Enterica Contamination Research Articles

CRISPR/Cas12a-Triggered Visible-Light-Driven Photoelectrochemical Assay with Single-Nucleotide Resolution for Drug-Resistant Foodborne Salmonella Detection.

The prevalence of foodborne pathogenic bacteria, especially drug-resistant strains, such as Salmonella enterica, poses serious threats to public health, highlighting the requirement for the development of rapid and precise detection methods. Herein, a CRISPR/Cas12a-triggered visible-light-driven photoelectrochemical (PEC) assay (CasPEC) was developed using a SiO2-quenched BiVO4/MoS2 p/n-type heterojunction as the photoactive material. The CRISPR/Cas12a recognition endowed the CasPEC assay with high specificity capable of resolving single-nucleotide polymorphisms (SNPs) and identifying SNP-involved drug-resistant bacteria. SiO2 was linked to the surface of the BiVO4/MoS2 heterojunction by single-stranded DNA (ssDNA), which would be cleaved by target-activated CRISPR/Cas12a. This cleavage of ssDNA resulted in the detachment of SiO2, thereby achieving a "signal-on" PEC output. Leveraging the multiple-turnover CRISPR cleavage and the outstanding photoactive performance of PEC signaling, the CasPEC assay for S. enterica showed a detection limit of 103 colony-forming units (CFU)/mL and the ability to detect as few as 0.01% drug-resistant strains. The CasPEC assay can accurately sense the S. enterica contamination in complex food matrices, including beef and milk. These findings demonstrated the great potential of the CasPEC assay for detecting pathogenic bacterial contamination in food, particularly concerning food safety related to SNP-involved drug-resistant bacteria.

Endoprotein-activating DNAzyme assay for nucleic acid extraction- and amplification-free detection of viable pathogenic bacteria

Pathogenic bacteria in food or environment, can pose threats to public health, highlighting the requirement of tools for rapid and accurate detection of viable pathogenic bacteria. Herein, we report a sequential endoprotein RNase H2-activating DNAzyme assay (termed epDNAzyme) that enables nucleic acid extraction- and amplification-free detection of viable Salmonella enterica (S. enterica). The direct detection allows for a rapid detection of viable S. enterica within 25 min. Besides, the assay, based on sequential reporting strategy, circumvents internal modifications in the DNAzyme's active domain and improve its catalytic activity. The multiple-turnover DNAzyme cutting and the enhanced catalytic activity of DNAzyme render the epDNAzyme assay to be highly sensitive, and enables the detection of 190 CFU/mL and 0.1% viable S. enterica. The assay has been utilized to detect S. enterica contamination in food and clinical samples, indicating its potential as a promising tool for monitoring pathogen-associated biosafety.

Strain typing and antimicrobial susceptibility of Salmonella enterica Albany isolates from duck farms in South Korea

Salmonella enterica is distributed worldwide and is a common cause of bacterial food poisoning in humans and a serious public health problem. Although duck meat consumption has recently increased in Korea, studies on the epidemiological relationship between S. enterica contamination in duck farms are scarce. Salmonella enterica serovar Albany isolates recovered from duck farms were analyzed using two typing methods — IR Biotyper® (IRBT) and multilocus variable-number tandem repeat analysis (MLVA). The clustering results were compared with the epidemiological survey findings and the antimicrobial resistance profiles. From April 2019 to October 2020, 20 individual feces per farm from 5–6-week-old ducks were collected repeatedly from 105 duck farms. Salmonella spp. isolated from duck feces were identified using PCR and multilocus sequence typing to investigate the prevalence and distribution of the Salmonella serovars. The prevalence of S. enterica was 19%, and S. enterica Albany was the predominantly recovered isolate. The S. enterica Albany isolates underwent antimicrobial susceptibility testing to determine the minimum inhibitory concentration. MLVA and IRBT methods established relatedness and diversity among the S. enterica Albany isolates. Multidrug-resistant S. enterica Albany was distributed in all the farms. Antimicrobial resistance profiles reflected the duck farm characteristics and isolates recovered from the same farm showed an identical profile. Isolates repeatedly recovered from the same farm also showed identical IRBT clusters and MLVA groups. These findings suggest that the isolates remained on the duck farm and re-infected new duck flocks. Thus, proper cleaning and disinfection is required before the farms are repopulated.

