Isolation of an intracellular bacterium from hamsters (Mesocricetus auratus) with proliferative ileitis and reproduction of the disease with a pure culture

PREVALENCE OF LAWSONIA INTRACELLULARIS INFECTION IN NONHUMAN PRIMATES AND PEST RODENTS IN A ZOOLOGICAL COLLECTION

In 2016 and 2017, Lawsonia intracellularis was isolated from several pileated gibbons (Hylobates pileatus) presenting with diarrhea in Mulhouse Zoo (eastern France). To this day, infection with this bacterium has rarely been described in nonhuman primates (NHP) in captivity or in the wild and there are no data about the prevalence or transmission of the disease. This study focuses on finding the prevalence of this infection amongst Mulhouse Zoo's NHP collection and trying to identify a source of contamination responsible for this epizooty. Forty-eight real-time PCR were conducted on feces from all NHP species in the zoo and on small mammals trapped in the NHP housing structures. No NHP was experiencing symptoms at the time of the study, however test results showed that Lawsonia intracellularis can be found in 61.76% (21/34) of the group total (n = 34) and the prevalence even increases to 92.3% (12/13) in the Lemuriform infraorder (n = 13). In small mammals (n = 14), prevalence of the bacterium is 57.17% (8/14) including 77.78% in rodents (7/9). The results of this study show that several NHP species are healthy carriers and some species of small mammals can be considered as a potential source of contamination. Because of the difficulty encountered trying to isolate the bacterium, it is plausible that infections caused by Lawsonia intracellularis have been underdiagnosed to this day, and that it could be an emerging disease in Europe. Therefore, using real-time PCR to search for this bacterium seems essential in case of diarrhea occurring in nonhuman primates. Moreover, even though further studies on contamination sources need to be conducted, the issue of the presence of rodents in NHP housing structures has to be taken very seriously and tackled with the utmost care.

Evaluation of immunogenicity and protection mediated by Lawsonia intracellularis subunit vaccines

Lawsonia intracellularis is an economically important bacterium that causes ileitis in pigs. Current vaccines for L. intracellularis do not allow for differentiation between infected and vaccinated animals (DIVA), which is beneficial for disease tracking and surveillance. Previously, we identified five putative surface L. intracellularis proteins that were targeted by antibodies from pigs infected with L. intracellularis which could serve as antigens in a subunit vaccine. We conducted two trials to determine whether these antigens were immunogenic and provided protection against infectious challenge and whether truncated glycoprotein D could be used as a DIVA antigen. For Trial 1, 5 week-old piglets were administered intramuscular monovalent vaccines comprised of a recombinant (r) flagella subunit protein (rFliC,) and DIVA antigen (truncated glycoprotein D (TgD), a herpes virus antigen) both formulated with a combination adjuvant consisting of polyinosinic:polycytidylic acid(poly I:C), host defense peptide 1002 and polyphosphazene, referred to as Triple Adjuvant (TriAdj). Relative to control animals, animals vaccinated with rFliC and rTgD had significantly elevated antigen-specific humoral immunity in sera suggesting that rFliC and TgD are immunogenic. Control animals had negligible anti-TgD titres suggesting that TgD may be a suitable DIVA antigen for pigs. For Trial 2, piglets were immunized with a trivalent vaccine (FOG vaccine consisting of rFLiC, rOppA protein (a ABC Type dipeptide transport system) and rGroEL (a stress response protein)) and a divalent vaccine (CM vaccine consisting of rClpP (an ATP-dependent Clp protease proteolytic subunit) and rMetK (a S-adenosyl methionine synthase)) formulated with Emulsigen®. Relative to the control pigs, pigs immunized with the FOG vaccine produced robust and significantly higher serum IgG antibodies against rFliC and rGroEL, and significantly higher anti-FliC and anti-GroEL IgA antibodies in jejunal (GroEL only) and ileal intestinal mucosa. Pigs immunized with CM vaccine produced significantly higher serum antibodies against rClpP and rMetK and significantly higher anti-rClpP IgA antibodies in the ileum relative to the control pigs. Quantitative polymerase chain reaction (qPCR) analysis showed that 18 days after challenge with infectious L. intracellularis, challenged/control pigs and pigs that received the CM vaccine, but not the pigs vaccinated with the FOG vaccine, shed significantly more bacteria in feces than the unchallenged controls pigs. These data suggest that the FOG vaccinated pigs showed limited protection. While promising, more work is needed to enhance the efficiency of the intramuscular vaccine to show significant disease protection.

