Multiplex polymerase chain reaction for simultaneous detection of Lawsonia intracellularis, Serpulina hyodysenteriae, and salmonellae in porcine intestinal specimens

Review of methods for the detection of Lawsonia intracellularis infection in pigs

Lawsonia intracellularis is an obligate intracellular bacterium associated with enteric disease in pigs. Clinical signs include weight loss, diarrhea, and, in some cases, sudden death. The hallmark lesion is the thickening of the intestinal mucosa caused by increased epithelial cell replication, known as proliferative enteropathy. The immune response to L. intracellularis is not well defined, and detection of the infection, especially in the early stages, is still a significant challenge. We review here the main approaches used to identify this important but poorly understood pathogen. Detection of L. intracellularis infection as the cause of clinical disease is confounded by the high prevalence of the pathogen in many countries and that several other pathogens can produce similar clinical signs. A single L. intracellularis–specific ELISA and several amplification assays are available commercially to aid detection and surveillance, although histopathology remains the primary way to reach a conclusive diagnosis. There are major gaps in our understanding of L. intracellularis pathogenesis, especially how the host responds to infection and the factors that drive infection toward different clinical outcomes. Knowledge of pathogenesis will increase the predictive value of antemortem tests to guide appropriate interventions, including identification and treatment of subclinically affected pigs in the early stages of disease, given that this important manifestation reduces pig productivity and contributes to the economic burden of L. intracellularis worldwide.

MALDI-TOF MS analysis of human and animal Brachyspira species and benefits of database extension

Spirochaetes belonging to the genus Brachyspira are anaerobic bacteria that colonize the large intestine of humans and animals, mainly pigs. The main species are namely, B. hyodysenteriae, the etiological agent of swine dysentery, B. pilosicoli, a zoonotic agent causing colonic spirochaetosis both in humans and different animal species, B. aalborgi, exclusively infecting humans causing colonic spirochaetosis, B. intermedia, a potential animal pathogen, B. innocens and B. murdochii, generally commensal of pigs, and B. alvinipulli, found in egg laying hens with diarrhea. In this study, for the first time, MALDI-TOF MS was applied on Brachyspira strains of human and animal origins, supplementing the existing database, limited to the species B. murdochii only, with spirochaetal protein profiles and demonstrating its usefulness in the rapid, cheap and reliable identification of Brachyspira strains at the species level, overcoming the problems previously encountered in the identification of these spirochaetes when using biochemical and genetic-based methods. Moreover, a dendrogram based on protein profiles of the different spirochaetal species was generated reflecting their host spectrum, showing in the same branch the only two species able to infect humans (B. aalborgi and B. pilosicoli) and in the other branch the spirochaetes infecting exclusively animals.

Diagnostic performance of different fecal Lawsonia intracellularis-specific polymerase chain reaction assays as diagnostic tests for proliferative enteropathy in pigs: a review

Traditionally, diagnosis of Lawsonia intracellularis-associated proliferative enteropathy (PE) has depended on necropsy and histology. Since the establishment of the etiologic role of L. intracellularis, a number of specific polymerase chain reaction (PCR) assays have been developed for the detection of DNA in feces. The present article is a systematic review of peer-reviewed publications on the application of L. intracellularis-specific fecal PCR as an antemortem diagnostic test for histologic lesions of PE in pigs. Based on this information, a range of diagnostic sensitivities (36-100%) and specificities (50-100%) of the published tests was calculated. Validity and confidence limits of the estimates varied considerably. The positive and negative predictive values of 6 different PCR assays were calculated for PE prevalence of 15%, 30%, 45%, 60%, 75%, and 90%, using a histologic case definition of PE and based on the reported test sensitivities and specificities. The simulated predictive values suggested that applying the fecal PCR assay as a diagnostic test is more likely to overestimate than underestimate the number of pigs having histologic lesions of PE under field conditions.

Ecological characterization of the colonic microbiota of normal and diarrheic dogs

We used terminal restriction fragment polymorphism (T-RFLP) analysis to assess (1) stability of the fecal microbiota in dogs living in environments characterized by varying degrees of exposure to factors that might alter the microbiota and (2) changes in the microbiota associated with acute episodes of diarrhea. Results showed that the healthy canine GI tract harbors potential enteric pathogens. Dogs living in an environment providing minimal exposure to factors that might alter the microbiota had similar microbiotas; the microbiotas of dogs kept in more variable environments were more variable. Substantial changes in the microbiota occurred during diarrheic episodes, including increased levels of Clostridium perfringens, Enterococcus faecalis, and Enterococcus faecium. When diet and medications of a dog having a previously stable microbiota were changed repeatedly, the microbiota also changed repeatedly. Temporal trend analysis showed directional changes in the microbiota after perturbation, a return to the starting condition, and then fluctuating changes over time.

