The intestinal spirochete Brachyspira pilosicoli attaches to cultured Caco-2 cells and induces pathological changes

T-independent B-cell effect of agents associated with swine grower-finisher diarrhea

Swine dysentery, spirochetal colitis, and salmonellosis are production-limiting enteric diseases of global importance to the swine industry. Despite decades of efforts, mitigation of these diseases still relies on antibiotic therapy. A common knowledge gap among the 3 agents is the early B-cell response to infection in pigs. Thus, this study aimed to characterize the porcine B-cell response to Brachyspira hyodysenteriae, Brachyspira hampsonii (virulent and avirulent strains), Brachyspira pilosicoli, and Salmonella Typhimurium, the agents of the syndromes mentioned above. Immortalized porcine B-cell line derived from a crossbred pig with lymphoma were co-incubated for 8 h with each pathogen, as well as E. coli lipopolysaccharide (LPS) and a sham-inoculum (n = 3/treatment). B-cell viability following treatments was evaluated using trypan blue, and the expression levels of B-cell activation-related genes was profiled using reverse transcription quantitative PCR. Only S. Typhimurium and LPS led to increased B-cell mortality. B. pilosicoli downregulated B-lymphocyte antigen (CD19), spleen associated tyrosine Kinase (syk), tyrosine-protein kinase (lyn), and Tumour Necrosis Factor alpha (TNF-α), and elicited no change in immunoglobulin-associated beta (CD79b) and swine leukocyte antigen class II (SLA-DRA) expression levels, when compared to the sham-inoculated group. In contrast, all other treatments significantly upregulated CD79b and stimulated responses in other B-cell downstream genes. These findings suggest that B. pilosicoli does not elicit an immediate T-independent B-cell response, nor does it trigger antigen-presenting mechanisms. All other agents activated at least one trigger within the T-independent pathways, as well as peptide antigen presenting mechanisms. Future research is warranted to verify these findings in vivo.

In Vitro Porcine (Explant) Colon Culture

Models have been extensively used to investigate disease pathogenesis. Animal models are costly and require extensive logistics for animal care, and samples are not always suitable for different analytical techniques or to answer the research question. In vitro cell culture models are generally focused on recreating a specific characteristic of an organ and are limited to a single cell population that does not display the characteristic tissue architecture of the source organ. In addition, such models do not account for the many interactions between pathogens and the diverse cell subsets that are normally present in a given organ. Conclusions based on conventional 2D cell culture methods are limited, requiring extrapolation from a reductionist model to understand in vivo events. In vitro organ culture (IVOC) offers a way to overcome some of these limitations. Explants conserve important in vivo characteristics, such as different cell types and complex tissue architecture. This in vitro (ex vivo) organ culture protocol of the swine large intestine aims at maintaining viable colonic mucosa for up to 5 days. The protocol described herein applies a combination of methods used for immortalized cell culture and stem cell stimulation to support the physiological cellular flow inherent of the intestinal mucosa. Required equipment includes a hyperoxic chamber and culture at the air-liquid interface.

BPP43_05035 is a Brachyspira pilosicoli cell surface adhesin that weakens the integrity of the epithelial barrier during infection

The anaerobic spirochete Brachyspira causes intestinal spirochetosis, characterized by the intimate attachment of bacterial cells to the colonic mucosa, potentially leading to symptoms such as diarrhea, abdominal pain, and weight loss. Despite the clinical significance of Brachyspira infections, the mechanism of the interaction between Brachyspira and the colon epithelium is not known. We characterized the molecular mechanism of the B. pilosicoli-epithelium interaction and its impact on the epithelial barrier during infection. Through a proteomics approach, we identified BPP43_05035 as a candidate B. pilosicoli surface protein that mediates bacterial attachment to cultured human colonic epithelial cells. The crystal structure of BPP43_05035 revealed a globular lipoprotein with a six-bladed beta-propeller domain. Blocking the native BPP43_05035 on B. pilosicoli, either with a specific antibody or via competitive inhibition, abrogated its binding to epithelial cells, which required cell surface-exposed N-glycans. Proximity labeling and interaction assays revealed that BPP43_05035 bound to tight junctions, thereby increasing the permeability of the epithelial monolayer. Extending our investigation to humans, we discovered a downregulation of tight junction and brush border genes in B. pilosicoli-infected patients carrying detectable levels of epithelium-bound BPP43_05035. Collectively, our findings identify BPP43_05035 as a B. pilosicoli adhesin that weakens the colonic epithelial barrier during infection.