Lawsonia intracellularis: Revisiting the Disease Ecology and Control of This Fastidious Pathogen in Pigs

Lawsonia intracellularis is an anaerobic obligate intracellular bacterium infecting the small intestine and infrequently also the large intestine of pigs and other animals including hamsters and horses. The infection is characterized by proliferation, hemorrhage, necrosis, or any combination commonly referred to as "ileitis," affecting the health and production efficacy of farmed pigs. Despite decades of research on this pathogen, the pathogenesis and virulence factors of this organism are not clearly known. In pigs, prophylaxis against L. intracellularis infection is achieved by either administration of subtherapeutic levels of in-feed antibiotic growth promoters or vaccination. While the former approach is considered to be effective in L. intracellularis control, potential regulations on subtherapeutic antibiotics in many countries in the near future may necessitate alternative approaches. The potential of manipulating the gut microbiome of pigs with feed ingredients or supplements to control L. intracellularis disease burden is promising based on the current understanding of the porcine gut microbiome in general, as well as preliminary insights into the disease ecology of L. intracellularis infection accrued over the last 30 years.

Biology and Diseases of Hamsters

The hamster species used as research models include the Syrian (golden), Mesocricetus auratus; the Chinese (striped-back), Cricetulus griseus; the Armenian (gray), C. migratorius; the European, Cricetus cricetus; and the Djungarian, Phodopus campbelli (Russian dwarf) and P. sungorus (Siberian dwarf). Hamsters are classified as members of the order Rodentia, suborder Myomorpha, superfamily Muroidea and in family Cricetidae. Animals in this family are characterized by large cheek pouches, thick bodies, short tails, and an excess of loose skin. They have incisors that erupt continuously and cuspidate molars that do not continue to grow ((I 1/1, C 0/0, PM 0/0, M 3/3) × 2 = 16). In 2010, it was reported that approximately 146,000 hamsters were used in research in the United States (United States Department of Agriculture, 2010).

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.

Species-specificity of equine and porcine Lawsonia intracellularis isolates in laboratory animals

Lawsonia intracellularis infection causes proliferative enteropathy (PE) in many mammalian species, with porcine and equine proliferative enteropathy (PPE and EPE) known worldwide. Hamsters are a well-published animal model for PPE infection studies in pigs. There is no laboratory animal model for EPE infection studies and it is not known whether there is species-specificity for equine or porcine isolates of L. intracellularis in animal models. The objective of this study was to determine whether it is possible to generate typical EPE lesions in hamsters after inoculation with an equine strain of L. intracellularis (EPE strain) and whether it is comparatively possible to generate PPE lesions in rabbits after inoculation with a porcine strain of L. intracellularis (PPE strain). In 2 separate trials, 4-week-old and 3-week-old weanling golden Syrian hamsters were challenged with EPE strains and compared to uninfected (both trials) and PPE-infected controls (Trial 2 only). Concurrently, 6 female New Zealand white juvenile rabbits were infected with PPE strain and observed concomitantly to 8 similar rabbits infected with EPE strain for a different experiment. Hamsters and rabbits were observed for 21 to 24 days post-infection (DPI), depending on the experiment. Neither infected species developed clinical signs. The presence of disease was assessed with diagnostic techniques classically used for pigs and horses: immune-peroxidase monolayer assay on sera; quantitative polymerase chain reaction (qPCR) detection of molecular DNA in feces; and hematoxylin and eosin (H&E) stain and immunohistochemistry (IHC) on intestinal tissues. Our results showed that EPE-challenged hamsters do not develop infection when compared with PPE controls (IHC, P = 0.009; qPCR, P = 0.0003). Conversely, PPE-challenged rabbits do not develop typical intestinal lesions in comparison to EPE-challenged rabbits, with serological response at 14 DPI being significantly lower (P = 0.0023). In conclusion, PPE and EPE strains appear to have different host-specificities for hamsters and rabbits, respectively.

Comparative genome sequencing identifies a prophage-associated genomic island linked to host adaptation of Lawsonia intracellularis infections