Мультирезистентные к антибиотикам штаммы и гены вирулентности salmonella strains, выделенной из мяса кур (Ханой, Вьетнам)

Salmonella enterica is one of dangerous food-borne pathogens listed by the World Health Organization (WHO). In Vietnam, poultry is one of the most widely eaten meats and is reported as a common source of S. enterica contamination. The aim of this study was to examine multi-resistant Salmonella strains, to identify susceptibility to antibiotics by using 15 different types of medications and to perform sequencing to analyze antibiotic resistance genes, genotypes, multi-locus sequence-based typing (MLST), and plasmids. The result of the antibiotic susceptibility test indicated that phenotypic resistance to 9–11 types of antimicrobials was confirmed in all strains. Among 06 sequenced strains, we identified 43 genes associated with antibiotic resistance: strains carrying a range of genes that are associated with aminoglycoside resistance (aac(3), aac(6), ant(3), aph(3), aph(6), aadA); all strains carried blaCTX-M-55 or blaCTX-M-65 gene, which were resistant to the 3rd generation antibiotics; there were also frequently observed sul1, sul2, sul3, tet (A), qnrS1, floR, dfrA14 or dfrA27 genes in sequenced isolates. Besides, the genome sequencing also indicated that all strains carried pathogenicity islands SPI 1, SPI 2, and SPI 3 thereby creating many potential triggers of the disease. Additionally, some carried C63PI, SPI 9, SPI 13, SPI 14, and plus some plasmids such as Col156, IncHI2, IncHI2A, IncFIB, Col (MGD2).

Strains and virulence genes of salmonella with multidrug resistance isolated from chicken carcasses (Hanoi, Vietnam)

Salmonella enterica is one of dangerous food-borne pathogens listed by the World Health Organization (WHO). In Vietnam, poultry is one of the most widely eaten meats and is reported as a common source of S. enterica contamination. The aim of this study was to examine multi-resistant Salmonella strains, to identify susceptibility to antibiotics by using 15 different types of medications and to perform sequencing to analyze antibiotic resistance genes, genotypes, multi-locus sequence-based typing (MLST), and plasmids. The result of the antibiotic susceptibility test indicated that phenotypic resistance to 9–11 types of antimicrobials was confirmed in all strains. Among 06 sequenced strains, we identified 43 genes associated with antibiotic resistance: strains carrying a range of genes that are associated with aminoglycoside resistance (aac(3), aac(6), ant(3), aph(3), aph(6), aadA); all strains carried blaCTX-M-55 or blaCTX-M-65 gene, which were resistant to the 3rd generation antibiotics; there were also frequently observed sul1, sul2, sul3, tet (A), qnrS1, floR, dfrA14 or dfrA27 genes in sequenced isolates. Besides, the genome sequencing also indicated that all strains carried pathogenicity islands SPI 1, SPI 2, and SPI 3 thereby creating many potential triggers of the disease. Additionally, some carried C63PI, SPI 9, SPI 13, SPI 14, and plus some plasmids such as Col156, IncHI2, IncHI2A, IncFIB, Col (MGD2).

Direct Detection of Foodborne Pathogens via a Proximal DNA Probe-Based CRISPR-Cas12 Assay.

Foodborne pathogens can cause illnesses. Existing tools for detecting foodborne pathogens are typically time-consuming or require complex protocols. Here, we report an assay to directly analyze pathogenic genes based on CRISPR-Cas12. This new test, termed proximal DNA probe-based CRISPR-Cas12 (PPCas12), facilitates the detection of foodborne pathogens without amplification steps. The elimination of the nucleic acid amplification process dramatically reduced the processing time, complexity, and costs in the analysis of foodborne pathogens. The substitution of the frequently used dually labeled DNA reporter with a proximal DNA probe in the PPCas12 assay led to a 4-fold sensitivity enhancement. PPCas12 offered a limit of detection of 619 colony-forming units in the detection of Salmonella enterica (S. enterica) without the nucleic acid amplification process. The specific recognition of genes via PPCas12 allowed distinguishing S. enterica from other foodborne pathogens. The PPCas12 assay was applied in the screening of S. enterica contamination on fresh eggs with high precision. Hence, the new PPCas12 assay will be a valuable tool for on-site monitoring of foodborne pathogens.