Alteration of Colonic Mucin Composition and Cytokine Expression in Acute Swine Dysentery

Swine dysentery (SD) is an enteric disease associated with strongly β-hemolytic Brachyspira spp. that cause mucohemorrhagic diarrhea primarily in grower-finisher pigs. We characterized alteration of colonic mucin composition and local cytokine expression in the colon of pigs with acute SD after B. hyodysenteriae (Bhyo) infection and fed either a diet containing 30% distillers dried grains with solubles (DDGS) or a control diet. Colonic tissue samples from 9 noninoculated pigs (Control, N = 4; DDGS, N = 5) and 10 inoculated pigs experiencing acute SD (Bhyo, N = 4; Bhyo-DDGS, N = 6) were evaluated. At the apex of the spiral colon, histochemical staining with high-iron diamine-Alcian blue revealed increased sialomucin (P = .008) and decreased sulfomucin (P = .027) in Bhyo pigs relative to controls, with a dietary effect for sulfomucin. Noninoculated pigs fed DDGS had greater expression of sulfomucin (P = .002) compared to pigs fed the control diet. Immunohistochemically, there was de novo expression of mucin 5AC (MUC5AC) in the Bhyo group while mucin 2 (MUC2) expression was not significantly different between groups. RNA in situ hybridization to detect the pro-inflammatory cytokine IL-1β often showed increased expression in the Bhyo group although without statistical significance, and this was not correlated with MUC5AC or MUC2 expression, suggesting IL-1β is not a major regulator of their secretion in acute SD. Expression of the anti-inflammatory cytokine TGF-β1 was significantly suppressed in the Bhyo group compared to controls (P = .005). This study reveals mucin and cytokine alterations in the colon of pigs with experimentally induced SD and related dietary effects of DDGS.

Impairment of electroneutral Na+ transport and associated downregulation of NHE3 contributes to the development of diarrhea following in vivo challenge with Brachyspira spp

The effect of Brachyspira hyodysenteriae and Brachyspira hampsonii spirochetosis on Na⁺ transport was assessed in the colon to determine its contribution to diarrheal disease in pigs following experimental infection. Electrogenic and electroneutral Na⁺ absorption was assessed in Ussing chambers by radiolabeled ²²Na flux and pharmacological inhibitory studies. Basal radiolabeled ²²Na flux experiments revealed that mucosal-to-serosal flux (J_ms) was significantly impaired in B. hyodysenteriae and B. hampsonii-diseased pigs. Inhibition of epithelial sodium channel via amiloride did not significantly reduce electrogenic short-circuit current (I_sc) in the proximal, apex, and distal colonic segments of diseased pigs over control pigs, suggesting that a loss of electroneutral Na⁺ absorption is responsible for diarrheal development. These findings were further supported by significant downregulation of Na⁺/H⁺ exchanger (NHE1, NHE2, and NHE3) mRNA expression in the proximal, apex, and distal colonic segments paired with decreased protein expression of the critical NHE3 isoform. The decrease in NHE3 mRNA expression appears not to be attributed to the host's cytokine response as human IL-1α did not modify NHE3 mRNA expression in Caco-2 cells. However, a whole cell B. hampsonii lysate significantly downregulated NHE3 mRNA expression and significantly increased p38 phosphorylation in Caco-2 cells. Together these findings provide a likely mechanism for the spirochete-induced malabsorptive diarrhea, indicated by a decrease in electroneutral Na⁺ absorption in the porcine colon due to Brachyspira's ability to inhibit NHE3 transcription, resulting in diarrheal disease.NEW & NOTEWORTHY This research demonstrates that diarrheal disease caused by two infectious spirochete spp. is a result of impaired electroneutral Na⁺ absorption via Na⁺/H⁺ exchanger 3 (NHE3) in the porcine colon. Our findings suggest that the decrease in NHE3 mRNA and protein is not likely a result of the host's cytokine response. Rather, it appears that these two Brachyspira spp. directly inhibit the transcription and translation of NHE3, resulting in the development of diarrhea.