Lawsonia intracellularis is an obligate intracellular bacterium and the causative agent of proliferative enteropathy (PE). The disease is endemic in pigs, emerging in horses and has also been reported in a variety of other animal species, including nonhuman primates. Comparing the whole genome sequences of a homologous porcine L. intracellularis isolate cultivated for 10 and 60 passages in vitro, we identified a 18-kb prophage-associated genomic island in the passage 10 (pathogenic variant) that was lost in the passage 60 (non-pathogenic variant). This chromosomal island comprises 15 genes downstream from the prophage DLP12 integrase gene. The prevalence of this genetic element was evaluated in 12 other L. intracellularis isolates and in 53 infected animals and was found to be conserved in all porcine isolates cultivated for up to 20 passages and was lost in isolates cultivated for more than 40 passages. Furthermore, the prophage region was also present in 26 fecal samples derived from pigs clinically affected with both acute and chronic forms of the disease. Nevertheless, equine L. intracellularis isolates evaluated did not harbor this genomic island regardless of the passage in vitro. Additionally, fecal samples from 21 clinically affected horses and four wild rabbits trapped in horse farms experiencing PE outbreaks did not show this prophage-associated island. Although the presence of this prophage-associated island was not essential for a virulent L. intracellularis phenotype, this genetic element was porcine isolate-specific and potentially contributed to the ecological specialization of this organism for the swine host.

The rabbit as an infection model for equine proliferative enteropathy

The objective of this study was to demonstrate the susceptibility of rabbits to Lawsonia intracellularis obtained from a case of clinical equine proliferative enteropathy (EPE). This is a preliminary step toward developing a rabbit infection model for studying pathogenesis and therapy of EPE in horses. Nine does were equally assigned to 3 groups. Animals in 2 groups (Group 1 and Group 2) were orally inoculated with different doses of cell-cultured L. intracellularis. Controls (Group 3) were sham-inoculated. Feces and blood were collected before the rabbits were infected and at 7, 14, and 21 days post-infection (DPI). Serum immunoglobulin G (IgG) titers were measured using an immunoperoxidase monolayer assay (IPMA) and fecal samples were analyzed with quantitative polymerase chain reaction (qPCR). A doe from each group was euthanized at 7, 14, and 21 DPI for collection and evaluation of intestinal samples. Tissues were stained by routine hematoxylin and eosin (H&E) method and immunohistochemistry (IHC) with L. intracellularis-specific mouse monoclonal antibody. At 14 DPI, serologic responses were detected in both infected groups, which maintained high titers through to 21 DPI. Lawsonia intracellularis DNA was detected in the feces of Group 2 on 7 DPI and in both infected groups on 14 DPI. Gross lesions were apparent in Group 1 and Group 2 on 14 DPI. Immunohistochemistry confirmed L. intracellularis antigen within cells of rabbits in Group 1 and Group 2 on 7, 14, and 21 DPI. No lesions, serologic response, shedding, or IHC labeling were found in Group 3 rabbits. This study describes an EPE rabbit model that simulates natural infection, as typical lesions, immune response, and fecal shedding were present.

Genome Sequence of Lawsonia intracellularis Strain N343, Isolated from a Sow with Hemorrhagic Proliferative Enteropathy

Lawsonia intracellularis is the etiological agent of proliferative enteropathy (PE), causing mild or acute hemorrhagic diarrhea in infected animals. Here we report the genome sequence of strain N343, isolated from a sow that died of hemorrhagic PE. N343 contains 24 single nucleotide polymorphisms and 90 indels compared to the reference strain PHE/MN1-00.

Proliferative enteropathy involving Lawsonia intracellularis infection in rabbits (Oryctlagus cuniculus)

Five rabbits suffering from diarrhea were diagnosed with proliferative enteropathy (PE). Histopathology revealed a thickened mucosa consisting of hyperplastic intestinal epithelium and infiltration of inflammatory cells mainly consisted of macrophages. In the affected epithelial cytoplasm, numerous curved bacillus-like organisms were observed in the Warthin-Starry silver stain and electron microscopy observation. In polymerase chain reactions, Lawsonia intracellularis-specific DNA fragment were amplified from affected ileal tissue extracted DNA in each case and present 5 cases were confirmed to be L. intracellularis infection. Serum collected from the affected rabbit was immunohistochemically reactive with L. intracellularis in tissue sections from pigs with porcine proliferative enteropathy, as well as with tissue sections from the five affected rabbits. Thus, serum obtained from the affected rabbit may be applicable to immunohistochemical detection for L. intracellularis infection in other species.

Proliferative enteropathy: a global enteric disease of pigs caused byLawsonia intracellularis

Proliferative enteropathy (PE; ileitis) is a common intestinal disease affecting susceptible pigs raised under various management systems around the world. Major developments in the understanding of PE and its causative agent,Lawsonia intracellularis, have occurred that have led to advances in the detection of this disease and methods to control and prevent it. Diagnostic tools that have improved overall detection and early onset of PE in pigs include various serological and molecular-based assays. Histological tests such as immunohistochemistry continue to be the gold standard in confirmingLawsonia-specific lesions in pigspost mortem. Despite extreme difficulties in isolatingL. intracellularis, innovations in the cultivation and the development of pure culture challenge models, have opened doors to better characterization of the pathogenesis of PE throughin vivoandin vitro L. intracellularis–host interactions. Advancements in molecular research such as the genetic sequencing of the entireLawsoniagenome have provided ways to identify various immunogens, metabolic pathways and methods for understanding the epidemiology of this organism. The determinations of immunological responsiveness in pigs to virulent and attenuated isolates ofL. intracellularisand identification of various immunogens have led to progress in vaccine development.

