Influence of inoculation route on the carrier state of Salmonella choleraesuis in swine

Evaluation of immunogenicity and protective efficacy of outer membrane vesicles from Salmonella Typhimurium and Salmonella Choleraesuis

Outer membrane vesicles (OMVs) are membranous structures frequently observed in Gram-negative bacteria that contain bioactive substances. These vesicles are rich in bacterial antigens that can activate the host's immune system, making them a promising candidate vaccine to prevent and manage bacterial infections. The aim of this study was to assess the immunogenicity and protective efficacy of OMVs derived from Salmonella enterica serovar Typhimurium and S. Choleraesuis, while also focusing on enhancing OMV production. Initial experiments showed that OMVs from wild-type strains did not provide complete protection against homologous Salmonella challenge, possible due to the presence of flagella in the purified OMVs samples, which may elicit an unnecessary immune response. To address this, flagellin-deficient mutants of S. Typhimurium and S. Choleraesuis were constructed, designated rSC0196 and rSC0199, respectively. These mutants exhibited reduced cell motility and their OMVs were found to be flagellin-free. Immunization with non-flagellin OMVs derived from rSC0196 induced robust antibody responses and improved survival rates in mice, as compared to the OMVs derived from the wild-type UK-1. In order to enhance OMV production, deletions of ompA or tolR were introduced into rSC0196. The deletion of tolR not only increase the yield of OMVs, but also conferred complete protection against homologous S. Typhimurium challenge in mice. Collectively, these findings indicate that the flagellin-deficient OMVs with a tolR mutation have the potential to serve as a versatile vaccine platform, capable of inducing broad-spectrum protection against significant pathogens.

Salmonella Infection in Pigs: Disease, Prevalence, and a Link between Swine and Human Health

Salmonella is one of the most spread foodborne pathogens worldwide, and Salmonella infections in humans still represent a global health burden. The main source of Salmonella infections in humans is represented by contaminated animal-derived foodstuffs, with pork products being one of the most important players. Salmonella infection in swine is critical not only because it is one of the main causes of economic losses in the pork industry, but also because pigs can be infected by several Salmonella serovars, potentially contaminating the pig meat production chain and thus posing a significant threat to public health globally. As of now, in Europe and in the United States, swine-related Salmonella serovars, e.g., Salmonella Typhimurium and its monophasic variant Salmonella enterica subsp. enterica 1,4,[5],12:i:-, are also frequently associated with human salmonellosis cases. Moreover, multiple outbreaks have been reported in the last few decades which were triggered by the consumption of Salmonella-contaminated pig meat. Throughout the years, changes and evolution across the pork industry may have acted as triggers for new issues and obstacles hindering Salmonella control along the food chain. Gathered evidence reinforces the importance of coordinating control measures and harmonizing monitoring programs for the efficient control of Salmonella in swine. This is necessary in order to manage outbreaks of clinical disease in pigs and also to protect pork consumers by controlling Salmonella subclinical carriage and shedding. This review provides an update on Salmonella infection in pigs, with insights on Salmonella ecology, focusing mainly on Salmonella Choleraesuis, S. Typhimurium, and S. 1,4,[5],12:i:-, and their correlation to human salmonellosis cases. An update on surveillance methods for epidemiological purposes of Salmonella infection in pigs and humans, in a "One Health" approach, will also be reported.

Inoculation of Weaned Pigs by Feed, Water, and Airborne Transmission of Salmonella enterica Serotype 4,[5],12:i:

ABSTRACT

Salmonella enterica serotype 4,[5],12:i:- (STM) has become an increasing problem for food safety and has been often detected in swine products. Weanling pigs were exposed to STM-contaminated feed, water, or air to determine possible STM transmission routes. A control group of pigs was included. STM was monitored daily in feces and rectal and nasal swabs. STM colonization was most prevalent in tissues from tonsil, lower intestine, and mesenteric lymph nodes. No differences in lesion severity were observed between inoculated and control pigs. Contaminated feed, water, and aerosolized particles caused infection in weaned pigs; however, no STM colonization was observed in skeletal muscle destined for human consumption. Based on the results from this study, STM contamination in pork products most likely results from cross-contamination of meat by digesta or lymph node tissue during processing.

HIGHLIGHTS

Bacillus-Based Direct-Fed Microbial Reduces the Pathogenic Synergy of a Coinfection with Salmonella enterica Serovar Choleraesuis and Porcine Reproductive and Respiratory Syndrome Virus

Viral respiratory infections predispose lungs to bacterial coinfections causing a worse outcome than either infection alone. Porcine reproductive and respiratory syndrome virus (PRRSV) causes pneumonia in pigs and is often associated with bacterial coinfections. We examined the impact of providing weanling pigs a Bacillus-based direct-fed microbial (DFM) on the syndrome resulting from infection with either Salmonella enterica serotype Choleraesuis alone, or in combination with PRRSV. Nine days after the bacterial challenge, Salmonella was isolated from ileocecal lymph nodes of all challenged pigs regardless of DFM treatment. Compared to the single bacterial challenge, the dual challenge with Salmonella and PRRSV resulted in a pathogenic synergy exhibited by a higher rate of Salmonella colonization in the lung and a more extensive and severe interstitial pneumonia. Provision of DFM to dually challenged pigs reduced the rate of lung colonization by Salmonella, eliminated or reduced the presence of PRRSV in the lung, and reduced the extent and severity of gross lung pathology. Dually challenged pigs that received DFM had increased concentrations of interleukin 1 (IL-1) and IL-8 in lung lavage fluids, accompanied by increased expression in their blood cells of nucleotide-binding oligomerization domain receptor 2 (NOD2) and triggering receptor expressed in myeloid cells 1 (TREM-1) molecules. These changes in pulmonary inflammatory cytokine production and increased expression of NOD2 and TREM-1 suggest that the DFM exerted a systemic modulating effect on innate immunity. These observations are consistent with the notion that tonic stimulation by gut-derived microbial products can poise innate immunity to fight infections in the respiratory tract.

The role of TolA, TolB, and TolR in cell morphology, OMVs production, and virulence of Salmonella Choleraesuis

The Tol–Pal system of Gram-negative bacteria is necessary for maintaining outer membrane integrity. It is a multiprotein complex of five envelope proteins, TolQ, TolR, TolA, TolB, and Pal. These proteins were first investigated in E. coli, and subsequently been identified in many other bacterial genera. However, the function of the Tol–Pal system in Salmonella Choleraesuis pathogenesis is still unclear. Here, we reported the role of three of these proteins in the phenotype and biology of S. Choleraesuis. We found that mutations in tolA, tolB, and tolR caused severe damage to the cell wall, which was supported by observing the microstructure of spherical forms, long chains, flagella defects, and membrane blebbing. We confirmed that all the mutants significantly decreased S. Choleraesuis survival when exposed to sodium deoxycholate and exhibited a high sensitivity to vancomycin, which may be explained by the disruption of envelope integrity. In addition, tolA, tolB, and tolR mutants displayed attenuated virulence in a mouse infection model. This could be interpreted as a series of defective phenotypes in the mutants, such as severe defects in envelope integrity, growth, and motility. Further investigation showed that all the genes participate in outer membrane vesicles (OMVs) biogenesis. Interestingly, immunization with OMVs from ΔtolB efficiently enhanced murine viability in contrast to OMVs from the wild-type S. Choleraesuis, suggesting its potential use in vaccination strategies. Collectively, this study provides an insight into the biological role of the S. Choleraesuis Tol–Pal system.