Severe Human Intestinal Spirochetosis: An Unusual Cause of Diffuse Colonic Ulcerations in a Patient Living with HIV

We describe a case of a homosexual male with human immunodeficiency virus (HIV) and CD4 count of 246 presenting with acute severe bloody diarrhea. Infectious work up was negative, and colonoscopy revealed severe diffuse colonic ulcerations. Histopathologic analysis and Treponemal pallidum immunostaining confirmed the diagnosis of intestinal spirochetosis. There was no evidence of co-infection with other pathogens. His symptoms completely resolved after a 14-day course of metronidazole. This case is notable as colonic ulceration of any severity in patients living with HIV is rarely identified with intestinal spirochetosis. Hence, it should be considered in the differential diagnosis of colonic ulcerations.

Decreased electrogenic anionic secretory response in the porcine colon following in vivo challenge with Brachyspira spp. supports an altered mucin environment

Brachyspira spp. cause diarrheal disease in multiple animal species by colonization of the colon, resulting in colitis, mucus induction, and disrupted ion transport. Unique to spirochete pathogenesis is the immense production of mucus, resulting in a niche mucin environment likely favoring spirochete colonization. Mucin rheological properties are heavily influenced by anionic secretion, and loss of secretory function has been implicated in diseases such as cystic fibrosis. Here, the effects on the agonist-induced electrogenic anionic secretory response by infectious colonic spirochete bacteria Brachyspira hyodysenteriae and Brachyspira hampsonii were assessed in the proximal, apex, and distal sections of colon in Ussing chambers. Activation of secretion via isoproterenol, carbachol, and forskolin/3-isobutyl-1-methylxanthine demonstrated a significantly decreased change in short-circuit current ( I_sc) in Brachyspira-infected pigs in all sections. Tissue resistances did not account for this difference, rather, it was attributed to a decrease in anionic secretion as indicated by a decrease in bumetanide inhibitable I_sc. Quantitative RT-PCR and Western blot analyses determined that the major anionic channels of the epithelium were downregulated in diarrheic pigs paired with altered mucin gene expression. The investigated cytokines were not responsible for the downregulation of anion channel gene transcripts. Although IL-1α was upregulated in all segments, it did not alter cystic fibrosis transmembrane conductance regulator (CFTR) mRNA expression in Caco-2 monolayers. However, a whole cell Brachyspira hampsonii lysate significantly reduced CFTR mRNA expression in Caco-2 monolayers. Together, these findings indicate that these two Brachyspira spp. may directly cause a decreased anionic secretory response in the porcine colon, supporting an altered mucin environment likely favoring spirochete colonization. NEW & NOTEWORTHY This research demonstrates for the first time that the niche mucin environment produced by two infectious spirochete spp. is supported by a decrease in the electrogenic anionic secretory response throughout the porcine colon. Our findings suggest that the host's cytokine response is not likely responsible for the decrease in anionic secretory function. Rather, it appears that Brachyspira spp. directly impede ion channel transcription and translation, potentially altering colonic mucin rheological properties, which may favor spirochete colonization.

In Vitro Porcine Colon Culture

Models have been extensively used to investigate disease pathogenesis. Animal models are costly, require extensive logistics for animal care, and samples are not always suitable for different analytical techniques or to answer the research question. In vitro cell culture models are generally focused on recreating a specific characteristic of an organ, and are limited to a single cell population that does not display the characteristic tissue architecture of the source organ. In addition, such models do not account for the many interactions between pathogens and the diverse cell subsets that are normally present in a given organ. Conclusions based on conventional 2D cell culture methods are limited, requiring extrapolation from a reductionist model to understand in vivo events. In vitro organ culture (IVOC) offers a way to overcome some of these limitations. Explants conserve important in vivo characteristics, such as different cell types and complex tissue architecture. This in vitro (ex vivo) organ culture protocol of the swine large intestine aims at maintaining viable colonic mucosa for up to 5 days. The protocol described herein applies a combination of methods used for immortalized cell culture and stem cell stimulation to support the physiological cellular flow inherent of the intestinal mucosa. Required equipment includes a hyperoxic chamber and culture at the air-liquid interface.