Routine diagnostics of Lawsonia intracellularis performed by PCR, serological and post mortem examination, with special emphasis on sample preparation methods for PCR

The aim of this study was to find suitable and reliable tools for demonstrating Lawsonia intracellularis in routine clinical diagnosis. Firstly, a method to prepare tissue samples before a polymerase chain reaction (PCR) was evaluated in pigs submitted for necropsy. Secondly, seven different faecal preparation methods and four different DNA polymerases were tested in single or nested PCR, with co-amplification of a mimic molecule. Thirdly, in selected pigs submitted for necropsy, tissue and faecal samples were examined histopathologically and by PCR, and blood samples were analysed serologically. Detection of L. intracellularis in tissue preparations by PCR showed good specificity and correlated to lesions found at necropsy. The sensitivity in spiked tissue samples was 10(1)-10(2) mimic molecules per tube. In faecal samples, nested PCR on boiled lysate gave the best result with a sensitivity of 10(2)-10(3) mimic molecules per reaction tube. However, because of the time-consuming procedure and the increased risk for contamination, a commercially available kit was preferred for routine diagnoses, despite a somewhat lower detection rate in subclinically infected pigs. In a few cases, the serological results differed from those obtained by PCR and by necropsy but the reason for this is not clear. This study indicates that the best method for diagnosis of acute enteritis in growers is PCR on faecal or tissue samples. To determine the presence of the bacteria in a herd, serology or repeated faecal sampling for PCR from target animals, or both, should be used.

Diagnosis of porcine proliferative enteropathy: detection of Lawsonia intracellularis by pathological examinations, polymerase chain reaction and cell culture inoculation

A total of 21 pigs aged 7-17 weeks with clinical symptoms suggestive for Porcine Proliferative Enteropathy were examined for Lawsonia intracellularis by analysing the following parameters: (i) intestinal gross and histological lesions, (ii) presence of comma-shaped bacteria in enterocytes by Warthin-Starry and a modified Ziehl-Neelsen stain, (iii) PCR amplification of L. intracellularis DNA from intestinal mucosa by using two oligonucleotide primer pairs targeting a 255-bp DNA fragment of the 16S rDNA-gene and a 319-bp DNA fragment of the L. intracellularis chromosome. Specificity of PCR reactions was confirmed by using DNA extracted from the L. intracellularis reference strain N343 (ATCC 55672) as well as by DNA sequence comparisons of PCR amplification products with data bank entries. Intestinal gross lesion indicative for PPE were observed in 20 pigs (95.2%). For all 21 pigs, the L. intracellularis aetiology was confirmed by histological as well as bacterioscopical examinations. Specific PCR amplification products were obtained from 20 pigs (95.2%). Taking PCR positivity as the definite criterion, L. intracellularis was diagnosed in 20 pigs from 11 herds in seven Swiss cantons (Argovia, Berne, Fribourg, Grisons, Lucerne, Schwyz, Thurgovia). To grow L. intracellularisin vitro, the cell culture method of Lawson et al. (J. Clin. Microbiol. 1993: 31, 1136-1142) was adopted. Inocula prepared from heavily infected fresh and frozen ileal mucosa of 15 pigs were cultured in rat enterocytic IEC-18 cells (ATCC CRL 1589). Six cell culture passages of 10 days each were completed. The reference strain N343 was examined for cultivability, accordingly. Except for occasional specific PCR amplifications from cell cultures up to the second passage, any indications for growth of L. intracellularis in IEC-18 cells were not found.

Spontaneous terminal ileitis resembling Crohn disease in captive tamarins

Five tamarins (four Saguinus mystax and one S. labiatus) died with wasting syndrome characterized by chronic diarrhea at the Center for Reproduction and Conservation of Non-Human Primates in Iquitos, Peru. At necropsy, the terminal ileum of all affected tamarins was found to be markedly thickened. Histologically, the terminal ileal mucosa was completely ulcerated, and effaced by debris and mononuclear inflammatory cells. The submucosa and serosa were thickened by fibroplasia, mononuclear cell infiltrates and variable edema. No infectious agent was observed. The lesions were similar to those described previously for Crohn disease. This is to our knowledge the first report of terminal ileitis resembling Crohn disease in non-human primates.