Sudden death associated with bleeding into digestive system of finishing pigs – a review

Sudden deaths of finishing pigs in modern pig herds cause economic losses and therefore draw constant attention worldwide. In the case of peracute mortality associated with gastrointestinal bleeding, pigs usually die during a short period without clinical manifestations. Necropsy can detect bleeding into various parts of the digestive system. Determining the exact aetiology of the sudden death can be difficult in many cases. Diseases and conditions such as gastric ulcers, abdominal torsion, haemorrhagic bowel syndrome and infectious diseases should be taken into account in the differential diagnosis. Because some of these diseases still have an unclear aetiology and pathogenesis, the aim of our work was to provide a summary of existing knowledge as well as to describe related pathognomonic pathological changes.

Outbreaks of antimicrobial resistant Salmonella Choleraesuis in wild boars piglets from central-western Spain

Salmonella enterica serovar Choleraesuis is the aetiological agent of swine paratyphoid being a highly invasive zoonotic pathogen. Wild boar natural populations are experiencing a demographical expansion as well as some farms are breeding this species to release for hunting with management sometimes identical to that of domestic pigs, including supplementation, grouping, and antibiotic treatments. This situation increases the chance of contact between wild boars and livestock, and potentially induces stress, with different sanitary consequences. The present work aims to describe the clinical features of recent outbreaks caused by S. Choleraesuis in wild boar from central-western Spain, as well as the antimicrobial resistance and phylogenetic relationships of isolates involved. 28 strains of S. Choleraesuis were isolated from 28 different wild boars belonging to 10 different game states located in central western Spain and submitted to the Clinical Veterinary Hospital (CVH) of the University of Extremadura. Samples were taken from different organs and cultured according to the ISO 6579:2002 procedure. Suspicious colonies were identified by PCR and antimicrobial resistance was evaluated by disc diffusion susceptibility test and the presence of the main resistance genes as well as 18 plasmid replicons frequently found among the Enterobacteriaceae was verified by PCR. Pulsed field gel electrophoresis was applied to determine the genetic relationship between isolates. The outbreaks under study were characterized by high mortality (35%-84%) and a septicaemic presentation. S. Choleraesuis was isolated from all the wild boars analysed, and 26 of the 28 isolates presented resistance to at least one antibiotic. The predominant resistances found were against sulphonamide, streptomycin, tetracycline, and doxicicline and sul1, strA-strB, and tetA were the most prevalent resistance genes among isolates. 10 strains carried FIIA, FIB+H/1 or FIIA+H/1 plasmids. PFGE classified the isolates into four different profiles, grouped into two clusters. This results show that prevention against S. Choleraesuis must be considered in the sanitary programs of the wild boar breeders.

Combined effects of spray-drying conditions and postdrying storage time and temperature on Salmonella choleraesuis and Salmonella typhimurium survival when inoculated in liquid porcine plasma

The objective of this study was to determine the effectiveness of the spray-drying process on the inactivation of Salmonella choleraesuis and Salmonella typhimurium spiked in liquid porcine plasma and to test the additive effect of immediate postdrying storage. Commercial spray-dried porcine plasma was sterilized by irradiation and then reconstituted (1:9) with sterile water. Aliquots of reconstituted plasma were inoculated with either S. choleraesuis or S. typhimurium, subjected to spray-drying at an inlet temperature of 200°C and an outlet temperature of either 71 or 80°C, and each spray-drying temperature combinations were subjected to either 0, 30 or 60 s of residence time (RT) as a simulation of residence time typical of commercial dryers. Spray-dried samples were stored at either 4·0 ± 3·0°C or 23·0 ± 0·3°C for 15 days. Bacterial counts of each Salmonella spp., were completed for all samples. For both Salmonella spp., spray-drying at both outlet temperatures reduced bacterial counts about 3 logs at RT 0 s, while there was about a 5·5 log reduction at RT 60 s. Storage of all dried samples at either 4·0 ± 3·0°C or 23·0 ± 0·3°C for 15 days eliminate all detectable bacterial counts of both Salmonella spp.

SIGNIFICANCE AND IMPACT OF THE STUDY

Safety of raw materials from animal origin like spray-dried porcine plasma (SDPP) may be a concern for the swine industry. Spray-drying process and postdrying storage are good inactivation steps to reduce the bacterial load of Salmonella choleraesuis and Salmonella typhimurium. For both Salmonella spp., spray-drying at 71°C or 80°C outlet temperatures reduced bacterial counts about 3 log at residence time (RT) 0 s, while there was about a 5.5 log reduction at RT 60 s. Storage of all dried samples at either 4.0 ± 3.0°C or 23.0 ± 0.3°C for 15 days was effective for eliminating detectable bacterial counts of both Salmonella spp.

Salmonella Choleraesuis outer membrane vesicles: Proteomics and immunogenicity

Salmonella enterica serotype Choleraesuis (S. Choleraesuis), Gram-negative facultative intracellular pathogen is capable of inducing the cholera in pigs whose symptoms manifest as fever, depression, septicemia, arthritis, and diarrhea. Infections with S. Choleraesuis has resulted in great economic loss for the swine breeding operations. Bacterial outer membrane vesicles (OMVs) play an important role in pathogenicity and host-pathogen interaction. In this study, we purified OMVs released by S. Choleraesuis strain χ3545 and characterized their lipopolysaccharide (LPS) profile. The OMVs contained intact LPS molecules. By using LC-MS/MS, we identified 192 proteins in the OMVs. In addition, the subcellular location and biological functions of the vesicles was predicted. The proteins were mainly derived from outer membranes and cytoplasm. Several proteins were immunoreactive and associated with the secretion pathway. Some putative multi-drug resistance-associated proteins were also identified. Furthermore, immunization experiment via intranasal or intraperitoneal route in mice demonstrated that S. Choleraesuis OMVs could elicit strong humoral and mucosal immune responses. Although OMVs as vaccine did not provide strong protection against clinical strain of wild-type S. Choleraesuis, immunization of OMVs still prolonged the survival time of vaccinated mice after high dose of S. Choleraesuis infection. Overall, this study provides valuable fundamental information toward elucidating the pathogenicity and functions of OMVs secreted from S. Choleraesuis.

