thus giving a total of 34 samples that were subjected to high-throughput sequencing. The microbial diversity of fecal samples was significantly affected (p < 0.05) by the administration period compared with probiotic group supplementation. Even though, the three experimental periods of probiotic administration induced changes in the relative abundance of the most representative bacterial communities, the fecal microbiome of samples was dominated by the Firmicutes (72-98%) and Actinobacteria (0.8-27%) phyla, while a lower abundance of Bacteroidetes (0.08-4.2%) was present. Probiotics were able to modulate the fecal microbiota with a convergence of Clostridiaceae, Lachnospiraceae, Ruminococcaceae and Bifidobacteriaceae associated with health and growth benefits as core microbiome members. Metabolic functional prediction comparing three experimental administration periods (40, 104 and 163 days) showed an enrichment of metabolic pathways related to complex plant-derived polysaccharide digestion as well as amino acids and derivatives during the first 40 days of probiotic supplementation. Genomic-based knowledge on the benefits of autochthonous probiotics on cattle gastrointestinal tract (GIT) microbiota composition and functions will contribute to their selection as antibiotic alternatives for commercial feedlot.

Influence of microbial probiotics on ruminant health and nutrition: sources, mode of action and implications

Globally, ruminant production contributes immensely to the supply of the highest quality and quantity of proteins for human consumption, sustenance of livelihoods, and attainment of food security. Nevertheless, the phasing out of antibiotics in animal production has posed a myriad of challenges, including poor growth, performance and nutrient utilization, pathogen colonization, dysbiosis, and food safety issues in ruminants. Probiotics (direct-fed microbials), comprising live microbial strains that confer health and nutritional benefits to the host when administered in appropriate quantities, are emerging as a viable, safe, natural and sustainable alternative to antibiotics. Although the mechanisms of action exerted by probiotics on ruminants are not well elucidated, dietary probiotic dosage to ruminants enhances development and maturation, growth and performance, milk production and composition, nutrient digestibility, feed efficiency, pathogen reduction, and mitigation of gastrointestinal diseases. However, the beneficial response to probiotic supplementation in ruminants is not consistent, being dependent on the microbial strain selected, combination of strains, dose, time and frequency of supplementation, diet, animal breed, physiological stage, husbandry practice, and farm management. Nonetheless, several studies have recently reported beneficial effects of probiotics on ruminant performance, health and production. This review conclusively re-iterates the need for probiotics inclusion for the sustainability of ruminant production. Considering the role that ruminants play in food production and employment, global acceptance of sustainable ruminant production through supplementation with probiotics will undoubtedly ensure food security and food safety for the world. © 2021 Society of Chemical Industry.

Innovative Treatments Enhancing the Functionality of Gut Microbiota to Improve Quality and Microbiological Safety of Foods of Animal Origin

The gastrointestinal tract, or gut, microbiota is a microbial community containing a variety of microorganisms colonizing throughout the gut that plays a crucial role in animal health, growth performance, and welfare. The gut microbiota is closely associated with the quality and microbiological safety of foods and food products originating from animals. The gut microbiota of the host can be modulated and enhanced in ways that improve the quality and safety of foods of animal origin. Probiotics—also known as direct-fed microbials—competitive exclusion cultures, prebiotics, and synbiotics have been utilized to achieve this goal. Reducing foodborne pathogen colonization in the gut prior to slaughter and enhancing the chemical, nutritional, or sensory characteristics of foods (e.g., meat, milk, and eggs) are two of many positive outcomes derived from the use of these competitive enhancement–based treatments in food-producing animals.

Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Implication and challenges of direct-fed microbial supplementation to improve ruminant production and health