Lawsonia intracellularis: getting inside the pathogenesis of proliferative enteropathy

Although proliferative enteropathy (PE) has been recognised for several decades, Lawsonia intracellularis, the aetiological agent, was identified formally in only 1995. This organism is both highly fastidious and obligately intracellular bacterium, characteristics which have inevitably restricted investigations in all aspects of its biology. Despite these limitations, advances have been made in characterising and understanding L. intracellularis-host interaction both in vivo and in vitro. Based upon evidence provided by mainly pathological and histological investigations conducted to date, we review salient features of our current understanding of processes involved throughout the course of infection by this unique pathogen.

A member of the delta subgroup of proteobacteria from a pyogenic liver abscess is a typical sulfate reducer of the genus Desulfovibrio

Strain FH26001/95 (ATCC 700045) was previously isolated from a pyogenic liver abscess from a human. Comparative 16S rRNA gene sequence analysis showed that this strain is related to members of the delta subgroup of the proteobacteria, within a cluster of sulfate-reducing bacteria (Desulfovibrio spp.) and non-sulfate-reducing bacteria (Bilophila wadsworthia and Lawsonia spp.). The phenotype of strain FH26001/95 was found to be typical of members of the genus Desulfovibrio. Growth and substrate transformations were possible at oxygen concentrations of 2 to 5% (vol/vol) but not at oxygen concentrations of 21% (vol/vol) in air. Its isolation from an infection in a human suggests that some members of the genus Desulfovibrio can be considered opportunistic pathogens.

Gamma interferon influences intestinal epithelial hyperplasia caused by Lawsonia intracellularis infection in mice

Lawsonia intracellularis is a recently identified bacterial pathogen which causes disease in a broad range of animals. Invasion of intestinal epithelial cells and the resultant hyperplasia of infected cells are central processes in disease pathogenesis. In this study, we aimed to establish whether immunocompetent mice were susceptible to infection and whether gamma interferon (IFN-gamma) contributed to the pathogenesis of infection. Wild-type 129-Sv-Ev mice (129 mice) and IFN-gamma receptor knockout mice based on the 129 background (IFN-gammaR(-)) were challenged orally with approximately 5.5 x 10(7) L. intracellularis cells. Both 129 and IFN-gammaR(-) mice became infected, although the extent of infection (as determined by the proportion of infected crypts) was substantially lower in 129 mice than in IFN-gammaR(-) mice. Despite these differences, infected crypts showed characteristics typical of proliferative enteropathies of other animals, i.e., intracellular colonization of epithelial cells by L. intracellularis with resultant epithelial hyperplasia. Infection in 129 mice was cleared between days 21 and 28 postchallenge, whereas infection in IFN-gammaR(-) mice was evident in 100% of animals from day 21 onward. Additionally, in IFN-gammaR(-) mice the infection was so extensive that fatalities resulted. IFN-gamma therefore plays a significant role in limiting intracellular infection and increased cellular proliferation associated with L. intracellularis. L. intracellularis infection is generally associated with modest cellular infiltration; therefore, further comparative examinations will be necessary to determine pathogenicity factors and define the role of IFN-gamma in controlling this infection.

Diagnosis of proliferative enteritis in frozen and formalin-fixed, paraffin-embedded tissues from a hamster, horse, deer and ostrich using a Lawsonia intracellularis-specific multiplex PCR assay

Proliferative enteritis (PE) is an enteric disease that has been reported in a variety of animals. It is caused by an obligate intracellular bacterium identified in swine as Lawsonia intracellularis. The organism can be detected ante-mortem in swine with PE using molecular diagnostic methods. The disease can be diagnosed post-mortem in all species by gross examination of tissues and special histologic staining procedures. In this study we extracted total DNA from frozen or formalin-fixed, paraffin-embedded tissues from cases of pig, hamster, horse, deer and ostrich PE. The samples were subjected to a multiplex PCR reaction using primers specific for a swine isolate of L. intracellularis. Identical sized PCR products were detected in samples from all animals with PE and the specificity of the PCR reaction for L. intracellularis was demonstrated by Southern-blotting and hybridization using specific probes. These results suggest that the intracellular organism of PE in these species are all very closely related to the causative agent of PE in swine, L. intracellularis. In addition, this multiplex PCR assay can be used to detect the organism in frozen or archival tissues, facilitating retrospective diagnosis of PE.