Ultraviolet (UV-C) inactivation of Enterococcus faecium, Salmonella choleraesuis and Salmonella typhimurium in porcine plasma

The objective of this study was to assess the effectiveness of an ultraviolet (UV-C, 254 nm) irradiation system on reducing the load of Salmonella typhimurium (S. typhimurium), Salmonella choleraesuis (S. choleraesuis) resistant to streptomycin and Enterococcus faecium (E. faecium) inoculated in sterile porcine plasma and then subjected to different UV-C irradiation doses (750, 1500, 3000, 6000 and 9000 J/L) using a pilot plant UV-C device working under turbulent flow. Results indicated that UV-C treatment induced a viability reduction of 0.38, 1.18, 3.59, 4.72 and 5.06 log10 S. typhimurium when irradiated at 750, 1500, 3000, 6000 and 9000 J/L, respectively. The observed log10 reduction of S. choleraesuis was 1.44, 2.68, 5.55, 7.07 and 7.97 at 750, 1500, 3000, 6000 and 9000 J/L, respectively. The best-fit inactivation for S. choleraesuis was the Weibull distribution curve, while the best-fit curve for S. typhimurium was the Weibull plus tail model, indicating that around 10² cfu/mL resistant S. typhimurium was detected when the liquid plasma was UV-C irradiated at doses up to 9000 J/L. Viability reduction for E. faecium was 0.44, 1.01, 3.70, 5.61 and 6.22 log10 when irradiated at 750, 1500, 3000, 6000 and 9000 J/L, respectively, with no bacterial resistance observed with UV-C doses of 6000 J/L or higher. The biphasic model was the best fit model for the inactivation curve for E. faecium. For the three microorganisms tested, about a 4 log-unit reduction was achieved when the liquid plasma was irradiated at 3000J/L. Overall results demonstrate the usefulness of the UV-C system to inactivate bacteria in liquid plasma before spray-drying. We conclude that the UV-C system can provide an additional biosafety feature that can be incorporated into the manufacturing process for spray-dried animal plasma.

Vaccination as a control strategy against Salmonella infection in pigs: A systematic review and meta-analysis of the literature

Consumption or handling of improperly processed or cooked pork is considered one of the top sources for foodborne salmonellosis, a common cause of intestinal disease worldwide. Asymptomatic carrier pigs may contaminate pork at slaughtering; therefore, pre-harvest reduction of Salmonella load can contribute to reduce public health risk. Multiple studies have evaluated the impact of vaccination on controlling Salmonella in swine farms, but results are highly variable due to the heterogeneity in vaccines and vaccination protocols. Here, we report the results of an inclusive systematic review and a meta-analysis of the peer-reviewed scientific literature to provide updated knowledge on the potential effectiveness of Salmonella vaccination. A total of 126 articles describing the use of Salmonella vaccines in swine were identified, of which 44 fulfilled the inclusion criteria. Most of the studies (36/44) used live vaccines, and S. Typhimurium and S. Choleraesuis were the predominant serotypes evaluated. Vaccine efficacy was most often measured through bacteriological isolation, and pooled estimates of vaccine efficacy were obtained as the difference in the percentage of positive animals when available. Attenuated and inactivated vaccines had similar efficacy [Risk Difference=-26.8% (-33.8, -19.71) and -29.5% (-44.4, -14.5), respectively]. No serotype effect was observed on the efficacy recorded for attenuated vaccines; however, a higher efficacy of inactivated vaccines against S. Choleraesuis was observed, though in a reduced sample. Results from the meta-analysis here demonstrate the impact that vaccination may have on the control of Salmonella in swine farms and could help in the design of programs to minimize the risk of transmission of certain serotypes through the food chain.

Salmonella Vaccination in Pigs: A Review

The control of Salmonella enterica in pig production is necessary for both public and animal health. The persistent and frequently asymptomatic nature of porcine Salmonella infection and the organism's abilities to colonize other animal species and to survive in the environment mean that effective control generally requires multiple measures. Vaccination is one such measure, and the present review considers its role and its future, drawing on studies in pigs from the 1950s to the present day. Once established in the body as an intracellular infectious agent, Salmonella can evade humoral immunity, which goes some way to explaining the often disappointing performance of inactivated Salmonella vaccines. More recent approaches, using mucosal presentation of antigens, live vaccines and adjuvants to enhance cell-mediated immunity, have met with more success. Vaccination strategies that involve stimulating both passive immunity from the dam plus active immunity in offspring appear to be most efficacious, although either approach alone can yield significant control of Salmonella. Problems that remain include relatively poor control of Salmonella serovars that are dissimilar to the vaccine antigen mix, and difficulties in measuring and predicting the performance of candidate vaccines in ways that are highly relevant to their likely use in commercial production.

Effectiveness of simulated interventions in reducing the estimated prevalence of Salmonella in UK pig herds

Salmonella spp are a major foodborne zoonotic cause of human illness. Consumption of pork products is believed to be a major source of human salmonellosis and Salmonella control throughout the food-chain is recommended. A number of on-farm interventions have been proposed, and some have been implemented in order to try to achieve Salmonella control. In this study we utilize previously developed models describing Salmonella dynamics to investigate the potential effects of a range of these on-farm interventions. As the models indicated that the number of bacteria shed in the faeces of an infectious animal was a key factor, interventions applied within a high-shedding scenario were also analysed. From simulation of the model, the probability of infection after Salmonella exposure was found to be a key driver of Salmonella transmission. The model also highlighted that minimising physiological stress can have a large effect but only when shedding levels are not excessive. When shedding was high, weekly cleaning and disinfection was not effective in Salmonella control. However it is possible that cleaning may have an effect if conducted more often. Furthermore, separating infectious animals, shedding bacteria at a high rate, from the rest of the population was found to be able to minimise the spread of Salmonella.

Semi-stochastic models for Salmonella infection within finishing pig units in the UK

A multi-group semi-stochastic model is formulated to describe Salmonella dynamics on a pig herd within the UK and assess whether farm structure has any effect on the dynamics. The models include both direct transmission and indirect (via free-living infectious units in the environment and airborne infection). The basic reproduction number R0 is also investigated. The models estimate approximately 24.6% and 25.4% of pigs at slaughter weight will be infected with Salmonella within a slatted-floored and solid-floored unit respectively, which corresponds to values found in previous abattoir and farm studies, suggesting that the model has reasonable validity. Analysis of the models identified the shedding rate to be of particular importance in the control of Salmonella spread, a finding also evident in an increase in the R0 value.

Intraspecies variation in the emergence of hyperinfectious bacterial strains in nature

Salmonella is a principal health concern because of its endemic prevalence in food and water supplies, the rise in incidence of multi-drug resistant strains, and the emergence of new strains associated with increased disease severity. Insights into pathogen emergence have come from animal-passage studies wherein virulence is often increased during infection. However, these studies did not address the prospect that a select subset of strains undergo a pronounced increase in virulence during the infective process- a prospect that has significant implications for human and animal health. Our findings indicate that the capacity to become hypervirulent (100-fold decreased LD₅₀) was much more evident in certain S. enterica strains than others. Hyperinfectious salmonellae were among the most virulent of this species; restricted to certain serotypes; and more capable of killing vaccinated animals. Such strains exhibited rapid (and rapidly reversible) switching to a less-virulent state accompanied by more competitive growth ex vivo that may contribute to maintenance in nature. The hypervirulent phenotype was associated with increased microbial pathogenicity (colonization; cytotoxin production; cytocidal activity), coupled with an altered innate immune cytokine response within infected cells (IFN-β; IL-1β; IL-6; IL-10). Gene expression analysis revealed that hyperinfectious strains display altered transcription of genes within the PhoP/PhoQ, PhoR/PhoB and ArgR regulons, conferring changes in the expression of classical virulence functions (e.g., SPI-1; SPI-2 effectors) and those involved in cellular physiology/metabolism (nutrient/acid stress). As hyperinfectious strains pose a potential risk to human and animal health, efforts toward mitigation of these potential food-borne contaminants may avert negative public health impacts and industry-associated losses.