Impact of Brachyspira hyodysenteriae on intestinal amino acid digestibility and endogenous amino acid losses in pigs

Brachyspira hyodysenteriae (Bhyo) induces mucohemorrhagic diarrhea in pigs and is an economically significant disease worldwide. Our objectives were to determine the impact of Bhyo on apparent total tract digestibility (ATTD), ileal digestibility (AID), and ileal basal endogenous losses (BEL) in grower pigs. In addition, we assessed the effect of Bhyo on hindgut disappearance of DM, N, and GE. Thirty-two Bhyo negative gilts (38.6 ± 0.70 kg BW) were fitted with a T-cannula in the distal ileum and individually penned. In replicates 1 and 2, pigs were fed a complete diet (7 Bhyo-, 10 Bhyo+ pigs) or nitrogen-free diet (NFD; 4 Bhyo-, 11 Bhyo+ pigs), respectively. Across multiple rooms, the 21 Bhyo+ pigs (62.6 ± 1.39 kg BW) were inoculated with Bhyo on day post inoculation (dpi) 0, and the 11 Bhyo- pigs were sham inoculated. Feces were collected from 9 to 11 dpi and ileal digesta collected from 12 to 13 dpi. All pigs were euthanized at 14 to 15 dpi and intestinal tract pathology assessed. Within the complete diet and NFD treatments, data were analyzed to determine pathogen effects. All Bhyo- pigs remained Bhyo negative, and 5 Bhyo+ pigs in each replicate were confirmed Bhyo positive within 9 dpi. Infection with Bhyo reduced ATTD of DM, N, and GE and increased AID of Gly (P < 0.05). No other AA AID differences were observed. Only BEL of Pro was reduced (P < 0.05) while Arg, Trp, and Gly tended (P < 0.10) to be reduced in Bhyo+ pigs. When calculated from AID and BEL, Bhyo infection reduced standardized ileal digestibility (SID) of N, Arg, Lys, Ala, Gly, Pro, and Ser (P < 0.05) and tended to reduce Thr SID (P = 0.09). In the hindgut of Bhyo+ pigs, there was generally an appearance of nutrients rather than disappearance. In Bhyo+ pigs fed a complete diet, hindgut appearance of N and GE were increased (P < 0.05) by 58 and nine-fold, respectively, and DM tended to be increased two-fold (P = 0.06). Similarly, in NFD fed pigs, hindgut appearance of N and GE was increased by 172% and 162%, respectively, although high variability led to no significance. Altogether, Bhyo infection decreases ATTD but has minimal impact on AID of AA, when corrected for BEL, SID of N, Arg, Lys and some nonessential AA are specifically reduced. Unexpectedly, BEL of several AA involved in mucin production were unaffected by Bhyo infection. This may suggest an increased need for specific AA and energy during a Bhyo challenge.

Human intestinal spirochetosis mimicking ulcerative colitis

Human intestinal spirochetosis (HIS) is a colorectal infection caused by the Brachyspira species of intestinal spirochetes, whose pathogenicity in humans remains unclear owing to the lack of or mild symptoms. We monitored the 5-year clinical course of a woman diagnosed with HIS in whom ulcerative colitis (UC) had been suspected. Following a positive fecal occult blood test, she underwent a colonoscopic examination at a local clinic where she was diagnosed with "right-sided" UC concomitant with incidentally detected HIS, and was referred to our hospital. Colonoscopic, histopathological, and cytological examination revealed localized erosive colitis in the ascending and the right transverse colon concomitant with HIS resembling skip lesions of UC. Initially, we chose the wait-and-watch approach; however, she gradually developed bloody diarrhea. Metronidazole improved her abdominal symptoms, as well as her colonoscopic and histopathological findings, suggesting that HIS was responsible for her colorectal inflammation. This case reveals (1) a possible pro-inflammatory role of HIS, (2) difficulties in diagnosing HIS in chronic proctocolitis, and (3) a possible inclusion of some HIS cases in "UC". HIS could mimic UC and might be included in differential diagnoses for UC. Antibiotic administration is necessary following the detection of HIS, particularly in patients demonstrating an atypical presentation of UC.