Developed and resolving lesions in porcine proliferative enteropathy: possible pathogenetic mechanisms

Proliferative enteropathy, caused by Lawsonia intracellularis, offers the opportunity to examine bacterial mechanisms that influence epithelial cell proliferation. Ultrastructural features of developed and resolving lesions included the presence of enlarged intestinal crypts containing undifferentiated immature epithelial cells and an absence of goblet cells. Numerous intracytoplasmic bacteria, identified as L. intracellularis, were consistently present within affected cells. In recovering intestinal tissue, additional features were (1) the common presence of pale, swollen, protruding epithelial cells, (2) shrunken, degenerate epithelial cells, (3) apoptotic bodies in both epithelial cells and macrophages, (4) the reappearance of normal goblet cells, and (5) reduced numbers of L. intracellularis within lesions. Bacteria were released from cells via cytoplasmic and cellular protrusions into the intestinal lumen. It is speculated that the presence of the intracytoplasmic bacterium, L. intracellularis, may disrupt normal processes of cell growth, differentiation or apoptosis in the intestinal epithelium.

Entry of the bacterium ileal symbiont intracellularis into cultured enterocytes and its subsequent release

Separate suspensions of two strains of ileal symbiont (IS) intracellularis, an obligate intracellular bacterium and the causative agent of porcine proliferative enteropathy, were added to 40 or 80 per cent confluent monolayers of established cultures of rat (IEC-18) or pig enterocytes (IPEC-J2). Peak numbers of intracellular organisms were detected within the enterocytes six days later, but no cytopathic effects were evident. After an initial close association with the cell membrane of the enterocytes, single bacteria were internalised after three hours within membranes-bound vacuoles. The formation of an electron-dense projection between cell membranes and external bacteria was only evident if the bacterial suspensions were centrifuged on to the monolayers. The release of internalised bacteria into the cytoplasm, with the breakdown and loss of membrane-bound vacuoles, was also evident three hours after infection. Internalised bacteria were associated with, but not observed within, coated membrane pits. Mitochondria were closely associated with internalised vacuoles and with released bacteria. Two to six days after infection, multiplication of the bacteria free in the cytoplasm was frequently observed. In infected cells six days after the inoculation of monolayers, groups of bacteria were found within large, balloon-like, cytoplasmic protrusions, and the subsequent release of bacteria from the monolayer provided a means of bacterial exit from the cells. Many events in the in vitro culture model closely resembled events observed at the cellular level in animals infected with IS intracellularis and the model provides a useful basis for investigating the pathogenetic mechanisms of this bacterium.

Reproduction of proliferative enteritis in hamsters with a pure culture of porcine ileal symbiont intracellularis

Hamsters, three weeks old, were inoculated orally with suspensions of intracellular bacteria, grown in tissue culture cells, IEC-18, rat enterocytes. Cells had been infected with suspensions of intracellular bacteria derived from the lesions of proliferative haemorrhagic enteropathy occurring naturally in two pigs 916/91 and 1482/89. Infected cell lines containing each separate strain, 916/91 and 1482/89, were passaged one, two or five times and pure cultures of intracellular bacteria, identified as ileal symbiont intracellularis by immunological means, were collected from the cells and used as inocula. Ten of sixteen hamsters dosed with 916/91 passaged one or five times, developed lesions of proliferative enteritis evident as necropsy three weeks after inoculation. Hamsters inoculated with 1482/89 passaged twice and stored frozen, or IEC-18 cells alone or those left uninoculated, failed to develop lesions of proliferative enteritis. Campylobacter jejuni infection occurred throughout, in all groups. Marked hyperplasia of ileal enterocytes, associated with numerous intracellular curved bacteria was invariably detected in experimentally affected hamsters. Immunofluorescence reactions with specific antibodies indicated that these intracellular bacteria were also ileal symbiont intracellularis. The results suggested that proliferative enteritis could be reproduced in hamsters with a pure culture of an agent derived from pigs. We concluded that the reproduction of the disease with our inocula containing a single agent clarifies the aetiology of proliferative enteritis in both hamsters and pigs.