Salmonellosis continues to compromise human health, animal welfare, and modern agriculture. Developing a comprehensive control plan requires an understanding of how pathogens emerge and express traits that confer increased incidence and severity of disease. It is well-established that animal passage often results in increased virulence; however, our findings indicate that the capacity to undergo a pronounced increase in virulence after passage was much more prevalent in certain Salmonella isolates than in others. The resultant hyperinfectious strains are among the most virulent salmonellae reported; were restricted to certain serotypes; and were able to override the immunity conferred in vaccinated animals. The induction of hypervirulence was responsive to subtle changes in environmental conditions and, potentially, may occur in other salmonellae serotypes after passage through certain hosts and/or exposure to certain environmental variables; a response that may be common across the microbial realm. Thus, management practices and environmental conditions inherent to livestock production have the potential to inadvertently trigger hypervirulence (e.g., diet; herd size; exposure to livestock waste and/or antimicrobials). From a farm management perspective, careful consideration must be given to risk-management strategies that reduce emergence/persistence of these potential food-borne contaminants to safeguard public health and reduce industry-associated losses.

Roles of diet and the acid tolerance response in survival of common Salmonella serotypes in feces of finishing pigs

The persistence of Salmonella in the environment is an important factor influencing the transmission of infection in pig production. This study evaluated the effects of acid tolerance response (ATR), organic acid supplementation, and physical properties of feed on the survival of a five-strain Salmonella mixture in porcine feces held at 4 and 22°C for 88 days. Acid-adapted or non-acid-adapted nalidixic acid-resistant Salmonella strains were used to inoculate feces of pigs fed four different diets, which consisted of a nonpelleted, finely ground meal feed or a finely ground, pelleted feed that was left unsupplemented or was supplemented with K-diformate. Organic acid supplementation and physical properties of feed markedly influenced Salmonella survival, but the effects were highly dependent on storage temperature; survival was unaffected by ATR. The most pronounced effects were observed at 22°C, a temperature similar to that of finishing pig houses. The supplementation of meal diets with K-diformate significantly reduced the duration of survival (P < 0.1) and increased rates of decline (P < 0.0001) of salmonellae in feces compared to survival in feces of pigs fed unsupplemented meal. The pelleting of feed, compared to feeding meal, significantly reduced (P < 0.1) the duration of survival in feces held at 22°C. Only minor effects of feed form and acid supplementation on survivor numbers were observed at 4°C. Differences in the fecal survival of Salmonella could not be related to diet-induced changes in fecal physiochemical parameters. The predominant survival of S. enterica serovar Typhimurium DT193 and serotype 4,[5],12:i:- in porcine feces demonstrates the superior ability of these serotypes to survive in this environment. Fecal survival and transmission of Salmonella in pig herds may be reduced by dietary approaches, but effects are highly dependent on environmental temperature.

Porcine circovirus type 2 potentiates morbidity of Salmonella enterica serovar Choleraesuis in Cesarean-derived, colostrum-deprived pigs

PROBLEM ADDRESSED

Porcine circovirus type 2 (PCV2) and Salmonella enterica subspecies enterica serovar Choleraesuis (S. Choleraesuis) are two leading causes of economic loss in the swine industry. Although S. Choleraesuis infection occurs concurrently with PCV2-associated disease in many swine herds, the pathogenesis of concurrent infection with PCV2 and S. Choleraesuis remains largely undefined.

OBJECTIVE

We investigated the interactions between PCV2 and S. Choleraesuis in 20 Cesarean-derived, colostrum-deprived (CDCD) pigs randomly assigned to 4 groups (n=5 per group).

METHODS AND APPROACH

Pigs in the dual-infected and PCV2-infected groups were inoculated intranasally with PCV2 at 5 weeks of age, and pigs in the dual-infected and S. Choleraesuis-infected groups were inoculated intranasally with S. Choleraesuis at 7 weeks of age. Pigs in the control group served as uninfected controls.

RESULTS

After S. Choleraesuis inoculation, severe clinical signs, reduction of weight gain, and severe microscopic lung lesions were observed in dual-infected pigs compared to those in other groups. In addition, the pigs in the dual-infected group shed significantly (P=0.002) higher quantities of S. Choleraesuis in feces 12 days after S. Choleraesuis inoculation, and S. Choleraesuis was recovered from more tissues in this group 14 days after S. Choleraesuis inoculation.

CONCLUSIONS

These results indicate that prior PCV2 infection potentiates the severity of clinical signs, lung lesions, and fecal shedding and tissue dissemination of S. Choleraesuis in infected pigs. Therefore, dual infection of pigs with PCV2 and S. Choleraesuis may increase clinical effects of salmonellosis in the field.

Immunological, physiological, and behavioral effects of Salmonella enterica carriage and shedding in experimentally infected finishing pigs

Finishing pigs infected with Salmonella pose significant food safety risks by carrying the pathogen into abattoirs. This study was conducted to determine the dynamics of Salmonella infection in finishing pigs, and associated immunological, physiological, and behavioral alterations, by longitudinally comparing infected to noninfected pigs during 6 weeks postinfection (p.i.). Bacteriological data revealed that all inoculated pigs started shedding Salmonella within 2 h p.i., and persistently shed the bacteria up to the end of the study. Ileal and cecal contents, as well as mesenteric lymph node samples, were all positive throughout the study, containing 3-4 log(10) cfu/g of Salmonella at 24 h p.i., and 4-5 log(10) cfu/g of Salmonella up to 4 weeks p.i. Levels of Salmonella dropped markedly (p < 0.05) in all samples at 5 weeks p.i. There was no difference between groups for blood cell counts. Tumor necrosis factor-α was greater (p < 0.05) in infected pigs: (1) in the mesenteric lymph nodes by 48 h p.i.; (2) at 24 h and 3 weeks p.i. in the ileum; and (3) in the cecum and spleen at 3 weeks p.i. Interleukin-12, interleukin-1 and its antagonist, and a porcine-specific antimicrobial peptide RNA expression in tissues changed over time, but were not different between groups. Infected pigs spent more time in ventral recumbency, standing, and sitting than controls (p < 0.01). Infected pigs were also more active (p < 0.01), and approached a novel object more quickly than control pigs (p < 0.05). No treatment differences were detected for rectal temperature or plasma cortisol (p > 0.10). This study shows that finishing pigs can carry high levels of Salmonella for up to 4 weeks p.i. in the gastrointestinal contents and mesenteric lymph nodes, shedding high levels of the bacteria without developing clinical symptoms, but developing an immune response throughout the intestinal tract. Moreover, subtle behavioral changes measured as postures were detected, and therefore warrant additional investigation.

