Lawsonia intracellularis: getting inside the pathogenesis of proliferative enteropathy

Lawsonia intracellularis regulates nuclear factor-κB signalling pathway during infection

Lawsonia intracellularis is the etiological agent of proliferative enteropathy (PE) in pigs, horses and wide range of mammals. Little is known about the role of innate immune response during L. intracellularis infection. In this study, we investigated the nuclear factor-κB (NF-κB)-regulated immune response against infection of a clinical strain Dkp23 and a live-attenuated Enterisol vaccine strain in PK-15 cells. We found that expression of NF-κB target genes TNF-α, IFN-γ, IL-6 and IL-8 were modulated during the course of infection. At 5 dpi, there was a significant increase in p65 NF-κB activation, including protein nuclear translocation and phosphorylation, synchronous with the induction of IL-6, IFN-γ and IL-8 expression in L. intracellularis infected cells, especially for Enterisol vaccine strain-infected cells. This result suggests that NF-κB signalling level is induced when L. intracellularis bacterial load peaks at 5 dpi. The induction of pro-inflammatory cytokines expression is consistent with the decreased viability of L. intracellularis-infected cells especially that of the vaccine strain. There were no significant changes in NF-κB signalling between vaccine and Dkp23 infection in PK-15 cells, except for moderate levels of differences in NF-κB target genes expression which might be a reflection of differences in intracellular bacterial load. Overall, the data presented here indicate a correlation between the induction of NF-κB signalling and the L. intracellularis bacterial load in PK-15 cells.

High Seroprevalence of Lawsonia intracellularis in Thoroughbred Farms in Southern Brazil

The aim of the present study was to carry out a serological survey to identify the seroprevalence of Lawsonia intracellularis in six Thoroughbred farms in the Southern region of the state of Rio Grande do Sul, Brazil. During 2019 and 2020, blood samples from 686 Thoroughbred horses were obtained from six different breeding farms. Horses were divided into groups according to age: (1) broodmares (>5 years), (2) two-year-old foals, (3) yearlings, and (4) 0-6 months-old foals. Blood samples were collected by venipuncture of the external jugular vein. The detection of antibodies (IgG) against L. intracellularis was performed by Immunoperoxidase Monolayer Assay. The detection of specific antibodies (IgG) against L. intracellularis in the evaluated population was 51%. The highest detection (86.8%) of IgG was in the broodmares category, while the lowest (5.2%) was in foals of 0-6 months of age. Regarding the farms, the Farm 1 had the highest (67.4%) prevalence of seropositivity against L. intracellularis, while Farm 4 had the lowest (30.6%). There was no record of clinical manifestation of Equine Proliferative Enteropathy in the sampled animals. The results of this study show the high seroprevalence of L. intracellularis in Thoroughbred farms in the Southern of Rio Grande do Sul, suggesting a large and continuous exposure to the agent.

Alleviative Effect of Probiotic Ferment on Lawsonia intracellularis Infection in Piglets

(1) Background: Lawsonia intracellularis (LI) is an obligate intracellular Gram-negative bacterium that causes porcine ileitis. Pigs infected with LI have severe ileal lesions and show symptoms of diarrhea, indigestion, and growth retardation. Previous studies found that probiotic ferment (FAM) improved the growth performance, gut barrier, and function in piglets. Therefore, we aimed to reveal the mechanism that FAM alleviates negative performance in LI-challenged piglets by characterizing the changes in intestinal integrity, function, and gut microbiota following FAM supplementation. (2) Methods: Twenty-four healthy piglets were randomly allotted to four treatments. Three groups were challenged with LI; both FAM addition and vaccination were performed to explore their positive effects on LI-infected piglets. (3) Results: Piglets infected with LI showed lower growth performance and typical pathological symptoms. Moreover, microscopic images showed that observed intestinal morphological damage could be repaired by FAM and vaccine. To explore the digestion of nutrients in piglets, both digestive enzyme activity and ileal transporter expression were performed to reveal the promoting effect of additives. Reduction of LI colonization intervention by FAM could also ameliorate abnormal differentiation and function of intestinal epithelial cells and alleviate severe inflammatory responses in piglets. Regarding the gut microbiota, both the structure and function of the ileal and colonic microbiota were altered following FAM supplementation. (4) Conclusions: In conclusion, probiotic ferment can reduce the colonization of LI in the ileum, improve intestinal damage, barrier function and microbiota structure, and enhance digestive enzyme activity and nutrient transport proteins expression, thereby improving piglet growth performance, which has the effect of preventing ileitis in pigs.

Prebiotics and β-Glucan as gut modifier feed additives in modulation of growth performance, protein utilization status and dry matter and lactose digestibility in weanling pigs