The Spirochete Brachyspira pilosicoli, Enteric Pathogen of Animals and Humans

Brachyspira pilosicoli is a slow-growing anaerobic spirochete that colonizes the large intestine. Colonization occurs commonly in pigs and adult chickens, causing colitis/typhlitis, diarrhea, poor growth rates, and reduced production. Colonization of humans also is common in some populations (individuals living in village and peri-urban settings in developing countries, recent immigrants from developing countries, homosexual males, and HIV-positive patients), but the spirochete rarely is investigated as a potential human enteric pathogen. In part this is due to its slow growth and specialized growth requirements, meaning that it is not detectable in human fecal samples using routine diagnostic methods. Nevertheless, it has been identified histologically attached to the colon and rectum in patients with conditions such as chronic diarrhea, rectal bleeding, and/or nonspecific abdominal discomfort, and one survey of Australian Aboriginal children showed that colonization was significantly associated with failure to thrive. B. pilosicoli has been detected in the bloodstream of elderly patients or individuals with chronic conditions such as alcoholism and malignancies. This review describes the spirochete and associated diseases. It aims to encourage clinicians and clinical microbiologists to consider B. pilosicoli in their differential diagnoses and to develop and use appropriate diagnostic protocols to identify the spirochete in clinical specimens.

Infection of porcine colon explants with "Brachyspira hampsonii" leads to increased epithelial necrosis and catarrhal exudate

Mucohemorrhagic diarrhea in pigs caused by Brachyspira spp. has a global distribution, and an economic impact on affected farms due to poor performance of animals. Demonstrations that "Brachyspira hampsonii" is pathogenic have been achieved using in vivo animal models, but a critical knowledge gap exists regarding the pathogenic mechanisms employed by Brachyspira. Here, we used in vitro organ culture of porcine colon to investigate interactions between "B. hampsonii" and explants during the first 12 h of contact. Explants were either inoculated with "B. hampsonii" or sterile culture broth. Responses to infection were evaluated by optical microscopy and quantitative PCR. Significantly greater numbers of necrotic crypt cells and thicker catarrhal exudate were observed on infected explants compared to controls. Spirochaetes were observed in the mucus layer, in contact with necrotic exfoliated cells, in crypts and the lamina propria. Statistical differences were observed in mRNA levels between inoculated and control explants for IL-1α, TNF-α and ZO-1 using a Bayesian analysis, but not observed using the ΔΔCq method. These results provide a demonstration of a porcine colon explant model for investigating interactions of Brachyspira with its host and show that initial effects on the host are observed within the first 12 h of contact.

Distribution and phylogeny of Brachyspira spp. in human intestinal spirochetosis revealed by FISH and 16S rRNA-gene analysis