Attenuated Salmonella choleraesuis-mediated RNAi targeted to conserved regions against foot-and-mouth disease virus in guinea pigs and swine

In this study, specific sequences within three genes (3D, VP4 and 2B) of the foot-and-mouth disease virus (FMDV) genome were determined to be effective RNAi targets. These sequences are highly conserved among different serotype viruses based on sequence analysis. Small interfering RNA (siRNA)-expressing plasmids (p3D-NT19, p3D-NT56, pVP4-NT19, pVP4-NT65 and p2B-NT25) were constructed to express siRNA targeting 3D, VP4 and 2B, respectively. The antiviral potential of these siRNA for various FMDV isolates was investigated in baby hamster kidney (BHK-21) cells and suckling mice. The results show that these siRNA inhibited virus yield 10- to 300-fold for different FMDV isolates of serotype O and serotype Asia I at 48 h post infection in BHK-21 cells compared to control cells. In suckling mice, p3D-NT56 and p2B-NT25 delayed the death of mice. Twenty percent to 40% of the animals that received a single siRNA dose survived 5 days post infection with serotype O or serotype Asia I. We used an attenuated Salmonella choleraesuis (C500) vaccine strain, to carry the plasmid that expresses siRNA directed against the polymerase gene 3D (p3D-NT56) of FMDV. We used guinea pigs to evaluate the inhibitory effects of recombinant S. cho (p3D-NT56/S. cho) on FMDV infection. The results show that 80% of guinea pigs inoculated with 10⁹ CFU of p3D-NT56/S. cho and challenged 36 h later with 50 ID₅₀ of homologous FMDV were protected. We also measured the antiviral activity of p3D-NT56/S. cho in swine. The results indicate that 100% of the animals treated with 5 × 10⁹ CFU of p3D-NT56/S. cho were protected in 9 days.

Reproduction of fowl typhoid by respiratory challenge with Salmonella Gallinarum

Fowl typhoid is a disease of adult chickens and is caused by Salmonella Gallinarum infection via the alimentary tract. The experimental reproduction of fowl typhoid per os (PO) requires artificial conditions to minimize the effect of gastric acid, and several Salmonella serovars have been known to be transmitted via the respiratory route. Therefore, we have hypothesized the existence of a respiratory route for Salmonella Gallinarum infection and have attempted to reproduce fowl typhoid via intratracheal challenge. In accordance with our hypothesis, the intratracheal challenges of Salmonella Gallinarum reproduced exactly same lesions as fowl typhoid and induced higher mortality and morbidity than those of the PO challenge. Therefore, this study represents the first reproduction of fowl typhoid via respiratory route, and our findings may be useful for understanding the transmission of Salmonella Gallinarum in the field.

Human Salmonella clinical isolates distinct from those of animal origin

The global trend toward intensive livestock production has led to significant public health risks and industry-associated losses due to an increased incidence of disease and contamination of livestock-derived food products. A potential factor contributing to these health concerns is the prospect that selective pressure within a particular host may give rise to bacterial strain variants that exhibit enhanced fitness in the present host relative to that in the parental host from which the strain was derived. Here, we assessed 184 Salmonella enterica human and animal clinical isolates for their virulence capacities in mice and for the presence of the Salmonella virulence plasmid encoding the SpvB actin cytotoxin required for systemic survival and Pef fimbriae, implicated in adherence to the murine intestinal epithelium. All (21 of 21) serovar Typhimurium clinical isolates derived from animals were virulent in mice, whereas many (16 of 41) serovar Typhimurium isolates derived from human salmonellosis patients lacked this capacity. Additionally, many (10 of 29) serovar Typhimurium isolates derived from gastroenteritis patients did not possess the Salmonella virulence plasmid, in contrast to all animal and human bacteremia isolates tested. Lastly, among serovar Typhimurium isolates that harbored the Salmonella virulence plasmid, 6 of 31 derived from human salmonellosis patients were avirulent in mice, which is in contrast to the virulent phenotype exhibited by all the animal isolates examined. These studies suggest that Salmonella isolates derived from human salmonellosis patients are distinct from those of animal origin. The characterization of these bacterial strain variants may provide insight into their relative pathogenicities as well as into the development of treatment and prophylactic strategies for salmonellosis.

Rapid detection of Salmonella sp. in pork samples using fluorescent in situ hybridization: a comparison with VIDAS®-SLM system and ISO 6579 cultural method

This study reports the use of the fluorescent in situ hybridization (FISH) with Sal3 probe for Salmonella detection in swine carcasses inner surface (swab); and in the correspondent samples of ileum, ileocolic, and mandibular lymph nodes; and tonsils, after dilution (1:10) in buffered peptone water and a pre-enrichment step (37(0)C, 18h). In order to evaluate the efficiency of FISH, 235 naturally contaminated samples were simultaneously tested by the cultural method (ISO 6579) and by the Vitek Immuno Diagnostic Assay System (VIDAS®) - Salmonella (SLM) system. The cultural method identified 39 positive samples. From these, VIDAS®- SLM only detected 23. FISH identified 115 positive samples. This difference was highly significant (P<0.001). From positive samples, 32 were also confirmed by the cultural method. The results indicate FISH as a promising tool for rapid Salmonella detection in samples of pork and swine carcasses.

Salmonella induces prominent gene expression in the rat colon

Background

Salmonella enteritidis is suggested to translocate in the small intestine. In vivo it induces gene expression changes in the ileal mucosa and Peyer's patches. Stimulation of Salmonella translocation by dietary prebiotics fermented in colon suggests involvement of the colon as well. However, effects of Salmonella on colonic gene expression in vivo are largely unknown. We aimed to characterize time dependent Salmonella-induced changes of colonic mucosal gene expression in rats using whole genome microarrays. For this, rats were orally infected with Salmonella enteritidis to mimic a foodborne infection and colonic gene expression was determined at days 1, 3 and 6 post-infection (n = 8 rats per time-point). As fructo-oligosaccharides (FOS) affect colonic physiology, we analyzed colonic mucosal gene expression of FOS-fed versus cellulose-fed rats infected with Salmonella in a separate experiment. Colonic mucosal samples were isolated at day 2 post-infection.

Results

Salmonella affected transport (e.g. Chloride channel calcium activated 6, H⁺/K⁺ transporting Atp-ase), antimicrobial defense (e.g. Lipopolysaccharide binding protein, Defensin 5 and phospholipase A2), inflammation (e.g. calprotectin), oxidative stress related genes (e.g. Dual oxidase 2 and Glutathione peroxidase 2) and Proteolysis (e.g. Ubiquitin D and Proteosome subunit beta type 9). Furthermore, Salmonella translocation increased serum IFNγ and many interferon-related genes in colonic mucosa. The gene most strongly induced by Salmonella infection was Pancreatitis Associated Protein (Pap), showing >100-fold induction at day 6 after oral infection. Results were confirmed by Q-PCR in individual rats. Stimulation of Salmonella translocation by dietary FOS was accompanied by enhancement of the Salmonella-induced mucosal processes, not by induction of other processes.

Conclusion

We conclude that the colon is a target tissue for Salmonella, considering the abundant changes in mucosal gene expression.