There are growing interests in developing novel gut modifier feed additives and alternative therapeutics to replace antimicrobials to enhance efficiency of nutrient utilization and to address the antimicrobial resistance threat to public health facing the global pork production. Biological mechanisms of supplementing lactose for enhancing weanling pig growth and nitrogen utilization are unclear. Thus, this study was prompted to determine effects of dietary supplementation of 3 prebiotics and oat β-glucan vs. a sub-therapeutic antibiotic on growth performance, whole-body protein utilization status, the apparent total tract dry matter (DM) and lactose digestibility in weanling pigs fed corn and soybean meal (SBM)-based diets. Six experimental diets were formulated with corn (40%), SBM (28%) and supplemented with dried whey powder (20%) and fish meal (9%) with titanium oxide (0.30%) as the digestibility marker. Diet 1 (NC, negative control), as the basal diet, contained no antibiotics and no supplemental prebiotics or β-glucan. Diet 2 (PC, positive control), contained an antibiotic premix (Lincomix-44 at 0.10%) in the basal diet at the expense of cornstarch. Diets 3, 5 and 6 contained 0.75% of the three test prebiotics of retrograded cornstarch (Diet 3), Fibersol-2 (Diet 5, a modified digestion-resistant maltodextrin) and inulin (Diet 6), and the viscous soluble fiber oat β-glucan (Diet 4), respectively, at the expense of cornstarch. A total of 144 Yorkshire pigs, at the age of 21 days (d) and an average body weight (BW) of 5.5 kg, were allocated to 12 floor pens with 3 barrows and 3 gilts per pen, and fed one of the 6 diets for 21 d in 2 study blocks according to a completely randomized block design. Initial and final pig BW, average daily gain (ADG), average daily feed intake (ADFI), representative pig plasma urea concentration as well as the apparent total tract DM and lactose digestibility during d 8-15 were measured. Analyses of variances, Dunnett’s and Tukey’s tests were conducted on the endpoints by using the SAS mixed model. There were no differences (P > 0.05) in ADG, ADFI, feed to gain ratio, plasma urea concentration, the apparent total tract apparent DM and lactose digestibility and the predicted whole-gut lactase digestive capacity among the diets, as examined by the Tukey’s test. There were no differences (P > 0.05) in these endpoints between each of the four treatment diets and the NC or the PC diet as examined by the Dunnett’s test. The total tract lactose digestibility was determined to be at 100%. The predicted whole-gut lactase digestive capacity was about eight times of the daily lactose intake when dietary lactose contents were supplemented at 10 - 12% (as-fed basis). In conclusion, dietary supplementation (at 0.75%) of the prebiotics and the oat β-glucan did not significantly affect the major growth performance endpoints, whole-body protein utilization status as well as the apparent total tract DM and lactose digestibility in the weanling pigs fed the corn and SBM-based diets. The promoting effect for growth and nitrogen utilization associated with dietary supplementation of lactose is due to the fact that lactose is a completely and rapidly digestible sugar rather than acting as an effective prebiotic in weanling pig nutrition.

Evaluation of host and bacterial gene modulation during Lawsonia intracellularis infection in immunocompetent C57BL/6 mouse model

BACKGROUND

Proliferative enteritis caused by Lawsonia intracellularis undermines the economic stability of the swine industry worldwide. The development of cost-effective animal models to study the pathophysiology of the disease will help develop strategies to counter this bacterium.

OBJECTIVES

This study focused on establishing a model of gastrointestinal (GI) infection of L. intracellularis in C57BL/6 mice to evaluate the disease progression and lesions of proliferative enteropathy (PE) in murine GI tissue.

METHODS

We assessed the murine mucosal and cell-mediated immune responses generated in response to inoculation with L. intracellularis.

RESULTS

The mice developed characteristic lesions of the disease and shed L. intracellularis in the feces following oral inoculation with 5 × l07 bacteria. An increase in L. intracellularis 16s rRNA and groEL copies in the intestine of infected mice indicated intestinal dissemination of the bacteria. The C57BL/6 mice appeared capable of modulating humoral and cell-mediated immune responses to L. intracellularis infection. Notably, the expression of genes for the vitamin B12 receptor and for secreted and membrane-bound mucins were downregulated in L. intracellularis -infected mice. Furthermore, L. intracellularis colonization of the mouse intestine was confirmed by the immunohistochemistry and western blot analyses.

CONCLUSIONS

This is the first study demonstrating the contributions of bacterial chaperonin and host nutrient genes to PE using an immunocompetent mouse model. This mouse infection model may serve as a platform from which to study L. intracellularis infection and develop potential vaccination and therapeutic strategies to treat PE.

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

High Seroprevalence Against Lawsonia intracellularis Among Adult Horses in Belgium

Lawsonia intracellularis (LI) is an obligate intracellular gram-negative rod causing equine proliferative enteropathy (EPE). Occasional cases of EPE have been reported in foals living in Belgium, but the seroprevalence of equine LI in this country is unknown. The target population included clinically healthy adult horses, whose blood samples were collected and analyzed for specific IgG antibodies against LI using a blocking enzyme-linked immunosorbent assay test. The results were expressed as percentage of inhibition (PI). Samples that had a PI <20% were judged as negative, those between 20 and 30% as inconclusive, and those >30% were considered positive. A total of 356 blood samples were analyzed with 352 horses (98.8%) testing positive, 2 horses (0.6%) testing negative, and 2 horses (0.6%) showing inconclusive results. The large percentage of seropositive samples obtained in this study confirms a widespread exposure of Belgian horses to LI.

Survival of Lawsonia intracellularis in porcine peripheral blood monocyte-derived macrophages

Lawsonia intracellularis, an obligately intracellular enteric bacterium, infects intestinal epithelial cells, but may also be found within macrophages in the intestinal lamina propria of affected pigs. Macrophages play an important role in host defense against infectious agents, but the role of this cell in L. intracellularis infection is not well understood. The aim of this study was to evaluate the permissibility of macrophages to L. intracellularis infection in vitro. Pure culture of L. intracellularis was added to swine peripheral blood monocyte-derived macrophages. Viability of intracytoplasmic L. intracellularis was evaluated at different time points by transmission electron microscopy (TEM). Potential replication of L. intracellularis in macrophages was also evaluated by qPCR. By TEM, phagocytosis L. intracellularis within of phagolysosomes were observed 1-hour post-infection (hpi) and bacterial structures in binary fission at 48 hpi. The number of intracellular bacteria was determined at 1, 4, 24, 48, and 72 hpi by qPCR in infected macrophages and compared to the number of intracellular bacteria from culture in McCoy cells. In both cell lines, the amount of L. intracellularis was decreased at 4 hpiand increased at 24 hpi. The number of intracellular bacteria continued to increase in McCoy cells over time. This is the first study showing interaction, survival and propagation of L. intracellularis in macrophages. These findings are critical to establish an experimental model for future studies of the pathogenesis of porcine proliferative enteropathy and the potential persistence of L. intracellularis in macrophages during chronic infections.