Salmonella Contamination of Seafood in Landing Centers and Retail Markets of Mumbai, India.

Seafood contamination with Salmonella enterica is not only a public health concern, but can also lead to economic losses due to import rejections. Continuous monitoring of seafood for Salmonella is necessary for risk assessment and to establish suitable control measures. The objective of this study was to determine the extent of Salmonella contamination of seafood in fish landing centers and retails markets. In this study, we analyzed seafood samples from three fish landing centers and seven retail markets of Mumbai, India for S. enterica contamination. Salmonella was isolated using multiple selective enrichment broths and selective agars, and identified by conventional biochemical tests followed by polymerase chain reaction (PCR). Of 82 samples of seafood, comprising both finfish and shellfish, Salmonella was detected in 17 (20.7%) finfish samples. None of the shellfish samples (shrimps, clams, and cephalopods) were found to be contaminated with Salmonella. Samples from both landing centers and fish markets, as well as from pelagic and demersal sources, harbored Salmonella. Source-wise analysis showed that 11 of 57 (19.3%) samples from retail fish markets and 6 of 25 (24%) samples from fish landing centers were contaminated with Salmonella. The study emphasizes the need to implement measures to prevent anthropogenic contamination of coastal waters and improve the hygiene of retail fish markets in Mumbai. Seafood from landing centers and retail markets, as well as from pelagic and demersalhabitats were similarly contaminated with Salmonella. Fish species widely consumed in the region of this study were found highly contaminated with Salmonella.

Inhibition of Salmonella enterica growth by competitive exclusion during early alfalfa sprout development using a seed-dwelling Erwinia persicina strain EUS78

Salmonella enterica outbreaks in sprouts originate from contaminated seeds; conventional prevention technologies have been reported from many research institutes. In this study, we applied a biological control approach to inhibit S. enterica growth using the seed-dwelling non-antagonistic bacteria. We isolated non-antibacterial seed-dwelling bacteria from vegetable sprouts. A total of 206 bacteria exhibiting non-antibacterial activity against S. enterica were subjected to alfalfa sprout development tests. Eight isolates exhibiting no deleterious effect on the growth of alfalfa sprouts were tested for S. enterica growth inhibition on alfalfa seeds and sprouts, and an isolate EUS78 was finally selected for further investigation. Based on 16S rRNA, gyrB, and rpoB gene sequence analyses, strain EUS78 was identified as Erwinia persicina. In population competition, the S. enterica population increased by >3 log CFU/g after 6 days of alfalfa sprout growth, whereas S. enterica growth was significantly inhibited by treatment with EUS78 (P < .05). This effect of S. enterica growth inhibition by EUS78 was sustained until the end of the alfalfa sprout harvest. Overall, bacterial strain EUS78 significantly reduced S. enterica growth on alfalfa sprouts in a manner consistent with competitive exclusion. These findings led us to monitor EUS78 behavior on seeds during early sprout development using fluorescence and scanning electron microscopy. Strain EUS78 initially colonized alfalfa sprout seed coat edges, cotyledons, and finally root surfaces during early sprout germination. As alfalfa sprouts grew, EUS78 bacterial cells established colonies on newly emerged plant tissues such as root tips. The results of this study suggest that strain EUS78 has potential as a biological control agent to inhibit S. enterica contamination in the sprout food industry.

Survival of Salmonella Newport on Whole and Fresh-Cut Cucumbers Treated with Lytic Bacteriophages