Direct-fed microbials (DFMs) are feed additives containing live naturally existing microbes that can benefit animals' health and production performance. Due to the banned or strictly limited prophylactic and growth promoting usage of antibiotics, DFMs have been considered as one of antimicrobial alternatives in livestock industry. Microorganisms used as DFMs for ruminants usually consist of bacteria including lactic acid producing bacteria, lactic acid utilizing bacteria and other bacterial groups, and fungi containing Saccharomyces and Aspergillus. To date, the available DFMs for ruminants have been largely based on their effects on improving the feed efficiency and ruminant productivity through enhancing the rumen function such as stabilizing ruminal pH, promoting ruminal fermentation and feed digestion. Recent research has shown emerging evidence that the DFMs may improve performance and health in young ruminants, however, these positive outcomes were not consistent among studies and the modes of action have not been clearly defined. This review summarizes the DFM studies conducted in ruminants in the last decade, aiming to provide the new knowledge on DFM supplementation strategies for various ruminant production stages, and to identify what are the potential barriers and challenges for current ruminant industry to adopt the DFMs. Overall literature research indicates that DFMs have the potential to mitigate ruminal acidosis, improve immune response and gut health, increase productivity (growth and milk production), and reduce methane emissions or fecal shedding of pathogens. More research is needed to explore the mode of action of specific DFMs in the gut of ruminants, and the optimal supplementation strategies to promote the development and efficiency of DFM products for ruminants.

Probiotics-Live Biotherapeutics: a Story of Success, Limitations, and Future Prospects-Not Only for Humans

In livestock production, lactic acid bacteria (LAB) represent the most widespread microorganisms used as probiotics. For such critical use, these bacteria must be correctly identified and characterized to ensure their safety and efficiency. Recently, probiotics have become highly recognized as supplements for humans and in particular for animals because of their beneficial outcome on health improvement and well-being maintenance. Various factors, encompassing dietary and management constraints, have been demonstrated to tremendously influence the structure, composition, and activities of gut microbial communities in farm animals. Previous investigations reported the potential of probiotics in animal diets and nutrition. But a high rate of inconsistency in the efficiency of probiotics has been reported. This may be due, in a major part, to the dynamics of the gastrointestinal microbial communities. Under stressing surroundings, the direct-fed microbials may play a key role as the salient limiting factor of the severity of the dysbiosis caused by disruption of the normal intestinal balance. Probiotics are live microorganisms, which confer health benefits on the host by positively modifying the intestinal microflora. Thus, the aim of this review is to summarize and to highlight the positive influence of probiotics and potential probiotic microbe supplementation in animal feed with mention of several limitations.

Evaluating the effects of Lactobacillus animalis and Propionibacterium freudenreichii on performance and rumen and fecal measures in lactating dairy cows

Two experiments evaluated the effect of supplementation with a bacterial direct-fed microbial on performance and apparent total-tract nutrient digestion of dairy cows. In experiment 1, 30 multiparous cows (75 ± 32 d in milk) were randomly assigned to 1 of 2 treatments fed for 10 wk. All cows were fed a diet containing 23.8% starch. Treatments were top dressed to rations twice daily and consisted of a combination of Lactobacillus animalis (1 × 10⁹ cfu/d) and Propionibacterium freudenreichii (2 × 10⁹ cfu/d; LAPF) or carrier alone (CON). In experiment 2, 6 ruminally cannulated cows (123 ± 129 d in milk) were randomly assigned to a crossover design with two 6-wk periods. Cows received the same CON or LAPF treatment as in experiment 1. Cows were fed the same 23.8% starch diet as experiment 1 during wk 1 through 5 of each period, and then cows were abruptly switched to a 31.1% starch diet for wk 6. For both experiments, intake and milk yield were measured daily, and milk samples were collected weekly. In experiment 1, fecal grab samples were collected every 6 h on d 7 of experimental wk 1, 2, 4, 6, 8, and 10. Fecal consistency was scored, and fecal starch was measured in daily composite samples. Fecal composites from a subset of 7 cows per treatment were used to measure apparent total-tract nutrient digestion. In experiment 2, rumen pH was continuously recorded during wk 5 and 6. On d 7 of wk 5 (the final day of feeding the 23.8% starch ration), d 1 of wk 6 (the day of diet transition), and d 7 of wk 6 (the final day of feeding the 31.1% starch ration), rumen in situ digestion was determined. Samples of rumen fluid and feces were collected every 6 h on those days for measurement of fecal starch (composited by cow within day), rumen volatile fatty acids, and fecal pH. Rumen and fecal samples were collected at one time point on those days for microbiota assessment. In experiment 1, treatment did not affect intake, milk yield, milk composition, or fecal score. The LAPF treatment decreased fecal starch percentage and tended to increase starch digestion compared with CON, but the differences were very small (0.59 vs. 0.78% and 98.74 vs. 98.46%, respectively). Digestion of other nutrients was unaffected. In experiment 2, LAPF increased rumen pH following the abrupt switch to the high-starch diet, but milk yield was lower for LAPF compared with CON (35.7 vs. 33.2 kg/d). Contrary to the decrease in fecal starch with LAPF observed in experiment 1, fecal starch tended to be increased by LAPF following the abrupt ration change in experiment 2 (2.97 vs. 2.15%). Few effects of treatment on rumen and fecal microbial populations were detectable. Under the conditions used in our experiments, addition of the bacterial direct-fed microbials did not have a marked effect on animal performance, ruminal measures, or total-tract nutrient digestion.