Effects of feeding Salmonella enterica serovar Typhimurium or serovar Choleraesuis on growth performance and circulating insulin-like growth factor-I, tumor necrosis factor-α, and interleukin-1β in weaned pigs1

The most common Salmonella serovars causing clinical disease in pigs are Salmonella enterica serovars Typhimurium (Typhimurium) and Choleraesuis. Given that the swine host-adapted serovar Choleraesuis has been reported to cause systemic disease, a different disease outcome from that of Typhimurium, our working hypothesis was that this serovar would likely engage systemic immune-inflammatory mechanisms, resulting in elevated systemic cytokine secretion. Forty-eight weaned pigs were blocked by BW and sex, and randomly allotted to 1 of 3 treatments in a 14-d study. Each treatment had 8 replicates (pens), with 2 pigs/pen. The treatments consisted of a negative control and pigs repeatedly fed 10(8) cfu of Typhimurium or Choleraesuis. On d 0, the pigs were fed Choleraesuis or Typhimurium in dough balls, and the bacteria were refed twice weekly throughout the experiment. Control pigs received dough balls without bacteria. All pigs were housed in temperature-controlled rooms under constant lighting and were fed a standard corn-soybean meal-based nursery diet. Pig BW and feed disappearance were used to determine ADG, ADFI, and G:F. Rectal temperatures were obtained daily from 1 pig/pen beginning 2 d before the first bacterial feeding through d 7 using rapid-response digital thermometers. Serum was collected on d 0, 7, and 14 from a single pig/pen for analysis of IGF-I, tumor necrosis factor-alpha , and IL-1beta. There was no change in the rectal temperature of the control or the Typhimurium-challenged pigs (compared with d 0) or when comparing Typhimurium-challenged pigs with control animals. In contrast, pigs fed Choleraesuis had increased rectal temperatures beginning on d 2 and continuing through d 7 (P < 0.05), with the greatest elevation on d 3 (P < 0.001) compared with the control pigs. Average daily gain and ADFI of pigs challenged with Typhimurium did not differ from those of the control animals. Pigs fed Choleraesuis had a 25% reduction in ADG (P < 0.0001) and ADFI (P < 0.002) compared with the control pigs. On d 7, pigs fed Choleraesuis had reduced serum IGF-I compared with control (P < 0.01) or Typhimurium-challenged pigs (P = 0.01). Bacterial feeding did not affect serum tumor necrosis factor-alpha or IL-1beta compared with control pigs at any time throughout the experiment. We conclude that repeated exposure of weaned pigs to Choleraesuis reduced growth performance in the absence of changes in systemic inflammatory cytokines.

Gene expression profiling in Salmonella Choleraesuis-infected porcine lung using a long oligonucleotide microarray

Understanding the transcriptional response to pathogenic bacterial infection within food animals is of fundamental and applied interest. To determine the transcriptional response to Salmonella enterica serovar Choleraesuis (SC) infection, a 13,297-oligonucleotide swine array was used to analyze RNA from control, 24-h postinoculation (hpi), and 48-hpi porcine lung tissue from pigs infected with SC. In total, 57 genes showed differential expression (p < 0.001; false discovery rate = 12%). Quantitative real-time PCR (qRT-PCR) of 61 genes was used to confirm the microarray results and to identify pathways responding to infection. Of the 33 genes identified by microarray analysis as differentially expressed, 23 were confirmed by qRT-PCR results. A novel finding was that two transglutaminase family genes (TGM1 and TGM3) showed dramatic increases in expression postinoculation; combined with several other apoptotic genes, they indicated the induction of apoptotic pathways during SC infection. A predominant T helper 1-type immune response occurred during infection, with interferon gamma (IFNG) significantly increased at 48 hpi. Genes induced by IFNs (GBP1, GBP2, C1S, C1R, MHC2TA, PSMB8, TAP1, TAP2) showed increased expression during porcine lung infection. These data represent the first thorough investigation of gene regulation pathways that control an important porcine respiratory and foodborne bacterial infection.

Novel attenuated Salmonella enterica serovar Choleraesuis strains as live vaccine candidates generated by signature-tagged mutagenesis

Salmonella enterica serovar Choleraesuis is a host-adapted pathogen that causes swine paratyphoid. Signature-tagged mutagenesis (STM) was used to understand the pathogenicity of S. enterica serovar Choleraesuis in its natural host and also to develop novel attenuated live vaccine candidates against this disease. A library of 960 signature-tagged mutants of S. enterica serovar Choleraesuis was constructed and screened for attenuation in pigs. Thirty-three mutants were identified by the STM screening, and these mutants were further screened for attenuation by in vivo and in vitro competitive growth. Of these, 20 mutants targeting the outer membrane, type III secretion, transporter, lipopolysaccharide biosynthesis, and other unknown proteins were confirmed for attenuation. Five highly attenuated mutants (SC2D2 [ssaV], SC4A9 [gifsy-1], SC6F9 [dgoT], SC12B12 [ssaJ], and SC10B1[spiA]) were selected and evaluated for safety and protective efficacy in pigs by comparison with a commercially available vaccine strain. STM-attenuated live vaccine strains SC4A9 (gifsy-1) and SC2D2 (ssaV) were superior to commercially available live vaccine because they provided both safety and a protective immune response against challenge in pigs.

Occurrence of Swine Salmonellosis in Postweaning Multisystemic Wasting Syndrome (PMWS) Affected Pigs Concurrently Infected with Porcine Reproduction and Respiratory Syndrome Virus (PRRSV)

Fourteen diseased pigs from four farms in which there had been an outbreak of salmonellosis were investigated. Granulomatous inflammation with depletion of lymphocytes was observed in the swollen lymph nodes in these pigs. Antigens to porcine circovirus type 2 (PCV2) were immunolabeled in the lesions along with detection of viral DNA as PCV2 by polymerase chain reaction (PCR). In addition, antigens to porcine reproductive respiratory syndrome virus (PRRSV) were immunodetected in the lungs and Salmonella Choleraesuis was isolated from the affected pigs. The nine salmonellosis affected pigs, five (55.6%) with salmonellosis and PMWS concurrently infected with PRRSV were much higher than those infected with salmonellosis and PMWS (22.2%) or with salmonellosis and PPPRV (22.2%).

Occurrence of Salmonella in the Ileum, Ileocolic Lymph Nodes, Tonsils, Mandibular Lymph Nodes and Carcasses of Pigs Slaughtered for Consumption

This study evaluates the occurrence of Salmonella in pork carcasses and in some risk tissues (ileum, ileocolic and mandibular lymph nodes and tonsils), that can be involved in Salmonella contamination during slaughter. Salmonella was identified in 27 (26.7%) pigs and in 13 (12.9%) carcasses. From these positive carcasses, 69.2% presented the same serotype as that identified in the corresponding pig, which emphasize the pigs importance as a source of Salmonella during the slaughter, suggesting that measures should be taken at the level of pig production in order to reduce the slaughtering of Salmonella-positive animals. The highest value of Salmonella occurrence was reached in the ileocolic lymph nodes (18.8%) and in the ileum (13.9%), representing Salmonella potential faecal source during pork processing at the abattoir. In these samples, a high level of Salmonella was observed in the ileocolic lymph nodes in comparison with the ileum. The mandibular lymph nodes (12.9%) also presented a higher occurrence in comparison with the tonsils (9.9%). These results indicate that the lymph nodes analysis could be more sensitive in the detection of Salmonella than the closer drainage tissue. Otherwise, the presence of Salmonella in the lymph nodes indicates lymphatic spread of the organism, which reflects an increased risk of pork contamination. These results also indicate that, in order to achieve a better control of Salmonella contamination during the slaughter process, it is important to consider the improvement of the evisceration practices and the tonsils as well the extraction of mandibular lymph nodes after slaughter.