The Effects of a Phytogenic Additive on the Histomorphometric Characteristics of the Intestines in Weaned Pigs with a Subclinical Natural Infection with Lawsonia intracellularis

Proliferative enteropathy, also known as proliferative ileitis, is considered to be one of the most economically important diseases in pig production worldwide. The estimated losses per affected growing pig usually range from US $1 to $5. The disease is caused by Lawsonia intracellularis, a Gram-negative, obligately intracellular bacterium. Control of the disease can be achieved with the use of vaccines or antibiotics. Recently there has been an increase in the efforts in the control of certain pathologies of the digestive system with phytogenic additives. The aim of this work was to assess the effects of a phytogenic additive on the histomorphometric characteristics of the intestines in weaned pigs with a subclinical infection with L. intracellularis acquired spontaneously. Histomorphometry analysis showed that crypt depth was significantly shorter (P<0.05), and the villus-height-to-crypt-depth ratio (P<0.05) significantly greater in the treatment group than the control. This improvement in the histological parameters of the intestine, considered to be indicators of its health, proved the positive effect of the tested additive on the digestive system in pigs.

Physiological and gut microbiome changes associated with low dietary protein level in genetically improved farmed tilapia (GIFT, Oreochromis niloticus) determined by 16S rRNA sequence analysis

The aim of this study was to determine the effects of different dietary protein levels on the growth, physiological parameters, and gut microbiome of genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Two pellet feed diets with low (25%, LPD) and normal (35%, NPD) protein levels were fed to GIFT in aquaria at 28°C for 8 weeks. The LPD reduced trypsin activity and inhibited the growth of GIFT. The serum alanine amino transferase and aspartate transaminase activities, hepatic malondialdehyde content, and superoxide dismutase, glutathione peroxidase, and catalase activities were significantly higher in LPD GIFT than in NPD GIFT (p < .05). The LPD led to decreased lysozyme activity and increased levels of C3 (p < .05). A 16S rRNA gene profiling analysis showed that the LPD significantly affected the gut microbial composition. Compared with the NPD, the LPD significantly decreased intestinal microbial diversity (p < .05). The macronutrient distribution affected the taxonomic profile of gut bacteria, mainly the phyla Bacteroidetes, Proteobacteria, and Firmicutes. The LPD favored growth of the genus Bacteroides. The NPD appeared to increase the abundance of the genera Lawsonia, Romboutsia, and Sphingomonas. Our results showed that, compared with NPD GIFT, the LPD GIFT had weakened nonspecific immune function, altered microbial community structure, and decreased gut microbial diversity.

Wnt/β-Catenin Signaling as a Molecular Target by Pathogenic Bacteria

The Wnt/β-catenin signaling pathway is crucial to regulate cell proliferation and polarity, cell determination, and tissue homeostasis. The activation of Wnt/β-catenin signaling is based on the interaction between Wnt glycoproteins and seven transmembrane receptors-Frizzled (Fzd). This binding promotes recruitment of the scaffolding protein Disheveled (Dvl), which results in the phosphorylation of the co-receptor LRP5/6. The resultant molecular complex Wnt-Fzd-LRP5/6-Dvl forms a structural region for Axin interaction that disrupts Axin-mediated phosphorylation/degradation of the transcriptional co-activator β-catenin, thereby allowing it to stabilize and accumulate in the nucleus where it activates the expression of Wnt-dependent genes. Due to the prominent physiological function, the Wnt/β-catenin signaling must be strictly controlled because its dysregulation, which is caused by different stimuli, may lead to alterations in cell proliferation, apoptosis, and inflammation-associated cancer. The virulence factors from pathogenic bacteria such as Salmonella enterica sv Typhimurium, Helicobacter pylori, Mycobacterium tuberculosis, Pseudomonas aeruginosa, Citrobacter rodentium, Clostridium difficile, Bacteroides fragilis, Escherichia coli, Haemophilus parasuis, Lawsonia intracellularis, Shigella dysenteriae, and Staphylococcus epidermidis employ a variety of molecular strategies to alter the appropriate functioning of diverse signaling pathways. Among these, Wnt/β-catenin has recently emerged as an important target of several virulence factors produced by bacteria. The mechanisms used by these factors to interfere with the activity of Wnt/β-catenin is diverse and include the repression of Wnt inhibitors' expression by the epigenetic modification of histones, blocking Wnt-Fzd ligand binding, activation or inhibition of β-catenin nuclear translocation, down- or up-regulation of Wnt family members, and inhibition of Axin-1 expression that promotes β-catenin activity. Such a variety of mechanisms illustrate an evolutionary co-adaptation of eukaryotic molecular signaling to a battery of soluble or structural components synthesized by pathogenic bacteria. This review gathers the recent efforts to elucidate the mechanistic details through which bacterial virulence factors modulate Wnt/β-catenin signaling and its physiological consequences concerning the inflammatory response and cancer.

Draft Genome Sequences of Lawsonia intracellularis Swine Strains Causing Proliferative Enteropathy in Japan

The draft genome sequences of three strains of Lawsonia intracellularis, an obligate intracellular animal pathogen responsible for causing proliferative enteropathy, obtained from swine in different prefectures in Japan revealed the absence of a genomic island previously reported to be linked to host adaptation and to high genomic diversity, despite geographical proximity.

The draft genome sequences of three strains of Lawsonia intracellularis, an obligate intracellular animal pathogen responsible for causing proliferative enteropathy, obtained from swine in different prefectures in Japan revealed the absence of a genomic island previously reported to be linked to host adaptation and to high genomic diversity, despite geographical proximity.