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.

An Overview of the Elusive Passenger in the Gastrointestinal Tract of Cattle: The Shiga Toxin Producing Escherichia coli

For approximately 10,000 years, cattle have been our major source of meat and dairy. However, cattle are also a major reservoir for dangerous foodborne pathogens that belong to the Shiga toxin-producing Escherichia coli (STEC) group. Even though STEC infections in humans are rare, they are often lethal, as treatment options are limited. In cattle, STEC infections are typically asymptomatic and STEC is able to survive and persist in the cattle GIT by escaping the immune defenses of the host. Interactions with members of the native gut microbiota can favor or inhibit its persistence in cattle, but research in this direction is still in its infancy. Diet, temperature and season but also industrialized animal husbandry practices have a profound effect on STEC prevalence and the native gut microbiota composition. Thus, exploring the native cattle gut microbiota in depth, its interactions with STEC and the factors that affect them could offer viable solutions against STEC carriage in cattle.

Treatment Strategies for Infections With Shiga Toxin-Producing Escherichia coli

Infections with Shiga toxin-producing Escherichia coli (STEC) cause outbreaks of severe diarrheal disease in children and the elderly around the world. The severe complications associated with toxin production and release range from bloody diarrhea and hemorrhagic colitis to hemolytic-uremic syndrome, kidney failure, and neurological issues. As the use of antibiotics for treatment of the infection has long been controversial due to reports that antibiotics may increase the production of Shiga toxin, the recommended therapy today is mainly supportive. In recent years, a variety of alternative treatment approaches such as monoclonal antibodies or antisera directed against Shiga toxin, toxin receptor analogs, and several vaccination strategies have been developed and evaluated in vitro and in animal models. A few strategies have progressed to the clinical trial phase. Here, we review the current understanding of and the progress made in the development of treatment options against STEC infections and discuss their potential.

Use of Lactic Acid Bacteria to Reduce Methane Production in Ruminants, a Critical Review

Enteric fermentation in ruminants is the single largest anthropogenic source of agricultural methane and has a significant role in global warming. Consequently, innovative solutions to reduce methane emissions from livestock farming are required to ensure future sustainable food production. One possible approach is the use of lactic acid bacteria (LAB), Gram positive bacteria that produce lactic acid as a major end product of carbohydrate fermentation. LAB are natural inhabitants of the intestinal tract of mammals and are among the most important groups of microorganisms used in food fermentations. LAB can be readily isolated from ruminant animals and are currently used on-farm as direct-fed microbials (DFMs) and as silage inoculants. While it has been proposed that LAB can be used to reduce methane production in ruminant livestock, so far research has been limited, and convincing animal data to support the concept are lacking. This review has critically evaluated the current literature and provided a comprehensive analysis and summary of the potential use and mechanisms of LAB as a methane mitigation strategy. It is clear that although there are some promising results, more research is needed to identify whether the use of LAB can be an effective methane mitigation option for ruminant livestock.

Could probiotics be the panacea alternative to the use of antimicrobials in livestock diets?

Probiotics are most frequently derived from the natural microbiota of healthy animals. These bacteria and their metabolic products are viewed as nutritional tools for promoting animal health and productivity, disease prevention and therapy, and food safety in an era defined by increasingly widespread antimicrobial resistance in bacterial pathogens. In contemporary livestock production, antimicrobial usage is indispensable for animal welfare, and employed to enhance growth and feed efficiency. Given the importance of antimicrobials in both human and veterinary medicine, their effective replacement with direct-fed microbials or probiotics could help reduce antimicrobial use, perhaps restoring or extending the usefulness of these precious drugs against serious infections. Thus, probiotic research in livestock is rapidly evolving, aspiring to produce local and systemic health benefits on par with antimicrobials. Although many studies have clearly demonstrated the potential of probiotics to positively affect animal health and inhibit pathogens, experimental evidence suggests that probiotics' successes are modest, conditional, strain-dependent, and transient. Here, we explore current understanding, trends, and emerging applications of probiotic research and usage in major livestock species, and highlight successes in animal health and performance.