Intracellular Campylobacter-like organism from ferrets and hamsters with proliferative bowel disease is a Desulfovibrio sp

Proliferative bowel disease is an intestinal disorder of a variety of domestic animals associated with the presence of an intracellular Campylobacter-like organism (ICLO). We have identified the ICLO obtained from a ferret with proliferative colitis by 16S rRNA sequence analysis. In this ferret, proliferative bowel tissue containing the ICLO had translocated to the mesenteric lymph nodes, omentum, and liver. The 16S rRNA genes of the ICLO were amplified from an infected fragment of extraintestinal tissue by using universal prokaryotic primers. Approximately 1,480 bases of the amplified 16S rRNA gene were sequenced by cycle sequencing. Comparison of the sequence of the ICLO with those of over 400 bacteria in our data base indicated that the sequence of the ICLO was most closely related to that of Desulfovibrio desulfuricans (87.5% similarity). Phylogenetic analysis with 12 Desulfovibrio species and 20 species from related genera placed the ICLO in a subcluster within the genus Desulfovibrio with D. desulfuricans and 5 other Desulfovibrio species. We will refer to this organism as the intracellular Desulfovibrio organism (IDO). Specific primers were produced for PCR amplification of a 550-base fragment of the 16S rRNA gene of the IDO in proliferative intestinal tissue samples. This unique 550-base segment was amplified from samples of frozen intestinal tissue from nine ferrets and three hamsters with ICLO-associated disease but not in four intestinal tissue samples from animals without the ICLO-associated disease. The 550-base amplified products from the bowel tissues of one hamster and one ferret were fully sequenced. The ferret IDO partial sequence was identical to the previously determined 16S rRNA sequence over its length, and the hamster IDO sequence differed by a single base. The same intracellular organism has been identified in proliferative intestinal tissues of swine and that the organism has been successfully maintained in tissue culture. The availability of specific primers for PCR-based detection of this intracellular Desulfovibrio organism will aid in the determination of its role in the pathogenesis of proliferative bowel disease in a variety of infected hosts.

Experimentally induced proliferative enteritis in hamsters: an ultrastructural study

Hamsters, three weeks old, were dosed orally with suspensions of intracellular bacteria grown in rat enterocyte tissue culture cells IEC-18, which had been infected with suspensions of intracellular bacteria derived from the lesions of proliferative haemorrhagic enteropathy occurring naturally in two pigs. Each bacterial strain, identified as Ileal symbiont intracellularis, was passaged in the cell lines once, twice or five times, collected with the cells and used as inocula. Ten of 16 hamsters dosed with 916/91 passaged one or five times developed lesions of proliferative enteritis. In these 10 hamsters, marked hyperplasia of ileal enterocytes associated with numerous intracellular curved bacteria was detected. An ultrastructural study of epithelial cells in the ileum of affected hamsters showed numerous intracellular bacteria in the cytoplasm. Similar bacteria were not seen in unaffected animals. Intracellular bacteria were usually seen in groups and could appear as electron dense or in a more electron lucent form. These bacteria were clearly seen to enter cells from the intestinal lumen, via endocytic vacuoles at the brush border. There was rapid breakdown of the entry vacuoles, leaving bacteria free in the cytoplasm where division was usually observed. These bacteria were often seen in close association with normal or distended mitochondria and rough endoplasmic reticulum.

Relationship between Ileal symbiont intracellularis and porcine proliferative enteritis

The relationship between Ileal symbiont (IS) intracellularis, formerly known as a Campylobacter-like organism, and porcine proliferative enteritis (PE) was studied by use of pigs with experimentally transmitted PE. Twenty one pigs were experimentally inoculated with homogenized ileal mucosa from a pig that died with PE, and 7 were maintained as uninoculated controls. Fecal samples were collected, and pigs were necropsied weekly postinoculation. Light microscopy and electron microscopy were used to examine tissues for lesions of PE and infectious agents. DNA was extracted from the fecal samples and assayed for the presence of sequences specific for IS intracellularis by dot blot hybridization and polymerase chain reaction amplification. IS intracellularis was detected by the polymerase chain reaction in the feces of 20 of 21 inoculated pigs but not in the feces of uninoculated pigs. Seven inoculated pigs but no uninoculated pigs were detected shedding IS intracellularis by dot blot hybridization. Shedding was detected 1 to 5 weeks after inoculation, and clinical signs were seen in the second to fifth weeks after inoculation. Few pigs without lesions of PE were found to shed IS intracellularis. There was a highly significant association between the presence of IS intracellularis in feces or tissue and the presence of microscopic proliferative lesions and between the severity of the lesions of PE and the percentage of IS intracellularis-infected intestinal crypts. Pigs that ceased shedding IS intracellularis were significantly less likely to have proliferative lesions. These and previous reports are consistent with the hypothesis that IS intracellularis is a necessary causative agent of PE.