Prevalence of selected enteropathogenic bacteria in Hungarian finishing pigs

The aim of this study was to obtain prevalence estimates about the most important enteropathogenic bacteria: Lawsonia intracellularis, Brachyspira hyodysenteriae, Brachyspira pilosicoli, Salmonella enterica and Clostridium perfringens A and C in Hungarian farrow-to-finish pig herds. A total of 31 herds were selected, from where six pooled faecal samples, each containing three individual rectal faecal samples were collected from fattening pigs of 5-6 months of age. All 186 samples were examined by polymerase chain reaction (PCR) for the presence of the pathogens mentioned above. Lawsonia intracellularis was found in 29 herds (93.55%) and in 108 samples (58.06%); B. hyodysenteriae in 14 herds (45.16%) and in 23 samples (12.37%); B. pilosicoli in 19 herds (61.29%) and in 53 samples (28.49%); S. enterica in 17 herds (54.83%) and in 40 samples (21.50%). We detected the presence of C. perfringens A in 19 herds (61.29%) and in 46 samples (24.73%), while C. perfringens C was found in 8 herds (25.81%) and in 11 samples (5.91%). All examined herds were infected with one or more of these agents. Herds with diarrhoea in the mid- to late finishing phase had almost 10 times higher prevalence of B. hyodysenteriae than herds without such a history.

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.

Isolation of Lawsonia intracellularis in Korea and reproduction of proliferative enteropathy in pigs and hamsters

Lawsonia intracellularis (L. intracellularis) was isolated from a Korean pig suffering acute proliferative enteropathy. In vitro culture conditions of L. intracellularis were established in McCoy cells. Pigs and hamsters experimentally infected with the pure culture of L. intracellularis reproduced clinical signs and intestinal lesions of proliferative enteropathy. The presence of L. intracellularis in the intestinal lesions was confirmed by immunohistochemistry with L. intracellularis-specific monoclonal antibodies.

Comparative evaluation of molecular assays for the identification of intestinal spirochaetes from diseased pigs

Rapid identification of porcine Brachyspira species is required in order to differentiate pathogenic from non-pathogenic species. The aim of our study was to compare a recently described genetic method based on polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP), nox RFLP-PCR assay, and three species-specific PCRs described previously in the literature with a 16S rRNA gene RFLP-PCR discriminatory reference assay (16S RFLP-PCR) for the identification of Brachyspira spp. of swine origin. In this study, 20 porcine spirochaetal strains were identified and compared to 33 reference strains by 16S RFLP-PCR and nox RFLP-PCR and three species-specific PCRs. RFLP-PCR methods showed concordant results for 47 strains and discordances for 6 strains (2 differently identified and 4 not revealed by nox RFLP-PCR). In our hands species-specific PCRs showed concordant results with 16S and nox RFLP-PCR for 43 strains and discordances for 10 strains (2 differently identified and 8 not amplified). The same results observed testing the 20 field-isolated spirochaetes were obtained for the corresponding porcine faecal samples. The detection limit was 10(2) -10(3) cells/g of faeces for 16S rRNA gene PCR and 10(4) cells/g of faeces for nox PCR. In our experience nox RFLP-PCR appeared successful for the speciation of B. hyodysenteriae reserving 16S RFLP-PCR for all other pathogenic and non-pathogenic Brachyspira species. Among the species-specific PCR assays tested only that for B. pilosicoli was useful in our hands.

The 23S rRNA gene PCR-RFLP used for characterization of porcine intestinal spirochete isolates

Using three reference strains of Brachyspira hyodysenteriae (B204, B234, B169), one B. pilosicoli (P43/6/78), one B. murdochii (56-150), one B. intermedia (PWS/A), one B. innocens (B256) and ten Korean isolates, PCR-RFLP analysis of DNA encoding 23S rRNA was performed to establish a rapid and accurate method for characterizing porcine intestinal spirochetes. Consequently, B. hyodysenteriae and B. pilosicoli revealed different restriction patterns; however, the other three species shared the same pattern. These findings are not consistent with a prior report. Differences in 23S rRNA gene sequences, between two B. murdochii strains, 56-150 and 155-20, were observed. These results indicate that 23S rRNA PCR-RFLP could be used as an identification method for pathogenic Brachyspira spp. (B. hyodysenteriae and B. pilosicoli) as well as an epidemiological tool for characterizing spirochetes isolated from swine.