Ex vivo penetration of fosfomycin into healthy and Lawsonia intracellularis-colonized swine intestinal mucosa

Fosfomycin (FOS) is an antibiotic used, mostly in Latin America, for the treatment of lung and enteric infections of pigs. Intracellular fluids of enterocytes can act as biophase for Lawsonia intracellularis, the causative agent of porcine proliferative enteropathy (PPE). The aim of this study was to determine whether the presence of L. intracellularis in the enterocytes modifies FOS penetration. Eight healthy pigs in growth-finishing stage were used to produce healthy (group A) and L. intracellularis-colonized (group B) intestinal explants. For both groups, treatment consisted of a 580 μg/ml concentration of calcium FOS, which was added to each explant (0.5-6 hr). For group B, the Enterisol Ileitis^® vaccine was used as source of the micro-organism. Previously to the assay, the time necessary for L. intracellularis to colonize the enterocytes was defined. Also, a PCR protocol was optimized to determine the presence of the pathogen in the explants. There were nonstatistical differences for the penetration of the antibiotic into healthy and L. intracellularis-colonized enterocytes. MIC₉₀ of FOS for L. intracellularis is unknown; nevertheless, MIC₉₀ of various antibiotics ranges between 0.125 and 128 μg/ml. FOS reaches inside the enterocyte concentrations which surpass the MICs₉₀ of other antibiotics that also act by the inhibition of cell wall synthesis; however, further studies should be carried out to determine fosfomycin MIC₉₀ for L. intracellularis to discern the usefulness of this antibiotic in the treatment of PPE.

Influence of phytogenic feed additive on Lawsonia intracellularis infection in pigs

Lawsonia intracellularis is known to cause proliferative enteropathy (PE), one of the economically most important swine diseases with global distribution. Not unlike other enteric diseases, PE is a frequent indication for antibiotic therapy. However, their unjustified use leads to an emerging problem - antimicrobial resistance. Thus, the aim of this research was to assess if a phytogenic additive may replace antibiotics in the control of PE in 144 weaned piglets (72 treated and 72 controls) naturally infected with L. intracellularis. The quantity of L. intracellularis faecal shedding was monitored by real-time polymerase chain reaction (PCR) assay in faecal samples on day 0, 14 and 28, whilst the level of the ileum damage was determined by immunohistochemistry (IHC) assay performed on gut sections. Real-time PCR assay revealed that cycle-threshold (Ct) values in the treatment group increased significantly over time and were higher than in the control. These results indicate that the use of the phytogenic additive decreases the faecal excretion of L. intracellularis both throughout the experiment and in comparison to the control. The expression of the L. intracellularis antigen in IHC assay was lower in treated animals, implying that the additive leads to the decrease in the pathogen quantity in the ileum. Significantly higher feed conversion ratio was recorded in the treatment group. The results indicate that the phytogenic additive may be beneficial in the control of PE, but additional research is necessary to assess its use in various pig categories and define the optimum concentrations.

Draft Genome Sequence of a Strain of Bacillus intestinalis sp. nov., a New Member of Sporobiota Isolated from the Small Intestine of a Single Patient with Intestinal Cancer

We report here the draft genome sequence of Bacillus intestinalis strain 1731, a novel spore-forming bacterium isolated from the small intestine of a patient with intestinal cancer. The genome comprised 4,047,276 bp, with 43.9% G+C content. There were 3,913 predicted protein-coding genes, including those associated with antibiotic resistance and virulence.

Lawsonia intracellularis exploits β-catenin/Wnt and Notch signalling pathways during infection of intestinal crypt to alter cell homeostasis and promote cell proliferation

Lawsonia intracellularis is an obligate intracellular bacterial pathogen that causes proliferative enteropathy (PE) in pigs. L. intracellularis infection causes extensive intestinal crypt cell proliferation and inhibits secretory and absorptive cell differentiation. However, the affected host upstream cellular pathways leading to PE are still unknown. β-catenin/Wnt signalling is essential in maintaining intestinal stem cell (ISC) proliferation and self-renewal capacity, while Notch signalling governs differentiation of secretory and absorptive lineage specification. Therefore, in this report we used immunofluorescence (IF) and quantitative reverse transcriptase PCR (RTqPCR) to examine β-catenin/Wnt and Notch-1 signalling levels in uninfected and L. intracellularis infected pig ileums at 3, 7, 14, 21 and 28 days post challenge (dpc). We found that while the significant increase in Ki67+ nuclei in crypts at the peak of L. intracellularis infection suggested enhanced cell proliferation, the expression of c-MYC and ASCL2, promoters of cell growth and ISC proliferation respectively, was down-regulated. Peak infection also coincided with enhanced cytosolic and membrane-associated β-catenin staining and induction of AXIN2 and SOX9 transcripts, both encoding negative regulators of β-catenin/Wnt signalling and suggesting a potential alteration to β-catenin/Wnt signalling levels, with differential regulation of the expression of its target genes. We found that induction of HES1 and OLFM4 and the down-regulation of ATOH1 transcript levels was consistent with the increased Notch-1 signalling in crypts at the peak of infection. Interestingly, the significant down-regulation of ATOH1 transcript levels coincided with the depletion of MUC2 expression at 14 dpc, consistent with the role of ATOH1 in promoting goblet cell maturation. The lack of significant change to LGR5 transcript levels at the peak of infection suggested that the crypt hyperplasia was not due to the expansion of ISC population. Overall, simultaneous induction of Notch-1 signalling and the attenuation of β-catenin/Wnt pathway appear to be associated with the inhibition of goblet cell maturation and enhanced crypt cell proliferation at the peak of L. intracellularis infection. Moreover, the apparent differential regulation of apoptosis between crypt and lumen cells together with the strong induction of Notch-1 signalling and the enhanced SOX9 expression along crypts 14 dpc suggest an expansion of actively dividing transit amplifying and/or absorptive progenitor cells and provide a potential basis for understanding the development and maintenance of PE.