Salmonella enterica associated with consumption of cucumbers ( Cucumis sativus ) has led to foodborne outbreaks in the United States. Whole and fresh-cut cucumbers are susceptible to S. enterica contamination during growing, harvesting, and postharvest handling. The application of lytic bacteriophages specific for S. enterica was evaluated to reduce Salmonella populations on cucumbers. Unwaxed cucumbers ('Lisboa' variety, or mini-cucumbers purchased at retail) were inoculated with Salmonella Newport (5 log CFU per cucumber) and were sprayed with 3.2 mL of phosphate-buffered saline (control) or 10 log PFU/ml of SalmoFresh, a Salmonella-specific bacteriophage preparation (phage), to deliver 4.76 × 107 PFU/cm2. Cucumbers were stored at 10 or 22°C for 7 days. Inoculated mini-cucumbers were sliced with a sterile knife to investigate Salmonella transfer to mesocarp, and cut pieces were stored at 4°C for 2 days. Populations (log CFU per cucumber) of Salmonella Newport on phage-treated whole cucumbers were significantly (P < 0.05) smaller (2.44 ± 0.94) than on control-treated cucumbers (4.27 ± 0.37) on day 0. Populations on phage-treated cucumbers stored at 10°C were 1.72 ± 0.77 and 1.56 ± 0.46, which were significantly lower than those on control-treated cucumbers (3.20 ± 0.48 and 2.33 ± 0.25) on days 1 and 4, respectively. Between days 0 and 1, populations on control-treated cucumbers stored at 10 and 22°C declined by 1.07 and 2.47 log CFU per cucumber, respectively. At 22°C, Salmonella Newport populations declined by 2.37 log CFU per cucumber between days 0 and 1. Phage application to whole cucumbers before slicing did not reduce the transfer of Salmonella Newport to fresh-cut slices. Lytic phage application may be a potential intervention to reduce Salmonella populations on whole cucumbers.

Salmonella Enterica Prevalence in Finishing Pigs at Slaughter Plants in Northern Italy.

Finishing pigs carrying Salmonella enterica are believed to be the main source of carcass contamination at the beginning of slaughtering. The aim of this study was to assess the S. enterica carrier status of finishing pigs at herd level by sampling pooled faeces on farm and mesenteric lymph nodes at slaughter in the North East of Italy. Environmental faecal samples belonging to 30 batches of pigs were collected on farm. At slaughter, mesenteric lymph nodes were collected from five randomly selected pigs per batch. S. enterica was isolated from 16 lymph nodes out of 150 (10.6%) and from seven out of 30 (23.3%) faecal samples. Four batches (13.3%) were positive to S. enterica both in lymph nodes and in faeces. The number of batches positive to S. enterica either in lymph nodes or in faeces was 13 out of 30 (43.3%). The most prevalent serovars from lymph nodes were S. Derby (25.0%) and S. Typhimurium monophasic variant 1, 4,[5],12:i:- (18.6%), which were also isolated from faecal material (14.3 and 42.8% respectively). Contaminated faecal material or lymph nodes could be a primary source of carcass contamination at slaughter during evisceration. S. enterica contamination is widespread on pig farms and carrier pigs pass undetected the inspection visits at slaughter, entering the food chain. Therefore, in order to control S. enterica in pigs, the need to quantify possible risk factors at slaughter and develop effective management strategies on farm is of paramount importance to ensure food safety.

Modeling the Fate of Escherichia coli O157:H7 and Salmonella enterica in the Agricultural Environment: Current Perspective

The significance of fresh vegetable consumption on human nutrition and health is well recognized. Human infections with Escherichia coli O157:H7 and Salmonella enterica linked to fresh vegetable consumption have become a serious public health problem inflicting a heavy economic burden. The use of contaminated livestock wastes such as manure and manure slurry in crop production is believed to be one of the principal routes of fresh vegetable contamination with E. coli O157:H7 and S. enterica at preharvest stage because both ruminant and nonruminant livestock are known carriers of E. coli O157:H7 and S. enterica in the environment. A number of challenge-testing studies have examined the fate of E. coli O157:H7 and S. enterica in the agricultural environment with the view of designing strategies for controlling vegetable contamination preharvest. In this review, we examined the mathematical modeling approaches that have been used to study the behavior of E. coli O157:H7 and S. enterica in the manure, manure-amended soil, and in manure-amended soil-plant ecosystem during cultivation of fresh vegetable crops. We focused on how the models have been applied to fit survivor curves, predict survival, and assess the risk of vegetable contamination preharvest. The inadequacies of the current modeling approaches are discussed and suggestions for improvements to enhance the applicability of the models as decision tools to control E. coli O157:H7 and S. enterica contamination of fresh vegetables during primary production are presented.