Bacteriocin Occurrence and Activity in Escherichia coli Isolated from Bovines and Wastewater

The increasing prevalence of antimicrobial resistant (AMR) E. coli and related Enterobacteriaceae is a serious problem necessitating new mitigation strategies and antimicrobial agents. Bacteriocins, functionally diverse toxins produced by most microbes, have long been studied for their antimicrobial potential. Bacteriocins have once again received attention for their role as probiotic traits that could mitigate pathogen burden and AMR bacteria in livestock. Here, bacteriocins were identified by activity screening and whole-genome sequencing of bacteriocin-producers capable of inhibiting bovine and wastewater E. coli isolates enriched for resistance to cephalosporins. Producers were tested for activity against shiga toxin-producing E. coli (STEC), AMR E. coli, and related enteric pathogens. Multiple bacteriocins were found in 14 out of 90 E. coli isolates tested. Based on alignment within BACTIBASE, colicins M, B, R, Ia, Ib, S4, E1, E2, and microcins V, J25, and H47, encoded by identical, variant, or truncated genes were identified. Although some bacteriocin-producers exhibited activity against AMR and STEC E. coli in agar-based assays, most did not. Despite this idiosyncrasy, liquid co-cultures of all bacteriocinogenic isolates with luciferase-expressing generic (K12) or STEC E. coli (EDL933) resulted in inhibited growth or reduced viability. These abundant toxins may have real potential as next-generation control strategies in livestock production systems but separating the bacteriocin from its immunity gene may be necessary for such a strategy to be effective.

Management of STEC Gastroenteritis: Is There a Role for Probiotics?

Shiga toxin-producing Escherichia Coli (STEC) infections routinely run as a common gastroenteritis, but in many cases they may evolve towards hemolytic uremic syndrome (HUS). HUS is a rare disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Gut microorganisms have a fundamental impact on human physiology, because they modulate normal intestinal functions and play a pivotal role in influencing the local and systemic immune responses. Despite surveillance established in many countries and major progresses in the understanding of STEC-HUS mechanisms, no specific treatment is currently available. Targeting the gut microbiota could represent a new potential therapeutic strategy in STEC infection. In this paper, we reviewed the current knowledge about microbiota characteristics of patients with STEC infections, as well as in vitro and in vivo evidence of probiotic supplementation in managing STEC gastroenteritis and in HUS onset prevention.

Dissect the mode of action of probiotics in affecting host-microbial interactions and immunity in food producing animals

Prophylactic antimicrobials have been widely used in food animal production with the aim to prevent infectious diseases, enhance feed efficiency, and promote growth. However, the extensive use of antimicrobials in food animal production systems has led to the emergence of antimicrobial resistant pathogens, which are potential threats to human and animal health. Probiotics have been proposed to be a promising alternative of prophylactic antimicrobials, with potential beneficial effects on the host animal by improving the balance of intestinal microbiota and host immunity. Although an increasing body of evidence shows that probiotics could directly or indirectly affect gut microbiota and host immune functions, the lack of the understanding of how probiotics influence host-microbial interaction and immunity is one of the reasons for controversial findings from many animal trials, especially in food production animals. Therefore, in this review we focused on the most recent (last ten years) studies on how gut microbiota and host immune function changes in response to probiotics in food production animals (swine, poultry, and ruminant). In addition, the relationship between microbial changes and host immune function was illustrated, and how such relationship differs among animal species was further compared. Moreover, the future directions concerning the mechanisms of how probiotics modulate host-microbial interactions and host immunity were highlighted, which may assist in the optimal supplementation strategy to maximize the efficacy of probiotics to improve animal gut health and productivity.