During six years as German National Consultant Laboratory for Spirochetes we investigated 149 intestinal biopsies from 91 patients, which were histopathologically diagnosed with human intestinal spirochetosis (HIS), using fluorescence in situ hybridization (FISH) combined with 16S rRNA gene PCR and sequencing. Aim of this study was to complement histopathological findings with FISH and PCR for definite diagnosis and species identification of the causative pathogens. HIS is characterized by colonization of the colonic mucosa of the human distal intestinal tract by Brachyspira spp. Microbiological diagnosis of HIS is not performed, because of the fastidious nature and slow growth of Brachyspira spp. in culture. In clinical practice, diagnosis of HIS relies solely on histopathology without differentiation of the spirochetes. We used a previously described FISH probe to detect and identify Brachyspira spp. in histological gut biopsies. FISH allowed rapid visualization and identification of Brachyspira spp. in 77 patients. In most cases, the bright FISH signal already allowed rapid localization of Brachyspira spp. at 400× magnification. By sequencing, 53 cases could be assigned to the B. aalborgi lineage including "B. ibaraki" and "B. hominis", and 23 cases to B. pilosicoli. One case showed mixed colonization. The cases reported here reaffirm all major HIS Brachyspira spp. clusters already described. However, the phylogenetic diversity seems to be even greater than previously reported. In 14 cases, we could not confirm HIS by either FISH or PCR, but found colonization of the epithelium by rods and cocci, indicating misdiagnosis by histopathology. FISH in combination with molecular identification by 16S rRNA gene sequencing has proved to be a valuable addition to histopathology. It provides definite diagnosis of HIS and allows insights into phylogeny and distribution of Brachyspira spp. HIS should be considered as a differential diagnosis in diarrhea of unknown origin, particularly in patients from risk groups (e.g. patients with colonic adenomas, inflammatory polyps, inflammatory bowel disease or HIV infection and in men who have sex with men).

Immunohistochemical study of mucins in human intestinal spirochetosis

Most patients with human intestinal spirochetosis (HIS; a colorectal bacterial infection caused by Brachyspira species) seem asymptomatic, and its pathogenicity remains unclear. Recently, alterations in mucin expression were reported in animal Brachyspira infection. The present question was "Is mucin expression altered in HIS?" Using antibodies for MUCs 1, 2, 4, 5AC, and 6, we immunohistochemically compared 215 specimens from 83 histology-confirmed HIS cases with 106 specimens from 26 non-HIS cases. Positive staining (which included even focal positive staining) was rated "high (+)" or "low (+)." Results were analyzed for 4 categories of lesions, and associations between MUC expression and spirochetal presence were also analyzed. In the "specimens without polyps or adenocarcinoma" category, high (+) MUC2 positivity was more frequent in HIS than in control. In the hyperplasia/serrated polyp category, in HIS (versus control), the MUC5AC positivity rate was lower, whereas high (+) MUC4 positivity was more frequent. In the conventional adenoma category, in HIS (versus control), the MUC1 positivity rate was lower, whereas both high (+) MUC2 positivity and high (+) MUC5AC positivity were less frequent. In the adenocarcinoma category, high (+) MUC2 positivity was more frequent in HIS than in control. Among the above mucins, only MUC1 positivity was significantly associated with an absence of the so-called fringe formation, an absence of spiral organisms within mucus, and an absence of strong immunopositive materials within the epithelial layer and within the subepithelial layer. The results suggest that Brachyspira infection or a related change in the microbiome may alter the large intestine mucin expression profile in humans.

Comparison of Brachyspira hyodysenteriae Isolates Recovered from Pigs in Apparently Healthy Multiplier Herds with Isolates from Herds with Swine Dysentery

Swine dysentery (SD) is a mucohaemorrhagic colitis of grower/finisher pigs classically resulting from infection by the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. This study aimed to determine whether B. hyodysenteriae isolates from pigs in three healthy German multiplier herds supplying gilts to other farms differed from isolates from nine German production herds with SD. Isolates were subjected to whole genomic sequencing, and in silico multilocus sequence typing showed that those from the three multiplier herds were of previously undescribed sequence types (ST132, ST133 and ST134), with all isolates from the same herd having the same ST. All isolates were examined for the presence of 332 genes encoding predicted virulence or virulence lifestyle associated factors, and these were well conserved. Isolates from one multiplier herd were atypical in being weakly haemolytic: they had 10 amino acid substitutions in the haemolysin III protein and five in the haemolysin activation protein compared to reference strain WA1, and had a disruption in the promoter site of the hlyA gene. These changes likely contribute to the weakly haemolytic phenotype and putative lack of virulence. These same isolates also had nine base pair insertions in the iron metabolism genes bitB and bitC and lacked five of six plasmid genes that previously have been associated with colonisation. Other overall differences between isolates from the different herds were in genes from three of five outer membrane proteins, which were not found in all the isolates, and in members of a block of six plasmid genes. Isolates from three herds with SD had all six plasmid genes, while isolates lacking some of these genes were found in the three healthy herds-but also in isolates from six herds with SD. Other differences in genes of unknown function or in gene expression may contribute to variation in virulence; alternatively, superior husbandry and better general health may have made pigs in the two multiplier herds colonised by "typical" strongly haemolytic isolates less susceptible to disease expression.