Development of a multiplex-PCR for rapid detection of the enteric pathogens Lawsonia intracellularis, Brachyspira hyodysenteriae, and Brachyspira pilosicoli in porcine faeces

AIMS

To develop an assay to simultaneously detect Lawsonia intracellularis, Brachyspira hyodysenteriae and Brachyspira pilosicoli in pig faeces.

METHODS AND RESULTS

A multiplex-polymerase chain reaction (M-PCR) was designed to amplify a 655-base pair (bp) portion of the L. intracellularis 16S rRNA gene, a 354-bp portion of the B. hyodysenteriae NADH oxidase gene, and a 823-bp portion of the B. pilosicoli 16S rRNA gene. Specificity was assessed using 80 strains of Brachyspira spp. and 30 other enteric bacteria. Bacterial DNA was extracted from faeces using the QIAamp DNA Stool Mini Kit. The M-PCR was tested in parallel with culture and/or PCR on 192 faecal samples from eight piggeries. Faeces also were seeded with known cell concentrations of the three pathogenic species, and the limits of detection of the M-PCR tested. The M-PCR was specific, with limits of detection of 10(2)-10(3) cells of the respective species per gram of faeces.

CONCLUSIONS

The M-PCR is a rapid, sensitive and specific test for detecting three important enteric bacterial pathogens of pigs.

SIGNIFICANCE AND IMPACT OF THE STUDY

The availability of a new diagnostic M-PCR will allow rapid detection and control of three key porcine enteric pathogens.

Chips and SNPs, bugs and thugs: a molecular sleuthing perspective

Recent events both here and abroad have focused attention on the need for ensuring a safe and secure food supply. Although much has been written about the potential of particular select agents in bioterrorism, we must consider seriously the more mundane pathogens, especially those that have been implicated previously in foodborne outbreaks of human disease, as possible agents of bioterrorism. Given their evolutionary history, the enteric pathogens are more diverse than agents such as Bacillus anthracis, Francisella tularensis, or Yersinia pestis. This greater diversity, however, is a double-edged sword; although diversity affords the opportunity for unequivocal identification of an organism without the need for whole-genome sequencing, the same diversity can confound definitive forensic identification if boundaries are not well defined. Here, we discuss molecular approaches used for the identification of Salmonella enterica, Escherichia coli, and Shigella spp. and viral pathogens and discuss the utility of these approaches to the field of microbial molecular forensics.

A Lawsonia intracellularis transmission study using a pure culture inoculated seeder-pig sentinel model

Transmission of Lawsonia intracellularis from experimentally inoculated pigs to naive swine was demonstrated in this study. The study was conducted using conventional pigs divided into three groups as follows: principles inoculated with L. intracellularis, sentinels, and controls. The pigs were inoculated and paired on 13 and 9 days post-inoculation with a sentinel pig for 7 days. Fecal samples and serum samples were collected throughout the study for polymerase chain reaction (PCR) and antibody testing by indirect fluorescent antibody techniques. After co-mingling, the inoculated group was necropsied; sentinel and control pigs were necropsied 7-14 days later. The intestinal tracts were evaluated grossly and microscopically for lesions. PCR was performed on intestinal mucosal scrapings and feces. Warthin-Starry and fluorescent antibody staining procedures were conducted to confirm colonization with L. intracellularis. Gross and microscopic lesions typical of porcine proliferative enteropathy (PPE) were observed in both the inoculated and sentinel groups. Transmission was demonstrated from inoculated principle pigs to sentinel pigs. PCR results detected cyclical shedding of L. intracellularis in the feces. Seroconversion occurred in pigs that were exposed to L. intracellularis. From this study, it was demonstrated that transmission of L. intracellularis can occur easily in an environment with experimentally infected pigs and that PCR can be a useful tool to monitor fecal shedding of the organism.

Comparison of diagnostic techniques for porcine proliferative enteropathy (Lawsonia intracellularis infection)

In studying the post-mortem diagnosis of porcine proliferative enteropathy (PPE) a "double-blind" study was performed on 77 apparently healthy "finisher" pigs at the time of slaughter, to compare the results of a polymerase chain reaction (PCR) technique with those of (1) an indirect immunofluorescence assay (IFA), (2) examination for gross proliferative lesions at slaughter, (3) histopathological study of sections stained with haematoxylin and eosin (HE), and (4) Warthin-Starry (WS) silver staining for intracellular bacteria. The IFA, with a sensitivity of 89% and a specificity of 97% (positive "likelihood ratio"=30) and an agreement of 82% with PCR, is suggested as an alternative to the PCR in the post-mortem diagnosis of PPE. Histopathological examination was shown to be of little use as a principal diagnostic method, although it appeared to be effective in diagnosing infection by Lawsonia intracellularis in cases with proliferative-type lesions (positive likelihood ratio=29.6). Finally, the values obtained from an examination of gross lesions (k=0.075; positive likelihood ratio of 1.3) and WS staining (k=0.42; positive likelihood ratio of 5.3) demonstrated the lack of validity of these tests for the diagnosis of L. intracellularis infection.