Antimicrobial Stewardship in Veterinary Medicine

While antimicrobial resistance is already a public health crisis in human medicine, therapeutic failure in veterinary medicine due to antimicrobial resistance remains relatively uncommon. However, there are many pathways by which antimicrobial resistance determinants can travel between animals and humans: by close contact, through the food chain, or indirectly via the environment. Antimicrobial stewardship describes measures that can help mitigate the public health crisis and preserve the effectiveness of available antimicrobial agents. Antimicrobial stewardship programs have been principally developed, implemented, and studied in human hospitals but are beginning to be adapted for other applications in human medicine. Key learning from the experiences of antimicrobial stewardship programs in human medicine are summarized in this article-guiding the development of a stewardship framework suitable for adaptation and use in both companion animal and livestock practice. The antimicrobial stewardship program for veterinary use integrates infection prevention and control together with approaches emphasizing avoidance of antimicrobial agents. The 5R framework of continuous improvement that is described recognizes the importance of executive support; highly motivated organizations and teams (responsibility); the need to review the starting position, set objectives, and determine means of measuring progress and success; and a critical focus on reducing, replacing, and refining the use of antimicrobial agents. Significant issues that are currently the focus of intensive research include improved detection and diagnosis of infections, refined dosing regimens that are simultaneously effective while not selecting resistance, searches for alternatives to antimicrobial agents, and development of improved vaccines to enhance immunity and reduce disease.

Molecular detection and quantification of viable probiotic strains in animal feedstuffs using the commercial direct fed microbial Lactobacillus animalis NP51 as a model

Lactobacillus animalis NP51 is a direct-fed microbial strain (DFM) extensively used as a pre-harvest food safety mitigation in feedlot cattle due to its antagonistic effects against human foodborne pathogens such as Salmonella and Escherichia coli O157:H7. NP51 not only promotes overall gut health but interferes with the ability of these pathogens to colonize the gastrointestinal tract of cattle. As a result, NP51 reduces fecal shedding of Salmonella and E. coli O157:H7 in cattle presented for harvest and the load of these pathogens that enter the human food chain. Cattle are administered a high dose (1 × 10⁹ CFU/head/day) of NP51 to reduce fecal shedding of foodborne pathogens. Ensiled animal feedstuffs naturally contain a high load of lactic acid bacteria (LAB) and it is not possible to detect and quantify the level of a specific LAB strain (e.g., NP51) in this matrix using traditional microbiological culture. The purpose of this study was to develop a molecular method to detect and quantify viable populations of a specific LAB strain (e.g., NP51) in cattle feedstuffs. The NP51 whole genome sequence was aligned with closely related LAB clustering within the same well-supported clade in a LAB phylogeny derived from 30 conserved amino acid encoding sequence to identify orthologs. A sequence encoding recombinational DNA repair protein RecT was found to be unique to NP51 and used to design primers and a probe for molecular detection and quantification of NP51. The primers and probe were confirmed to be specific to NP51 in vitro. Total RNA was extracted from silage samples, including samples naturally inoculated in the field and control samples that were artificially spiked with a range of NP51 concentrations in the laboratory. Reverse-transcriptase quantitative real-time (RT-qRTi) PCR was used to quantify cDNA copies in samples and cycle threshold (Ct) values were compared to a standard curve to estimate NP51 concentrations. Our results indicate this novel molecular method is suitable to confirm the presence and estimate the concentration of a specific LAB strain in animal feedstuffs containing high background levels of LAB.

Multi-Exposure Pathway Model to Compare Escherichia coli O157 Risks and Interventions

The relative contributions of exposure pathways associated with cattle-manure-borne Escherichia coli O157:H7 on public health have yet to be fully characterized. A stochastic, quantitative microbial risk assessment (QMRA) model was developed to describe a hypothetical cattle farm in order to compare the relative importance of five routes of exposure, including aquatic recreation downstream of the farm, consumption of contaminated ground beef processed with limited interventions, consumption of leafy greens, direct animal contact, and the recreational use of a cattle pasture. To accommodate diverse environmental and hydrological pathways, existing QMRAs were integrated with novel and simplistic climate and field-level submodels. The model indicated that direct animal contact presents the greatest risk of illness per exposure event during the high pathogen shedding period. However, when accounting for the frequency of exposure, using a high-risk exposure-receptor profile, consumption of ground beef was associated with the greatest risk of illness. Additionally, the model was used to evaluate the efficacy of hypothetical interventions affecting one or more exposure routes; concurrent evaluation of multiple routes allowed for the assessment of the combined effect of preharvest interventions across exposure pathways-which may have been previously underestimated-as well as the assessment of the effect of additional downstream interventions. This analysis represents a step towards a full evaluation of the risks associated with multiple exposure pathways; future incorporation of variability associated with environmental parameters and human behaviors would allow for a comprehensive assessment of the relative contribution of exposure pathways at the population level.