Lawsonia intracellularis infection of intestinal crypt cells is associated with specific depletion of secreted MUC2 in goblet cells

The expression patterns of secreted (MUC2 and MUC5AC) and membrane-tethered (MUC1, MUC4, MUC12 and MUC13) mucins were monitored in healthy pigs and pigs challenged orally with Lawsonia intracellularis. These results showed that the regulation of mucin gene expression is distinctive along the GI tract of the healthy pig, and may reflect an association between the function of the mucin subtypes and different physiological demands at various sites. We identified a specific depletion of secreted MUC2 from goblet cells in infected pigs that correlated with the increased level of intracellular bacteria in crypt cells. We concluded that L. intracellularis may influence MUC2 production, thereby altering the mucus barrier and enabling cellular invasion.

Biology and Diseases of Rabbits

Beginning in 1931, an inbred rabbit colony was developed at the Phipps Institute for the Study, Treatment and Prevention of Tuberculosis at the University of Pennsylvania. This colony was used to study natural resistance to infection with tuberculosis (Robertson et al., 1966). Other inbred colonies or well-defined breeding colonies were also developed at the University of Illinois College of Medicine Center for Genetics, the Laboratories of the International Health Division of The Rockefeller Foundation, the University of Utrecht in the Netherlands, and Jackson Laboratories. These colonies were moved or closed in the years to follow. Since 1973, the U.S. Department of Agriculture has reported the total number of certain species of animals used by registered research facilities (1997). In 1973, 447,570 rabbits were used in research. There has been an overall decrease in numbers of rabbits used. This decreasing trend started in the mid-1990s. In 2010, 210,172 rabbits were used in research. Despite the overall drop in the number used in research, the rabbit is still a valuable model and tool for many disciplines.

Serum folate, cobalamin, homocysteine and methylmalonic acid concentrations in pigs with acute, chronic or subclinical Lawsonia intracellularis infection

Lawsonia intracellularis is the causative agent of porcine proliferative enteropathy. The clinical presentation can be acute (i.e. proliferative hemorrhagic enteropathy, PHE), chronic (i.e. porcine intestinal adenomatosis, PIA) or subclinical. In humans with chronic enteropathies, low serum folate (vitamin B(9)) and cobalamin (vitamin B(12)) concentrations have been associated with increased serum concentrations of homocysteine and methylmalonic acid (MMA), which reflect the availability of both vitamins at the cellular level. The aim of this study was to evaluate serum folate, cobalamin, homocysteine and MMA concentrations in serum samples from pigs with PHE, PIA or subclinical L. intracellularis infection, and in negative controls. Serum folate, cobalamin, homocysteine and MMA concentrations differed significantly among pigs in the PHE, PIA, subclinical and negative control groups. Serum folate concentrations in the PHE and PIA groups were lower than in the subclinical and negative control groups, while serum cobalamin concentrations were lower in the PIA group than in other groups. Serum concentrations of homocysteine were higher in the PHE, PIA and subclinical groups than in the negative control group. Serum concentrations of MMA were higher in the subclinical and PIA groups than in the control group. These data suggest that pigs infected with L. intracellularis have altered serum cobalamin, folate, homocysteine and MMA concentrations.

Recent Advances in Understanding the Pathogenesis of Lawsonia intracellularis Infections

Proliferative enteropathy is an infectious disease caused by an obligate intracellular bacterium, Lawsonia intracellularis, and characterized by thickening of the intestinal epithelium due to enterocyte proliferation. The disease is endemic in swine herds and has been occasionally reported in various other species. Furthermore, outbreaks among foals began to be reported on breeding farms worldwide within the past 5 years. Cell proliferation is directly associated with bacterial infection and replication in the intestinal epithelium. As a result, mild to severe diarrhea is the major clinical sign described in infected animals. The dynamics of L. intracellularis infection in vitro and in vivo have been well characterized, but little is known about the genetic basis for the pathogenesis or ecology of this organism. The present review focuses on the recent advances regarding the pathogenesis and host-pathogen interaction of L. intracellularis infections.

Laser microdissection coupled with RNA-seq analysis of porcine enterocytes infected with an obligate intracellular pathogen (Lawsonia intracellularis)

BACKGROUND

Lawsonia intracellularis is an obligate intracellular bacterium and the etiologic agent of proliferative enteropathy. The disease is endemic in pigs, emerging in horses and has been described in various other species including nonhuman primates. Cell proliferation is associated with bacterial replication in enterocyte cytoplasm, but the molecular basis of the host-pathogen interaction is unknown. We used laser capture microdissection coupled with RNA-seq technology to characterize the transcriptional responses of infected enterocytes and the host-pathogen interaction.

RESULTS

Proliferative enterocytes was associated with activation of transcription, protein biosynthesis and genes acting on the G1 phase of the host cell cycle (Rho family). The lack of differentiation in infected enterocytes was demonstrated by the repression of membrane transporters related to nutrient acquisition. The activation of the copper uptake transporter by infected enterocytes was associated with high expression of the Zn/Cu superoxide dismutase by L. intracellularis. This suggests that the intracellular bacteria incorporate intracytoplasmic copper and express a sophisticated mechanism to cope with oxidative stress.

CONCLUSIONS

The feasibility of coupling microdissection and RNA-seq was demonstrated by characterizing the host-bacterial interactions from a specific cell type in a heterogeneous tissue. High expression of L. intracellularis genes encoding hypothetical proteins and activation of host Rho genes infers the role of unrecognized bacterial cyclomodulins in the pathogenesis of proliferative enteropathy.