Development of a duplex PCR assay for detection of Brachyspira hyodysenteriae and Brachyspira pilosicoli in pig feces

A duplex PCR (D-PCR) amplifying portions of the Brachyspira hyodysenteriae NADH oxidase gene and the B. pilosicoli 16S rRNA gene was developed and then tested on DNA extracted from 178 porcine fecal samples. The feces also underwent anaerobic culture and species-specific PCRs. Fecal extraction-D-PCR detected seven additional samples containing B. hyodysenteriae and five more containing B. pilosicoli.

Comparison of cultivation and PCR-hybridization for detection of Salmonella in porcine fecal and water samples

A total of 150 fecal and water samples from four swine farms were tested for the presence of Salmonella enterica using different enrichment techniques as follows: (i) 92 fecal samples from nursery and farrowing barns at three swine farms were preenriched overnight in tryptic soy broth (TSB) at 37 degrees C followed by overnight enrichment in Rappaport-Vassiliadis 10 broth (RV10) at 42 degrees C; (ii) 24 water samples from the third farm were preenriched overnight in 3MC broth at 37 degrees C followed by overnight enrichment in RV10 at 42 degrees C; and (iii) 34 fecal samples from a fourth farm, a finishing farm, were enriched overnight in RV10 at 42 degrees C with no additional enrichment. Following each of the enrichment techniques, samples were subcultured onto modified semisolid Rappaport-Vassiliadis (MSRV) agar prior to transfer to Hektoen Enteric agar plates for the recovery of viable Salmonella bacteria. Presumptive Salmonella isolates were biochemically and serologically confirmed. For the PCR detection of Salmonella, a 1-ml portion was removed from each sample after the first overnight enrichment and the DNA was extracted using a Sepharose CL-6B spin column. Amplicons (457 bp) derived from primers to the invA and invE genes were confirmed as Salmonella specific on ethidium bromide-stained agarose gels by Southern hybridization with a 20-mer oligonucleotide probe specific for the Salmonella invA gene. Neither the standard microbiological method nor the molecular method detected all of the 65 samples that tested positive by both methods or either method alone. Salmonella bacteria were detected by both cultivation and PCR-hybridization in 68% (17 of 25) of the positive samples that were preenriched in TSB, in 73% (11 of 15) of the positive samples preenriched in 3MC broth, and in 24% (6 of 25) of the positive samples enriched in RV10. Agreement between Salmonella detection using cultivation with preenrichment and detection by PCR was 76% using the kappa statistic. However, agreement between Salmonella detection using cultivation without preenrichment and detection by PCR was about 6%; the PCR assay detected 80% (20 of 25) of the 25 positive samples, while Salmonella bacteria were recovered from only 44% (11 of 25) by cultivation. Our results indicate that the PCR-hybridization approach is equivalent to or better than cultivation for detecting Salmonella in swine feces or water samples from swine farms when using the medium combinations evaluated in this study.

Improved diagnosis of porcine proliferative enteropathy caused by Lawsonia intracellularis using polymerase chain reaction-enzyme-linked oligosorbent assay (PCR-ELOSA)

Proliferative enteropathy (PE) caused by Lawsonia intracellularis is a major diarrheal disease affecting swine worldwide. Routine laboratory diagnosis of PE is done by amplification of L. intracellularis -specific DNA sequences by PCR followed by agarose gel electrophoresis and staining of PCR products with ethidium bromide. We report the development of an enzyme-linked oligosorbent assay (ELOSA) for specific identification of chromosomal L. intracellularis 328-bp PCR amplified products. The ELOSA involved determination of optical density value at 450 nm (OD(450)) after hybridization of biotin-labelled PCR products with an amine-modified internal oligonucleotide capture probe immobilized in microwell plates, and avidin-biotin-peroxidase complex. A positive ELOSA cut-off value of > or =0.375 was established using the mean OD(450)of negative control specimens plus three times the standard deviation. Using this value, the detection limit of PCR amplified L. intracellularis -specific products by ethidium bromide-stained agarose gel electrophoresis, Southern blot, and ELOSA were estimated to be 6.1 ng, between 0.8 and 3.0 ng, and 0.8 ng of DNA, respectively. Comparison of ethidium bromide-stained agarose gel analysis with ELOSA for detection of L. intracellularis -specific PCR products from 315 clinical specimens revealed 78% sensitivity, 100% specificity and 94% accuracy. The ELOSA produced a spectrophotometric signal that confirmed the authenticity of PCR products without subjective interpretation of ethidium bromide-stained PCR products after agarose gel electrophoresis.