Enterohaemorrhagic and other Shiga toxin-producing Escherichia coli (STEC): Where are we now regarding diagnostics and control strategies?

Escherichia coli comprises a highly diverse group of Gram-negative bacteria and is a common member of the intestinal microflora of humans and animals. Generally, such colonization is asymptomatic; however, some E. coli strains have evolved to become pathogenic and thus cause clinical disease in susceptible hosts. One pathotype, the Shiga toxigenic E. coli (STEC) comprising strains expressing a Shiga-like toxin is an important foodborne pathogen. A subset of STEC are the enterohaemorrhagic E. coli (EHEC), which can cause serious human disease, including haemolytic uraemic syndrome (HUS). The diagnosis of EHEC infections and the surveillance of STEC in the food chain and the environment require accurate, cost-effective and timely tests. In this review, we describe and evaluate tests now in routine use, as well as upcoming test technologies for pathogen detection, including loop-mediated isothermal amplification (LAMP) and whole-genome sequencing (WGS). We have considered the need for improved diagnostic tools in current strategies for the control and prevention of these pathogens in humans, the food chain and the environment. We conclude that although significant progress has been made, STEC still remains an important zoonotic issue worldwide. Substantial reductions in the public health burden due to this infection will require a multipronged approach, including ongoing surveillance with high-resolution diagnostic techniques currently being developed and integrated into the routine investigations of public health laboratories. However, additional research requirements may be needed before such high-resolution diagnostic tools can be used to enable the development of appropriate interventions, such as vaccines and decontamination strategies.

Lactobacillus reuteri suppresses E. coli O157:H7 in bovine ruminal fluid: Toward a pre-slaughter strategy to improve food safety?

The bovine gastrointestinal tract (GIT) is the main reservoir for enterohaemorrhagic Escherichia coli (EHEC) responsible for food-borne infections. Therefore, it is crucial to develop strategies, such as EHEC suppression by antagonistic microorganisms, to reduce EHEC survival in the GIT of cattle and to limit shedding and food contamination. Most human-derived Lactobacillus reuteri strains produce hydroxypropionaldehyde (HPA), an antimicrobial compound, during anaerobic reduction of glycerol. The capacity of L. reuteri LB1-7, a strain isolated from raw bovine milk, to produce HPA and its antimicrobial activity against an O157:H7 EHEC strain (FCH6) were evaluated in bovine rumen fluid (RF) under strict anaerobiosis. EHEC was totally suppressed when incubated in RF inoculated with L. reuteri LB1-7 and supplemented with 80 mM glycerol (RF-Glyc80). The addition of LB1-7 or glycerol alone did not modify EHEC survival in RF. Glycerol was converted to HPA (up to 14 mM) by LB1-7 during incubation in RF-Glyc80, and HPA production appeared to be responsible for EHEC suppression. The bactericidal activity of L. reuteri LB1-7, the concentration of glycerol required and the level of HPA produced depended on physiological and ecological environments. In vitro experiments also showed that EHEC inoculated in rumen fluid and exposed to L. reuteri and glycerol had a very limited growth in rectal contents. However, L. reuteri exerted an antimicrobial activity against the rumen endogenous microbiota and perturbed feedstuff degradation in the presence of glycerol. The potential administration of L. reuteri and glycerol in view of application to finishing beef cattle at the time of slaughter is discussed. Further in vivo studies will be important to confirm the efficiency of L. reuteri and glycerol supplementation against EHEC shedding in ruminants.