Reproduction of porcine proliferative enteropathy with pure cultures of ileal symbiont intracellularis

Porcine proliferative enteropathy is consistently associated with the presence of intracellular curved bacteria in epithelial cells in affected portions of intestine. Two strains of these intracellular bacteria were cultured in a cell culture system with rat enterocytes (IEC-18) and passaged several times and used as oral inocula for 14 gnotobiotic and 8 conventional pigs. DNA and immunological studies had identified these bacteria as belonging to a new taxon, Ileal symbiont (IS) intracellularis. Conventional pigs dosed with approximately 3.7 x 10(6) of these organisms passaged six times in cell culture developed severe lesions of proliferative enteropathy in the ileum. Other conventional pigs dosed with a lower titer or with organisms passaged 13 times developed moderate and minor lesions, respectively. All gnotobiotic pigs dosed with organisms failed to develop lesions. Control pigs, eight conventional and two gnotobiotic, dosed with diluent, uninfected cell material or left undosed failed to develop lesions also. Reisolation of IS intracellularis and demonstration of the organism in mucosal and fecal samples only occurred in conventional pigs dosed with organisms. Gnotobiotic pigs lacking a normal intestinal flora have not been shown to be colonized by the organism. Seroconversion to IS intracellularis or mucosal infiltration by inflammatory cells was not observed in experimentally affected pigs, confirming the weak immune response characteristic of the natural disease. These results support the identification of IS intracellularis as an etiological agent of proliferative enteropathy in pigs.

Enhanced detection of intracellular organism of swine proliferative enteritis, ileal symbiont intracellularis, in feces by polymerase chain reaction

A sensitive assay based on amplification of a 319-bp DNA fragment of the intracellular bacterium of swine proliferative enteritis was developed for the detection of the organism in the feces of swine. A vernacular name, ileal symbiont intracellularis (IS-intracellularis), has recently been published for the intracellular bacterium, which was formerly known as a Campylobacter-like organism (C.J. Gebhart, S.M. Barnes, S. McOrist, G.F. Lin, and G.H.K. Larson, Int. J. Syst. Bacteriol. 43:533-538, 1993). As few as 10(1) IS-intracellularis organisms purified from intestinal mucosa, or 10(3) IS-intracellularis per g of feces, were detected. No amplification product was produced from a polymerase chain reaction performed on DNA extracted from the feces of healthy pigs. A 319-bp DNA fragment specific for IS-intracellularis was produced on amplification of DNA from the feces of pigs with experimental and naturally occurring proliferative enteritis.

Intracellular bacteria of porcine proliferative enteropathy: cultivation and maintenance in vitro

An obligate intracellular bacterium was isolated from the intestines of all 10 cases of porcine proliferative enteropathy from four different pig farms. The organism grew in a rat enterocyte cell line (IEC-18) and was maintained over 20 passages. The growth of the bacteria was assessed by immunostaining of cells exposed to infection. Infection was not associated with morphological cell change, and growth was confined to cells infected at the time of each transfer of infection and the progeny of these cells. The bacterium is a microaerophilic, cell dependent, curved or rod-shaped, gram-negative bacillus that multiplies freely in the enterocyte cytoplasm. Cell cultures containing the intracellular bacteria appear to be free of other microorganisms, including chlamydiae and viruses.

Immunocytological responses in porcine proliferative enteropathies

The ileum, colon, and mesenteric lymph nodes of pigs naturally affected by either of the two major forms of proliferative enteropathy, namely, intestinal adenomatosis or hemorrhagic enteropathy, were examined for immunocytological responses to infection by immunocytochemistry, using antibodies directed against elements of the porcine immune system. In both forms, there was mucosal proliferation of immature enterocytes which lacked substantial major histocompatibility complex class II expression and a marked accumulation of immunoglobulin A (IgA) at the apical cytoplasm of affected enterocytes in association with intracellular Campylobacter-like organisms. In intestinal adenomatosis, there was only a mild infiltration of CD8+ and CD25+ T cells in the intestinal lamina propria. In hemorrhagic enteropathy, there was a moderate infiltration of CD8+ and CD25+ T cells and IgM+ B cells in the lamina propria. In rats and humans, villous enterocytes are thought to act as antigen-presenting cells, with major histocompatibility complex class II molecules present on their surface, capable of initiating a T-cell response (particularly of CD8+ T cells) in response to bacterial antigens. Therefore, the selection of immature crypt cells by the intracellular Campylobacter-like organisms for entry and multiplication may represent a remarkable microbial adaptation associated with local immunomodulation and enhanced bacterial survival. The accumulation of IgA within affected enterocytes may represent a reduced capability of the cells to process nonspecific IgA or an accumulation of specific IgA.