Infection of sparrows (Passer domesticus) and different mice strains with Lawsonia intracellularis

The susceptibility of sparrows (Passer domesticus) and strains of mice (Swiss, BALB/c, C-57 and DB-A) to Lawsonia intracellularis infection was studied. Thirty-two sparrows were inoculated with pure culture of L. intracellularis and eleven received sham inoculum. Feces were collected on -1, 7, 14 and 21 days post infection (dpi) for detection of L. intracellularis by PCR. After 21 days, all sparrows were euthanized and the tissues processed for histology and immunohistochemistry (IHC). One hundred sixty mice of four different strains (n=40, per strain) were used. For each mouse strain, 16 animals received mucosa homogenate from a pig infected with L. intracellularis, 16 received pure culture of L. intracellularis and eight animals received sham inoculum. Two control and four inoculated mice from each group were euthanized on 7, 14, 21 and 28 dpi. Sections of intestine were collected for histologic analysis and IHC and pooled feces were collected for L. intracellularis PCR. None of the sparrows had any histologic lesions characteristic of proliferative enteropathy or antigen labeling by IHC. All sparrow fecal samples were negative by PCR. All mice strains studied had histopathological lesions typical of PE and IHC labeling consistent with L. intracellularis infection, especially those animals inoculated with pure culture. The most severe lesions were observed in DB-A and Swiss mice. Fecal shedding was detected in all mice strains, with peak at 14 dpi. We conclude that sparrows do not seem to be relevant in the epidemiology of L. intracellularis. The results showed variations in the lesions among the four mice strains used.

Proliferative enteropathy (PE)-induced changes in the calbindin-immunoreactive (CB-IR) neurons of inferior mesenteric ganglion supplying the descending colon in the pig

A subpopulation of the pig inferior mesenteric ganglia (IMG) neurons projecting to the colon exhibit calbindin-like immunoreactivity. It is not known if there are any changes in the chemical coding patterns of these neurons during porcine proliferative enteropathy (PE). To answer this question, juvenile Large White Polish pigs with clinically diagnosed Lawsonia intracellularis infection (PE; n = 3) and a group of uninfected controls (C; n = 3) were compared. The retrograde tracer fast blue (FB) was injected into the descending colons of all animals and then tissue comprising IMGs from both groups was processed for double-labeling immunofluorescence with calbindin-D28k (CB) in combination with either tyrosine hydroxylase (TH), neuropeptide Y (NPY), somatostatin (SOM), vasoactive intestinal polypeptide (VIP), nitric oxide synthase, Leu-enkephalin, substance P, vesicular acetylcholine transporter, galanin, or pituitary adenylate cyclase-activating polypeptide. Immunohistochemistry revealed changes in the chemical coding pattern of calbindin-immunoreactive neurons in the inferior mesenteric ganglia of the pig. In control animals, FB/CB-positive neurons were immunoreactive to TH, NPY, SOM, and VIP. In the experimental group, TH-expressing neurons were unaffected, NPY-expressing neurons were increased, whereas the number of neurons immunoreactive to SOM or VIP was reduced. Changes in chemical coding of CB neurons during PE may play an important role in adaptation of these IMG cells under pathological conditions.

Citrobacter Infection and Wnt signaling

Gut flora generally contributes to a healthy environment while both commensal and pathogenic bacteria that influence the innate and adaptive immune responses, can cause acute and/or chronic mucosal inflammation. Citrobacter rodentium (C. rodentium) is a member of the family of enteropathogens that provide an excellent in vivo model to investigate the host-pathogen interactions in real-time. It is the etiologic agent for transmissible murine colonic hyperplasia (TMCH) while inflammation following C. rodentium infection is dependent upon the genetic background. Ongoing and completed studies in this model have so far established that Wnt/β-catenin, Notch and PI3K pathways regulate colonic crypt hyperplasia while epithelial-stromal cross-talk, mediated by MEK/ERK/NF-κB signaling, regulates inflammation and/or colitis in susceptible strains. The C. rodentium-induced hyperplastic state also increases the susceptibility to either mutagenic insult or in mice heterozygous for Apc gene. The ability to modulate the host response to C. rodentium infection therefore provides an opportunity to delineate the mechanisms that determine mucosal hyperplasia, intestinal inflammation, and/or neoplasia as disease outcomes.

Investigation of the association of growth rate in grower-finishing pigs with the quantification of Lawsonia intracellularis and porcine circovirus type 2

As a part of a prospective cohort study in four herds, a nested case control study was carried out. Five slow growing pigs (cases) and five fast growing pigs (controls) out of 60 pigs were selected for euthanasia and laboratory examination at the end of the study in each herd. A total of 238 pigs, all approximately 12 weeks old, were included in the study during the first week in the grower-finisher barn. In each herd, approximately 60 pigs from four pens were individually ear tagged. The pigs were weighed at the beginning of the study and at the end of the 6-8 weeks observation period. Clinical data, blood and faecal samples were serially collected from the 60 selected piglets every second week in the observation period. In the killed pigs serum was examined for antibodies against Lawsonia intracellularis (LI) and procine circovirus type 2 (PCV2) and in addition PCV2 viral DNA content was quantified. In faeces the quantity of LI cells/g faeces and number of PCV2 copies/g faeces was measured by qPCR. The objective of the study was to examine if growth rate in grower-finishing pig is associated with the detection of LI and PCV2 infection or clinical data. This study has shown that diarrhoea is a significant risk factor for low growth rate and that one log(10) unit increase in LI load increases the odds ratio for a pig to have a low growth rate by 2.0 times. Gross lesions in the small intestine and LI load>log(10)6/g were significant risk factors for low growth. No association between PCV2 virus and low growth was found.