Introduction to Preharvest Food Safety

This introductory article provides an overview of preharvest food safety activities and initiatives for the past 15 years. The section on traditional areas of preharvest food safety focuses on significant scientific advancements that are a culmination of collaborative efforts (both public health and agriculture) and significant research results. The highlighted advancements provide the foundation for exploring future preharvest areas and for improving and focusing on more specific intervention/control/prevention strategies. Examples include Escherichia coli and cattle, Salmonella and Campylobacter in poultry, and interventions and prevention and control programs. The section on "nontraditional" preharvest food safety areas brings attention to potential emerging food safety issues and to future food safety research directions. These include organic production, the FDA's Produce Rule (water and manure), genomic sequencing, antimicrobial resistance, and performance metrics. The concluding section emphasizes important themes such as strategic planning, coordination, epidemiology, and the need for understanding food safety production as a continuum. Food safety research, whether at the pre- or postharvest level, will continue to be a fascinating complex web of foodborne pathogens, risk factors, and scientific and policy interactions. Food safety priorities and research must continue to evolve with emerging global issues, emerging technologies, and methods but remain grounded in a multidisciplinary, collaborative, and systematic approach.

Potential for Meta-Analysis in the Realm of Preharvest Food Safety

Meta-analysis, the statistical combination of results from multiple studies, can be used to summarize all of the available research on an intervention, etiology, descriptive, or diagnostic test accuracy question. Meta-analysis should be conducted as a component of a systematic review, to increase transparency in the selection of studies and to incorporate an evaluation of the risk of bias in the individual studies included in the meta-analysis. The process of meta-analysis may include a forest plot to graphically display the study results and the calculation of a weighted average summary effect size. Heterogeneity (differences in the effect size between studies) can be evaluated using formal statistics and the reasons for heterogeneity can be explored using sub-group analysis or meta-regression. Thus, meta-analysis may be a useful methodology for preharvest food safety research to aid in policy or clinical decision-making or to provide input to quantitative risk assessment or other models.

Human microbiome versus food-borne pathogens: friend or foe

As food safety advances, there is a great need to maintain, distribute, and provide high-quality food to a much broader consumer base. There is also an ever-growing "arms race" between pathogens and humans as food manufacturers. The human microbiome is a collective organ of microbes that have found community niches while associating with their host and other microorganisms. Humans play an important role in modifying the environment of these organisms through their life choices, especially through individual diet. The composition of an individual's diet influences the digestive system-an ecosystem with the greatest number and largest diversity of organisms currently known. Organisms living on and within food have the potential to be either friends or foes to the consumer. Maintenance of this system can have multiple benefits, but lack of maintenance can lead to a host of chronic and preventable diseases. Overall, this dynamic system is influenced by intense competition from food-borne pathogens, lifestyle, overall diet, and presiding host-associated microbiota.

Saltelli Global Sensitivity Analysis and Simulation Modelling to Identify Intervention Strategies to Reduce the Prevalence of Escherichia coli O157 Contaminated Beef Carcasses

Introduction

Strains of Shiga-toxin producing Escherichia coli O157 (STEC O157) are important foodborne pathogens in humans, and outbreaks of illness have been associated with consumption of undercooked beef. Here, we determine the most effective intervention strategies to reduce the prevalence of STEC O157 contaminated beef carcasses using a modelling approach.

Method

A computational model simulated events and processes in the beef harvest chain. Information from empirical studies was used to parameterise the model. Variance-based global sensitivity analysis (GSA) using the Saltelli method identified variables with the greatest influence on the prevalence of STEC O157 contaminated carcasses. Following a baseline scenario (no interventions), a series of simulations systematically introduced and tested interventions based on influential variables identified by repeated Saltelli GSA, to determine the most effective intervention strategy.

Results

Transfer of STEC O157 from hide or gastro-intestinal tract to carcass (improved abattoir hygiene) had the greatest influence on the prevalence of contaminated carcases. Due to interactions between inputs (identified by Saltelli GSA), combinations of interventions based on improved abattoir hygiene achieved a greater reduction in maximum prevalence than would be expected from an additive effect of single interventions. The most effective combination was improved abattoir hygiene with vaccination, which achieved a greater than ten-fold decrease in maximum prevalence compared to the baseline scenario.

Conclusion

Study results suggest that effective interventions to reduce the prevalence of STEC O157 contaminated carcasses should initially be based on improved abattoir hygiene. However, the effect of improved abattoir hygiene on the distribution of STEC O157 concentration on carcasses is an important information gap—further empirical research is required to determine whether reduced prevalence of contaminated carcasses is likely to result in reduced incidence of STEC O157 associated illness in humans. This is the first use of variance-based GSA to assess the drivers of STEC O157 contamination of beef carcasses.