Potential Interactions between Salmonella enterica and Ralstonia solanacearum in Tomato Plants

Over the past decade, the Eastern Shore of Virginia (ESV) has been implicated in at least four outbreaks of salmonellosis associated with tomato, all originating from the same serovar, Salmonella enterica serovar Newport. In addition to Salmonella Newport contamination, the devastating plant disease bacterial wilt, caused by the phytopathogen Ralstonia solanacearum, threatens the sustainability of ESV tomato production. Bacterial wilt is present in most ESV tomato fields and causes devastating yield losses each year. Although the connection between bacterial wilt and tomato-related salmonellosis outbreaks in ESV is of interest, the relationship between the two pathogens has never been investigated. In this study, tomato plants were root dip inoculated with one of four treatments: (i) 8 log CFU of Salmonella Newport per ml, (ii) 5 log CFU of R. solanacearum per ml, (iii) a coinoculation of 8 log CFU of Salmonella Newport per ml plus 5 log CFU of R. solanacearum per ml, and (iv) sterile water as control. Leaf, stem, and fruit samples were collected at the early-green-fruit stage, and S. enterica contamination in the internal tissues was detected. S. enterica was recovered in 1.4 and 2.9% of leaf samples from plants inoculated with Salmonella Newport only and from plants coinoculated with Salmonella Newport plus R. solanacearum, respectively. S. enterica was recovered from 1.7 and 3.5% of fruit samples from plants inoculated with Salmonella Newport only and from plants coinoculated with Salmonella Newport plus R. solanacearum, respectively. There were significantly more stem samples from plants coinoculated with Salmonella Newport plus R. solanacearum that were positive for S. enterica (18.6%) than stem samples collected from plants inoculated with Salmonella Newport only (5.7%). Results suggested that R. solanacearum could influence S. enterica survival and transportation throughout the internal tissues of tomato plants.

Cross-sectional Study ExaminingSalmonella entericaCarriage in Subiliac Lymph Nodes of Cull and Feedlot Cattle at Harvest

Bovine peripheral lymph nodes (LNs), including subiliac LNs, have been identified as a potential source of human exposure to Salmonella enterica, when adipose trim containing these nodes is incorporated into ground beef. In order to gain a better understanding of the burden of S. enterica in peripheral LNs of feedlot and cull cattle, a cross-sectional study was undertaken in which 3327 subiliac LNs were collected from cattle at harvest in seven plants, located in three geographically distinct regions of the United States. Samples were collected in three seasons: Fall 2010, Winter/Spring 2011, and Summer/Fall 2011. A convenience sample of 76 LNs per day, 2 days per season (approximately 1 month apart), was collected per plant, from carcasses held in the cooler for no less than 24 h. Every 10(th) carcass half on a rail was sampled, in an attempt to avoid oversampling any single cohort of cattle. Median point estimates of S. enterica contamination were generally low (1.3%); however, median Salmonella prevalence was found to be greater in subiliac LNs of feedlot cattle (11.8%) compared to those of cull cattle (0.65%). Enumeration analysis of a subset of 618 feedlot cattle LNs showed that 67% of those harboring S. enterica (97 of 144) did so at concentrations ranging from <0.1 to 1.8 log10 CFU/g, while 33% carried a higher burden of S. enterica, with levels ranging from 1.9 to >3.8 log10 CFU/g. Serotyping of S. enterica isolated identified 24 serotypes, with the majority being Montevideo (44.0%) and Anatum (24.8%). Antimicrobial susceptibility phenotypes were determined for all isolates, and the majority (86.1%) were pansusceptible; however, multidrug-resistant isolates (8.3%) were also occasionally observed. As Salmonella contained within LNs are protected from carcass interventions, research is needed to define opportunities for mitigating the risk of Salmonella contamination in LNs of apparently healthy cattle.

The Effect of European Starlings and Ambient Air Temperature on Salmonella enterica Contamination within Cattle Feed Bunks

European starlings (Sturnus vulgaris) are a known risk factor for the occurrence of microorganisms that are pathogenic to cattle and humans in concentrated animal feeding operations (CAFOs). Starling use of CAFOs is known to vary in response to weather; starling control operations on CAFOs often are timed to coincide with favorable environmental conditions to maximize take. The totality of this information suggests that disease risks in CAFOs associated with starlings may be infl uenced by environmental factors, such as temperature. In this study, we assessed the risk of Salmonella enterica contamination of cattle feed by modeling the interaction between starling numbers and ambient air temperatures using data previously reported from Texas CAFOs. We compared these interaction models to the previously published additive models for S. enterica contamination of cattle feed using an information-theoretic approach to model selection that ranked and weighted models in terms of their support by the data, using bias-adjusted Akaike's Information Criterion (AIC c ) and Akaike weights (Wi). Our results indicate that the interaction between European starlings and ambient air temperature better explained the occurrence of S. enterica in cattle feed than any of the previously reported models. Specifi cally, the risk of S. enterica contamination of cattle feed by starlings was greatest when winter temperatures were highest (10°C). Thus, we conclude that the risk of S. enterica contamination of cattle feed by starlings will be worst on the few winter days when daytime high temperatures are above freezing and large numbers of birds are present. Because these conditions will be most common in the late winter and early spring, we recommend that starling control operations on feedlots and dairies be conducted as early in the winter as possible to mitigate the risks of disease created by large foraging fl ocks of starlings.