Changes in pituitary adenylate cyclase-activating Peptide 27-like immunoreactive nervous structures in the porcine descending colon during selected pathological processes

This study reports on changes in the pituitary adenylate cyclase-activating peptide 27-like immunoreactive (PACAP-27-LI) nerve structures of the enteric nervous system (ENS) in the porcine descending colon, caused by chemically induced inflammation, nerve injury, and proliferative enteropathy (PE), which is a "natural" inflammation of the porcine digestive tract. The distribution pattern of PACAP-27-LI structures was studied using the immunofluorescence technique in the circular muscle layer, enteric plexuses (i.e., myenteric plexus (MP), outer submucous plexus (OSP), and inner submucous plexus (ISP)), and in the mucosal layer. Under physiological conditions, PACAP-27-LI perikarya have been shown to constitute 4.04 ± 0.66, 6.66 ± 0.77, and 11.19 ± 0.74 % in the MP, OSP, and ISP, respectively. Changes in PACAP-27 immunoreactivity depended on the pathological factor studied. The numbers of the PACAP-27-LI perikarya amounted to 12.26 ± 1.43, 12.28 ± 0.79, and 21.13 ± 1.19 % in chemically induced colitis, 17.83 ± 0.88, 9.03 ± 1.05, and 20.72 ± 1.35 % during PE and 10.65 ± 0.82, 6.88 ± 1.04, and 14.04 ± 1.09 % after axotomy in MP, OSP, and ISP, respectively. All of the studied processes generally resulted in an increase in the number of PACAP-27-LI nerve fibers in the circular muscle and mucosal layers. The obtained results suggest that PACAP-27-LI nerve structures of ENS may participate in various pathological states within the porcine descending colon, and their functions probably depend on the type of pathological factor.

A novel Lawsonia intracellularis autotransporter protein is a prominent antigen

Investigation of antigenic determinants of the microaerophilic obligate intracellular bacterium Lawsonia intracellularis using a mass spectrometry approach identified a novel bacterial protein present in an extract of cell culture medium aspirated from heavily infected in vitro cell cultures. Western immunoblotting analysis of SDS-PAGE-resolved proteins using immune sera pooled from L. intracellularis-infected pigs revealed the presence of a strongly immunoreactive band of ∼ 72 kDa. Liquid chromatography-electrospray ionization-tandem mass spectrometry analysis of this component and database mining using a fully annotated L. intracellularis genome sequence and the comprehensive GenBank prokaryotic genomic database highlighted the presence of a protein that shares little sequence similarity with other prokaryotic proteins and appears to be highly species specific. Detailed bioinformatic analyses identified the protein as member of the autotransporter protein family of surface-exposed proteins, and the designation LatA (Lawsonia autotransporter protein A) is suggested. Recognition of recombinant LatA on Western blots by a panel of sera from infected and control pigs corresponded 100% with a commercial serodiagnostic that relies on in vitro culture of this fastidious organism. LatA therefore represents a potential candidate for the development of a rapid and species-specific serodiagnostic reagent.

The association of Streptococcus bovis/gallolyticus with colorectal tumors: the nature and the underlying mechanisms of its etiological role

Streptococcus bovis (S. bovis) bacteria are associated with colorectal cancer and adenoma. S. bovis is currently named S. gallolyticus. 25 to 80% of patients with S. bovis/gallolyticus bacteremia have concomitant colorectal tumors. Colonic neoplasia may arise years after the presentation of bacteremia or infectious endocarditis of S. bovis/gallolyticus. The presence of S. bovis/gallolyticus bacteremia and/or endocarditis is also related to the presence of villous or tubular-villous adenomas in the large intestine. In addition, serological relationship of S. gallolyticus with colorectal tumors and direct colonization of S. gallolyticus in tissues of colorectal tumors were found. However, this association is still under controversy and has long been underestimated. Moreover, the etiological versus non-etiological nature of this associationis not settled yet. Therefore, by covering the most of up to date studies, this review attempts to clarify the nature and the core of S. bovis/gallolyicus association with colorectal tumors and analyze the possible underlying mechanisms.

The struggle within: microbial influences on colorectal cancer

Recently, an unprecedented effort has been directed at understanding the interplay between chronic inflammation and development of cancer, with the case of inflammatory bowel disease (IBD)-associated colorectal cancer at the forefront of this research endeavor. The last decade has been particularly fertile, with the discovery of numerous innovative paradigms linking various inflammatory, proliferative, and innate and adaptive immune signaling pathways to the development of colorectal cancer. Because of the preponderant role of the intestinal microbiota in the initiation and progression of IBD, recent efforts have been directed at understanding the relationship between bacteria and colorectal cancer. The microbiota and its collective genome, the microbiome, form a diverse and complex ecological community that profoundly impacts intestinal homeostasis and disease states. This review will discuss the differential influence of the microbiota on the development of IBD-associated colorectal cancer and highlight the role of innate immune sensor-dependent as well as -independent mechanisms in this pathology.

Effector prediction in host-pathogen interaction based on a Markov model of a ubiquitous EPIYA motif

Background

Effector secretion is a common strategy of pathogen in mediating host-pathogen interaction. Eight EPIYA-motif containing effectors have recently been discovered in six pathogens. Once these effectors enter host cells through type III/IV secretion systems (T3SS/T4SS), tyrosine in the EPIYA motif is phosphorylated, which triggers effectors binding other proteins to manipulate host-cell functions. The objectives of this study are to evaluate the distribution pattern of EPIYA motif in broad biological species, to predict potential effectors with EPIYA motif, and to suggest roles and biological functions of potential effectors in host-pathogen interactions.