Diarrhea in growing-finishing swine

Regardless of the etiology of an enteric disease in nursery age to finisher swine, making a prompt and accurate diagnosis is crucial. Eliciting a complete history, assessing clinical signs and pathology, and selecting and interpreting laboratory tests are essential components in achieving this. Early detection and diagnosis of enteric disease is particularly critical in the nursery through finisher phase because of economic impacts. Recurrent topics when discussing control and prevention of enteric diseases are reducing stress and improving pig comfort and reducing or eliminating exposure through sanitation and biosecurity. These are not new concepts; in fact, prior to the advent of antimicrobials, they were the mainstay of treatment of enteric diseases. With concern over the use of antimicrobials in food animal production increasing, exploiting disease ecology to control enteric diseases is increasing in importance. New vaccines and bacterins for postweaning swine enteric diseases are needed tools to exploit the pig's immune system. Recent advances in diagnostic capabilities allow an increase in understanding and exploitation of disease ecology.

Differentiation of Serpulina species by NADH oxidase gene (nox) sequence comparisons and nox-based polymerase chain reaction tests

The NADH oxidase genes (nox) of 18 strains of intestinal spirochaetes were partially sequenced over 1246 bases. Strains examined included 17 representatives from six species of the genus Serpulina, and the type strain 513A(T) of the human intestinal spirochaete Brachyspira aalborgi. Sequences were aligned and used to investigate phylogenetic relationships between the organisms. Nox sequence identities between strains within the genus Serpulina were within the range 86.3-100%, whilst the nox gene of B. aalborgi shared between 78.8-83.0% sequence identity with the nox sequences of the various Serpulina strains. A phenogram produced based on sequence dissimilarities was in good agreement with the current classification of species in the genus Serpulina, although an atypical strongly beta-haemolytic porcine strain (P280/1), previously thought to be S. innocens, appeared distinct from other members of this species. Primer pairs were developed from the nox sequence alignments for use in polymerase chain reaction (PCR) identification of the pathogenic species S. hyodysenteriae (NOX1), S. intermedia (NOX2), and S. pilosicoli (NOX3), and for the combined non-pathogenic species S. innocens and S. murdochii (NOX4). The PCRs were optimised using 80 strains representing all currently described species in the genus Serpulina, as well as the type strain of B. aalborgi. Tests NOX1 and NOX4 specifically amplified DNA from all members of their respective target species, whilst tests NOX2 and NOX3 were less sensitive. NOX2 amplified DNA from all 10 strains of S. intermedia from pigs but from only 4 of 10 strains from chickens, whilst NOX3 amplified DNA from only 18 of 21 S. pilosicoli strains, even at low stringency. Tests NOX1 and NOX4 should prove useful in veterinary diagnostic laboratories, whilst NOX2 and NOX3 require further refinement.

Detection of Lawsonia intracellularis in swine using polymerase chain reaction methodology

The polymerase chain reaction (PCR) was evaluated for its usefulness as a diagnostic tool to detect Lawsonia (ileal symbiont) intracellularis. Porcine ilea were collected from swine cases submitted to the Iowa State University Veterinary Diagnostic Laboratory between December 1, 1994, and June 30, 1995. Sampling was random, with no regard to health status. There were 621 ileum scrapings evaluated using the PCR technique. Thirty-five of the samples were positive, either by PCR or conventional diagnostic methods such as histology and Warthin-Starry silver stain. These 35 samples were further evaluated by Warthin-Starry silver stain and indirect immunofluorescent antibody test (IFAT) to confirm the presence of L. intracellularis in the tissue sections. Of the 26 samples positive by PCR, 22 were positive by IFAT. Sixteen of the 22 were also positive when stained with Warthin-Starry and evaluated microscopically for typical bacteria. Nine of the original samples were negative by all 3 techniques. PCR appears more sensitive and specific for L. intracellularis detection than Warthin-Starry stain and IFAT. This study provides evidence that PCR may be useful as a reference standard for the detection of L. intracellularis. PCR may be an appropriate monitoring tool for swine herds because it is a rapid procedure that could be applied to batch testing. Although the test is currently too laborious and expensive for routine diagnostic use, there may be situations in which it is justified because of the advantages of greater sensitivity and specificity.