High hydrostatic pressure processing reduces Salmonella enterica serovars in diced and whole tomatoes

Fresh and fresh-cut tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. One effective post harvest treatment to reduce Salmonella enterica in tomatoes may be high pressure processing (HPP). The objectives of the study were to determine the potential for HPP to reduce S. enterica serovars Newport, Javiana, Braenderup and Anatum in tryptic soy broth (TSB) and to determine the effect of HPP to reduce the most pressure resistant of the four serovars from fresh diced and whole tomatoes. To evaluate pressure resistance, TSB containing 8 log CFU/ml of one of the four serovars was packaged in sterile stomacher bags and subjected to one of three different pressures (350, 450 or 550MPa) for 120s. The most pressure resistant S. enterica serovar evaluated was Braenderup. Subjecting the broth culture to 350, 450 and 550MPa resulted in a 4.53, 5.74 and 7.09 log reduction in S. Braenderup, respectively. Diced tomatoes (150g) and whole red round tomatoes (approximately 150g) were inoculated with 0.1ml of 9.1 log CFU/ml S. Braenderup, and subjected to the same pressure treatments (350, 450 or 550MPa). Significant reductions of S. Braenderup concentrations in diced tomatoes (P<0.05) were seen after processing at 350 (0.46CFU/g), 450 (1.44 log CFU/g), and 550MPa (3.67 log CFU/g). In whole tomatoes, significant reductions (P<0.05) were also seen at 350 (1.41 log CFU/g), 450 (2.25 log CFU/g) and 550MPa (3.35 log CFU/g). HPP may be an effective post harvest strategy to reduce low levels of S. enterica contamination in whole and diced tomatoes.

The role of starlings in the spread of Salmonella within concentrated animal feeding operations

Summary 1. Characterizing and mitigating the disease risks associated with wildlife use of concentrated animal feeding operations (CAFOs) can reduce the spread of micro‐organisms throughout the environment while increasing agricultural productivity. To better understand the disease risks associated with bird use of CAFOs, we assessed the capacity of European starlings Sturnus vulgaris to spread Salmonella enterica to cattle, their feed and water. 2. We sampled starlings, cattle feed, cattle water and cattle faeces from 10 CAFOs in Texas, USA. Samples were screened for Salmonella enterica to investigate: (i) the prevalence of S. enterica in starlings using CAFOs, (ii) whether there was a relationship between cattle infections and starling numbers, and (iii) if S. enterica contamination of cattle feed and water was related to numbers of starlings observed on CAFOs. 3. We used generalized linear mixed logistic regression models to assess the importance of starlings, cattle stocking, facility management and environmental variables in the transmission of S. enterica to cattle, feed troughs and water troughs in CAFOs. 4. Starling gastrointestinal tract samples tested positive for S. enterica (2·5% prevalence; 95% CI = 0·3%, 8·6%) and starlings were retained as model covariates in the best supported logistic regression models for S. enterica contamination within cattle feed, water and faeces. 5. Salmonella enterica contamination of both cattle feed troughs and water troughs is significantly related to numbers of starlings. Contamination in cattle feed increased as more starlings entered feed troughs. Contamination in water troughs increased asymptotically as numbers of starlings on CAFOs increased. Starling variables in the cattle faecal shedding model were not significant. 6. Synthesis and applications. The numbers of European starlings better explained S. enterica contamination of cattle feed and water than other variables including cattle stocking, facility management and environmental variables. This suggests that starlings are a source of S. enterica contamination in CAFOs. Thus, starling management tools such as population control, habitat management, exclusionary devises and bird repellents may be used to reduce the amplification and spread of disease within livestock production systems.