Results

A hidden Markov model (HMM) of five amino acids was built for the EPIYA-motif based on the eight known effectors. Using this HMM to search the non-redundant protein database containing 9,216,047 sequences, we obtained 107,231 sequences with at least one EPIYA motif occurrence and 3115 sequences with multiple repeats of the EPIYA motif. Although the EPIYA motif exists among broad species, it is significantly over-represented in some particular groups of species. For those proteins containing at least four copies of EPIYA motif, most of them are from intracellular bacteria, extracellular bacteria with T3SS or T4SS or intracellular protozoan parasites. By combining the EPIYA motif and the adjacent SH2 binding motifs (KK, R4, Tarp and Tir), we built HMMs of nine amino acids and predicted many potential effectors in bacteria and protista by the HMMs. Some potential effectors for pathogens (such as Lawsonia intracellularis, Plasmodium falciparum and Leishmania major) are suggested.

Conclusions

Our study indicates that the EPIYA motif may be a ubiquitous functional site for effectors that play an important pathogenicity role in mediating host-pathogen interactions. We suggest that some intracellular protozoan parasites could secrete EPIYA-motif containing effectors through secretion systems similar to the T3SS/T4SS in bacteria. Our predicted effectors provide useful hypotheses for further studies.

Application of a pig ligated intestinal loop model for early Lawsonia intracellularis infection

Background

Porcine proliferative enteropathy in pigs is caused by the obligate, intracellular bacterium Lawsonia intracellularis. In vitro studies have shown close bacterium-cell interaction followed by cellular uptake of the bacterium within 3 h post inoculation (PI). However, knowledge of the initial in vivo interaction between porcine intestinal epithelium and the bacterium is limited. The aims of the present study were to evaluate the usefulness of a ligated small intestinal loop model to study L. intracellularis infections and to obtain information on the very early L. intracellularis-enterocyte interactions.

Methods

A ligated small intestinal loop model using three different L. intracellularis inocula was applied to 10-11-week-old pigs. The inocula were 1) wild type bacteria derived from overnight incubation of L. intracellularis bacteria from spontaneous disease, 2) crude vaccine bacteria (Enterisol^® Ileitis Vet), and 3) vaccine bacteria propagated in cell culture. The bacteria-enterocyte interaction was visualised using immunohistochemistry on specimens derived 1, 3 and 6 h PI respectively.

Results

Although at a low level, close contact between bacteria and the enterocyte brush border including intracellular uptake of bacteria in mature enterocytes was seen at 3 and 6 h PI for the vaccine and the propagated vaccine inocula. Interaction between the wild-type bacteria and villus enterocytes was scarce and only seen at 6 h PI, where a few bacteria were found in close contact with the brush border.

Conclusions

The ligated intestinal loop model was useful with respect to maintaining an intact intestinal morphology for up to 6 h. Furthermore, the study demonstrated that L. intracellularis interacts with villus enterocytes within 3 to 6 h after inoculation into intestinal loops and that the bacterium, as shown for the vaccine bacteria, propagated as well as non-propagated, was able to invade mature enterocytes. Thus, the study demonstrates the early intestinal invasion of L. intracellularis in vivo.

Early pathogenesis in porcine proliferative enteropathy caused by Lawsonia intracellularis

The intestinal bacterium Lawsonia intracellularis, the cause of proliferative enteropathy (PE) in pigs, is believed to infect mitotically active epithelial cells of the intestinal crypts and then multiply and spread in these cells as they divide. Further spread of infection is thought to occur by shedding of bacteria from infected crypts followed by infection of new crypts. The early stages of the pathogenesis of PE, from 0 to 48 hours post-infection (hpi), have not been studied in vivo. In the present study pigs were inoculated with L. intracellularis and killed from 12 hpi to 5 days post-infection (dpi). The localization of L. intracellularis was determined immunohistochemically and by fluorescence in-situ hybridization. At 12 hpi L. intracellularis was found within epithelial cells at the tips of villi, indicating infection of a range of epithelial cells including mature differentiated enterocytes. Furthermore, early invasion of the intestinal connective tissue was observed; with the presence of single bacteria in the lamina propria 12 hpi, and with a further spread of bacteria in the lamina propria observed at 5 dpi, suggesting an active role for the lamina propria in the course of infection.

Changes in the somatostatin (SOM)-like immunoreactivity within nervous structures of the porcine descending colon under various pathological factors

This study reports on changes in the somatostatin-like immunoreactive (SOM-LI) nerve structures of the enteric nervous system (ENS) in the porcine descending colon, caused by chemically driven inflammation, proliferative enteropathy (PE), which is a "natural" inflammation with proliferative changes and nerve injury (axotomy). The distribution pattern of SOM-LI structures was studied using the immunofluorescence technique in the circular muscle layer, the myenteric (MP), outer submucous (OSP) and inner submucous plexuses (ISP) and also in the mucosal layer. Under physiological conditions SOM-LI perikarya have been shown to constitute 1.97+/-0.36%, 2.06+/-0.33% and 4.23+/-0.40% in the MP, OSP and ISP, respectively. Changes in SOM-immunoreactivity depended on the pathological factor and the part of the ENS studied. Numbers of the SOM-LI perikarya amounted 1.81+/-0.30, 1.97+/-0.24 and 11.15+/-0.95 during chemically induced colitis and 3.21+/-0.37%, 4.33+/-0.33% and 4.42+/-0.32% after axotomy in MP, OSP and ISP, respectively. Moreover during PE SOM-positive cell bodies were not observed at all in MP, whereas within OSP and ISP the number of SOM-LI perikarya amounted to 3.34+/-0.36 and 10.92+/-059, respectively. All processes studied resulted in a decrease in the number of SOM-LI nerve fibers in the mucosal layer, whereas within the circular muscle layer chemically induced inflammation and axotomy caused an increase in the number of the SOM-LI nerve fibers contrary to PE, which reduced the number of such fibers. The obtained results suggest that SOM-LI nerve structures of the ENS may participate in various pathological states within the porcine descending colon and their functions probably depend on the type of pathological factor.