Sensitivity Analysis of an ENteric Immunity SImulator (ENISI)-Based Model of Immune Responses to Helicobacter pylori Infection

Agent-based models (ABM) are widely used to study immune systems, providing a procedural and interactive view of the underlying system. The interaction of components and the behavior of individual objects is described procedurally as a function of the internal states and the local interactions, which are often stochastic in nature. Such models typically have complex structures and consist of a large number of modeling parameters. Determining the key modeling parameters which govern the outcomes of the system is very challenging. Sensitivity analysis plays a vital role in quantifying the impact of modeling parameters in massively interacting systems, including large complex ABM. The high computational cost of executing simulations impedes running experiments with exhaustive parameter settings. Existing techniques of analyzing such a complex system typically focus on local sensitivity analysis, i.e. one parameter at a time, or a close “neighborhood” of particular parameter settings. However, such methods are not adequate to measure the uncertainty and sensitivity of parameters accurately because they overlook the global impacts of parameters on the system. In this article, we develop novel experimental design and analysis techniques to perform both global and local sensitivity analysis of large-scale ABMs. The proposed method can efficiently identify the most significant parameters and quantify their contributions to outcomes of the system. We demonstrate the proposed methodology for ENteric Immune SImulator (ENISI), a large-scale ABM environment, using a computational model of immune responses to Helicobacter pylori colonization of the gastric mucosa.

Appendiceal spirochaetosis in children

Background

Acute appendicitis is a surgical emergency in which the appendix is surgically removed to prevent peritonitis due to perforation of the appendix. Depending on age and gender, up to 17% of removed appendices do not show the histopathological changes pathognomonic for acute appendicitis and are called ‘pseudo-appendicitis’. Intestinal spirochaetes have been reported in up to 12.3% of these non-inflamed appendices obtained from adults. Although children carry the highest risk for acute appendicitis, not much is known on the prevalence of intestinal spirochaetes in children. The aim of this study was to determine whether there is an association between pseudo-appendicitis and appendiceal spirochaetosis in children.

Methods

Archival appendix specimens from paediatric patients (less than 18 years old) were obtained from two Dutch hospitals (acute appendicitis, n = 63; pseudo-appendicitis, n = 55; control appendices, n = 33) and microscopically analysed by H&E staining and spirochaete-specific immunohistochemistry and Brachyspira species specific real-time PCR.

Results

Five out of 142 appendices were found to be positive, all in male patients: one in the acute appendicitis group, two in the pseudo-appendicitis group and two in the control group.

Conclusion

The results obtained do not provide evidence for a role of Brachyspira species infection in the aetiology of acute appendicitis in children.

Strains of the intestinal spirochaete Brachyspira pilosicoli attach to and aggregate erythrocytes

The anaerobic intestinal spirochaete Brachyspira pilosicoli colonizes the large intestine of various species of mammals and birds, where it may induce colitis. Strains of the spirochaete have also been isolated from the bloodstream of immunocompromised human patients and have been seen in liver sections, and a similar systemic spread was recently observed in experimentally infected chickens. Some other spirochaete species that may be present in blood attach to and aggregate erythrocytes, and this is believed to contribute to disease severity. The aim of the current study was to determine whether B. pilosicoli strains have the capacity to attach to and aggregate erythrocytes. Initially, four strains of B. pilosicoli were incubated with erythrocytes from sheep, cows, pigs, dogs, humans, chickens and geese, and were observed by phase-contrast microscopy. Only strain WesB attached, and this was only with erythrocytes from chickens and geese. Subsequently, six other strains of B. pilosicoli were tested just with goose erythrocytes, and five attached to and caused aggregation of the erythrocytes. Scanning and transmission electron microscopy demonstrated that spirochaetes abutted and apparently firmly attached to the erythrocyte membranes. Aggregation of erythrocytes by B. pilosicoli may contribute to disease severity in species that develop a spirochaetaemia.