Salmonella Epidemiology and Pathogenesis in Food-Producing Animals

This review reviews the pathogenesis of different phases of Salmonella infections. The nature of Salmonella infections in several domesticated animal species is described to highlight differences in the epidemiology and pathogenesis of salmonellosis in different hosts. The biology of Salmonella serovar host specificity is discussed in the context of our current understanding of the molecular basis of pathogenesis and the potential impact of different virulence determinants on Salmonella natural history. The ability to colonize the intestine, as evidenced by the shedding of relatively large numbers of bacteria in the feces over a long period, is shared unequally by Salmonella serovars. Studies probing the molecular basis of Salmonella intestinal colonization have been carried out by screening random transposon mutant banks of serovar Typhimurium in a range of avian and mammalian species. It is becoming increasingly clear that Salmonella pathogenicity island 2 (SPI2) is a major virulence factor during infection of food-producing animals, including cattle and poultry. The prevalence of Salmonella serovars in domestic fowl varies in different countries and with time. Although chickens are the natural hosts of serovars Gallinarum and Pullorum, natural outbreaks caused by these serovars in turkeys, guinea fowl, and other avian species have been described. There are two possible explanations to account for the apparent host specificity of certain Salmonella serovars. Environmental factors may increase exposure of particular animal species to certain serovars. Alternatively, there are genetic differences between these serovars, which allow them to survive and/or grow in specific niches only found within ruminants or pigs.

Distribution of salmonella strains in farrow-to-finish pig herds: a longitudinal study

The aims of this study were to investigate patterns of Salmonella shedding in finishing pigs and to study the role of the sow in the transmission of Salmonella to her offspring. In each of the three herds (A, B, and C), one cohort of sows (n = 34, n = 40, n = 32, respectively) together with three piglets of their offspring (n = 102, n = 120, n = 96, respectively) were selected. Individual fecal and blood samples were taken from the sows at different times during one production cycle and from the piglets from weaning until slaughter. At slaughter, contents from the jejunum, colon, and mesenteric lymph nodes were collected. Fecal samples, as well as the jejunum, colon, and mesenteric lymph node samples collected at slaughter, were submitted to a qualitative Salmonella analysis. Isolates were characterized by random amplified polymorphic DNA, and if necessary, further characterization was done by pulsed-field gel electrophoresis. In herds A and B, Salmonella shedding began in the nursery. A significant increase in the number of Salmonella shedders was seen after transferring pigs to the growing unit in herd B (P = 0.003) and to the finishing unit in herds A (P < 0.001) and B (P = 0.013). None of the fattening pigs in herd C were shedding Salmonella. This study reveals that transferring pigs is an important trigger to induce Salmonella shedding, leading to horizontal spread. Direct transmission of Salmonella from the sows to their piglets could not be demonstrated, but the similarities between the isolates found in the sows and those found during the nursery and finishing periods and at slaughter suggested indirect transmission.

The role of contaminated feed in the epidemiology and control of Salmonella enterica in pork production

Food animal producers have ethical obligations to reduce the risk of foodborne hazards in animals under their care. Contaminated feed is a recognized source of Salmonella infection of food animals and regulations to control Salmonella contamination of animal feed have existed in some countries for decades. The impact of reducing Salmonella contamination of animal feeds on the risk of human foodborne salmonellosis is difficult to assess, and is likely to vary among food animal industries. In the context of U.S. pork production, factors that may attenuate or negate the impact (on public health) of regulatory interventions to control Salmonella in commercial feed include widespread use of on-farm mixing of swine feed; incomplete decontamination of feed during processing; post-processing contamination of feed at feed mills or in transportation or on-farm storage; the multitude of nonfeed sources of Salmonella infection; an apparently high risk of post-farm infection in lairage; and post-harvest sources of contamination. A structured survey of the extent of Salmonella contamination of animal feed in the United States is necessary to enable more informed debate on the feasibility and likely efficacy of enforcing a Salmonella-negative standard for animal feeds to reduce the incidence of human salmonellosis.

Oral vaccination of pigs with an invasive gyrA-cpxA-rpoB Salmonella Typhimurium mutant

The potency to protect pigs against colonization and against clinical salmonellosis was evaluated after oral immunization with a live gyrA-cpxA-rpoB Salmonella (S.) Typhimurium mutant (S. Tm. Nal2/Rif9/Rtt). Twenty 4-week-old male hybrid piglets were immunized orally, a control group received a placebo. Three weeks postimmunization, all pigs were challenged orally with a highly virulent S. Typhimurium DT104 strain. Clinical investigation revealed that immunization prevented the vaccinated pigs from clinical symptoms of salmonellosis. While all placebo-treated animals showed a 2-4-day episode of moderate to severe clinical symptoms, 90% of immunized pigs did not show any clinical signs at all. The bacteriological results showed a marked beneficial effect of the oral immunization. Vaccinated pigs showed a significantly decreased rate of colonization of the inner organs (42.5% versus 87.5%) when compared to the placebo-treated animals. Furthermore, in comparison to the non-immunized pigs, the vaccines developed a higher specific immunoglobulin (Ig)A antibody activity, but a significant lower IgM antibody activity in serum. The findings underline the ability of an attenuated oral live S. Typhimurium mutant to prevent clinical symptoms of salmonellosis in pigs and to significantly reduce the colonization of tissues and inner organs, as well as the shedding of S. Typhimurium.

A mathematical model for the transmission of Salmonella Typhimurium within a grower-finisher pig herd in Great Britain

In a study of pigs slaughtered at British abattoirs, approximately 23% carried Salmonella in their cecal (large intestine) contents. The most frequent serotype was Salmonella Typhimurium (STM), which was the second most common cause of human salmonellosis in Great Britain. A pig industry-monitoring program was developed to reduce Salmonella infection on British farms. The control of STM infection on the farm requires an understanding of STM transmission dynamics within the herd, and a mathematical model has been developed for an infected grower-finisher farm. The model estimates the probability of a random pig being infected with STM. There are three broad categories of STM infection in pigs: pigs that are infected but unable to transmit the infection (latent); pigs that are infectious, i.e., able to transmit the infection (shedders); and pigs that have stopped shedding but harbor STM in their internal organs (carriers). The model estimates that 21.0% (5th and 95th percentiles, 0.05 to 77.5%) of slaughter-age pigs on an infected farm are likely to be shedding STM. Although this range is wide, it is biologically plausible. Sensitivity analysis of the total number of infected pigs revealed that the most significant input parameters are the probability of effective contact between a specific infectious and susceptible pig and the duration of shedding. The model predicted that 11.5% of pigs would be shedding STM at slaughter age. This value is close to the estimate obtained from a British abattoir survey that 11. 1% of pigs carried STM in their ceca, indicating that the model has reasonable validity.

Protective efficacy of IgA monoclonal antibodies to O and H antigens in a mouse model of intranasal challenge with Salmonella enterica serotype Enteritidis

Protective properties of immunoglobulin A (IgA) monoclonal antibodies (MAbs) directed against O and H antigens of Salmonella enterica serotype Enteritidis (S. enteritidis) were evaluated in a model of generalized infection after intranasal (i.n.) inoculation of BALB/c mice. Passive i.n. instillation of antibodies 1 h before i.n. challenge did not prevent infection, and mice developed rapid inflammatory response in the lower respiratory tract. The passive systemic immunization was partially protective and a single intravenous (i.v.) injection of both O and H antigen specific IgA antibodies prolonged survival period of the infected animals. Permanent secretion of O:9 specific IgA MAb 177E6 into the respiratory tract in a "backpack" tumor model protected 50% of animals infected i.n. with a high dose of virulent S. enteritidis strain. Thus, secretory IgA (S-IgA) directed against O:9 antigen alone can prevent bacterial invasion in the respiratory epithelium.

Salmonella enterica serotype Choleraesuis: epidemiology, pathogenesis, clinical disease, and treatment

Nontyphoid Salmonella strains are important causes of reportable food-borne infection. Among more than 2,000 serotypes, Salmonella enterica serotype Choleraesuis shows the highest predilection to cause systemic infections in humans. The most feared complication of serotype Cholearesuis bacteremia in adults is the development of mycotic aneurysm, which previously was almost uniformally fatal. The advances in diagnostic techniques, surgical care, and antimicrobial therapy have greatly improved the survival of these patients. However, the recent emergence of serotype Choleraesuis that is resistant to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and, notably, fluoroquinolone antibiotics has aroused concern about the use of these agents for the empirical treatment of systemic infection caused by this organism. In view of the serious implications of the situation, the chain of transmission and mechanism of resistance should be carefully studied to reduce the spread of infection and threat to human health. To date, there are no vaccines available to prevent serotype Choleraesuis infections in humans. The availability, in the near future, of the genome sequence of serotype Cholearesuis will facilitate the development of effective vaccines as well as the discovery of new targets for novel antimicrobial agents.

Enrichment for isolating Salmonella Choleraesuis and other Salmonella spp. from pigs

The growth of Salmonella Choleraesuis was examined in Rappaport Vassiliadis broth (RV) and Hajna-tetrathionate broth (HTT) at 37 and 42 degrees C. As the enrichment in RV at 37 degrees C was satisfactory for isolating S. Choleraesuis, we used this enrichment for isolation from the samples collected from 15 asymptomatic pigs reared on a S. Choleraesuis contaminated farm. S. Choleraesuis was frequently isolated from six pigs (40.0%) under field conditions. The isolation of other Salmonella serovars than S. Choleraesuis was attempted by using both RV enrichment at 37 degrees C and HTT enrichment at 42 degrees C. Salmonella organisms were isolated from 156 (44.8%) of 348 fecal samples and more frequently with HTT at 42 degrees C (43.4%) than with RV at 37 degrees C (20.9%). If other serovars in addition to S. Choleraesuis are to be surveyed, HTT enrichment should be used in combination with RV enrichment.

Analysis of Salmonella enterica serotype-host specificity in calves: avirulence of S. enterica serotype gallinarum correlates with bacterial dissemination from mesenteric lymph nodes and persistence in vivo

Host and bacterial factors that determine whether Salmonella serotypes remain restricted to the gastrointestinal tract or penetrate beyond the mucosa and cause systemic disease remain largely undefined. Here, factors influencing Salmonella host specificity in calves were assessed by characterizing the pathogenesis of different serotypes. Salmonella enterica serotype Dublin was highly virulent intravenously, whereas S. enterica serotype Choleraesuis was moderately virulent. Both serotypes were virulent in calves infected orally. In contrast, S. enterica serotypes Gallinarum and Abortusovis were avirulent by either route. Serotypes Dublin, Gallinarum, and Abortusovis colonized the intestinal tract 24 h after oral inoculation, yet only serotype Dublin was consistently recovered from systemic tissues. Serotypes Dublin and Gallinarum invaded bovine intestines in greater numbers and induced greater enteropathogenic responses than serotypes Choleraesuis and Abortusovis. However, only serotype Dublin was able to persist within the intestinal mucosa, and use of a novel cannulation model demonstrated that serotype Dublin was able to pass through the mesenteric lymph nodes in greater numbers than serotype Gallinarum. Together, these results suggest that initial interactions with the intestinal mucosa do not correlate with host specificity, although persistence within tissues and translocation via efferent lymphatics appear to be crucial for the induction of bovine salmonellosis.

Characterisation of a resource population of pigs screened for resistance to salmonellosis

The degree of resistance to Salmonella choleraesuis infection in a reference family purposely bred to map resistance genes was assessed. Aspects of the innate and specific immune system were studied to find a parameter that might predict the resistance of pigs to salmonellosis. The family was bred from commercial full-sister pairs of F1-gilts and four boars. One boar (G398) was identified as breeding susceptible offspring, and one boar (G402) as breeding resistant offspring on the basis of pyrexial responses and numbers of Salmonella in liver and spleen post mortem. The other two boars were classified as 'possible resistant' (Y2008) and 'unknown' (Y6101) respectively. Functional differences in immune cells (neutrophils and lymphocytes) between the offspring of G398 and G402 were detected. The most resistant piglets had a higher number of circulating neutrophils and better polymorphonuclear neutrophils (PMNs) function, but a lower mitogenic response of lymphocytes both pre- and post-infection and a lower antibody response. Between the offspring groups of Y2008 and Y6101 no differences were found in the number of viable Salmonella in liver and spleen at post mortem or in immune cell function, however, the survival rate of these offspring groups was clearly different. Twenty three percent of the Y2008-offspring and 33% of the Y6101-offspring reached the predetermined humane clinical endpoint before the end of the experiment. Our findings suggest a role for several inherited immunological traits, including PMN function and lecithin-induced mitogenic proliferation, which appear to influence resistance to salmonellosis.

Antimicrobial use and resistance in animals

Food animals in the United States are often exposed to antimicrobials to treat and prevent infectious disease or to promote growth. Many of these antimicrobials are identical to or closely resemble drugs used in humans. Precise figures for the quantity of antimicrobials used in animals are not publicly available in the United States, and estimates vary widely. Antimicrobial resistance has emerged in zoonotic enteropathogens (e.g., Salmonella spp., Campylobacter spp.), commensal bacteria (e.g., Escherichia coli, enterococci), and bacterial pathogens of animals (e.g., Pasteurella, Actinobacillus spp.), but the prevalence of resistance varies. Antimicrobial resistance emerges from the use of antimicrobials in animals and the subsequent transfer of resistance genes and bacteria among animals and animal products and the environment. To slow the development of resistance, some countries have restricted antimicrobial use in feed, and some groups advocate similar measures in the United States. Alternatives to growth-promoting and prophylactic uses of antimicrobials in agriculture include improved management practices, wider use of vaccines, and introduction of probiotics. Monitoring programs, prudent use guidelines, and educational campaigns provide approaches to minimize the further development of antimicrobial resistance.