SIGNIFICANCE AND IMPACT OF THE STUDY

The intestinal spirochaete Brachyspira pilosicoli has been isolated from the bloodstream of immunocompromised human patients, and spread to the liver has been reported in humans and in experimentally infected chickens. In this study, B. pilosicoli was shown to undergo attachment by one cell end to chicken and goose erythrocytes in vitro and to aggregate them. This activity has the potential to contribute to disease severity in avian and possibly other species that develop a spirochaetaemia and systemic spread. Avian erythrocytes may be useful for studying the mechanisms by which B. pilosicoli attaches to cells.

The pathogenic intestinal spirochaete Brachyspira pilosicoli forms a diverse recombinant species demonstrating some local clustering of related strains and potential for zoonotic spread

BACKGROUND

Brachyspira pilosicoli is an anaerobic spirochaete that can colonizes the large intestine of many host species. Infection is particularly problematic in pigs and adult poultry, causing colitis and diarrhea, but it is also known to result in clinical problems in human beings. Despite the economic importance of the spirochaete as an animal pathogen, and its potential as a zoonotic agent, it has not received extensive study.

METHODS

A multilocus sequence typing (MLST) method based on the scheme used for other Brachyspira species was applied to 131 B. pilosicoli isolates originating from different host species and geographical areas. A variety of phylogenetic trees were constructed and analyzed to help understand the data.

RESULTS

The isolates were highly diverse, with 127 sequence types and 123 amino acid types being identified. Large numbers (50-112) of alleles were present at each locus, with all loci being highly polymorphic. The results of Shimodaira-Hasegawa tests identified extensive genetic recombination, although the calculated standardized index of association value (0.1568; P <0.0005) suggested the existence of some clonality. Strains from different host species and geographical origins generally were widely distributed throughout the population, although in nine of the ten cases where small clusters of related isolates occurred these were from the same geographical areas or farms/communities, and from the same species of origin. An exception to the latter was a cluster of Australian isolates originating from pigs, chickens and a human being, suggesting the likelihood of relatively recent transmission of members of this clonal group between species.

CONCLUSIONS

The strongly recombinant population structure of B. pilosicoli contrasts to the more highly clonal population structures of the related species Brachyspira hyodysenteriae and Brachyspira intermedia, both of which are specialized enteric pathogens of pigs and poultry. The genomic plasticity of B. pilosicoli may help to explain why it has been able to adapt to colonize the large intestines of a wider range of hosts compared to other Brachyspira species. The identification of a clonal group of isolates that had been recovered from different host species, including a human being, suggests that zoonotic transmission by B. pilosicoli may occur in nature. Evidence for local transmission between the same host species also was obtained.

Brachyspira species and gastroenteritis in humans

Brachyspira species have been implicated as a potential cause of gastroenteritis in humans; this is, however, controversial. In 733 gastroenteritis cases and 464 controls, we found 29 samples positive for Brachyspira species (2.3% of cases and 2.6% of controls; P = 0.77). Brachyspira species were not associated with gastroenteritis in humans.

ENteric Immunity SImulator: a tool for in silico study of gastroenteric infections

Clinical symptoms of microbial infection of the gastrointestinal (GI) tract are often exacerbated by inflammation induced pathology. Identifying novel avenues for treating and preventing such pathologies is necessary and complicated by the complexity of interacting immune pathways in the gut, where effector and inflammatory immune cells are regulated by anti-inflammatory or regulatory cells. Here we present new advances in the development of the ENteric Immunity SImulator (ENISI), a simulator of GI immune mechanisms in response to resident commensal bacteria as well as invading pathogens and the effect on the development of intestinal lesions. ENISI is a tool for identifying potential treatment strategies that reduce inflammation-induced damage and, at the same time, ensure pathogen removal by allowing one to test plausibility of in vitro observed behavior as explanations for observations in vivo, propose behaviors not yet tested in vitro that could explain these tissue-level observations, and conduct low-cost, preliminary experiments of proposed interventions/treatments. An example of such application is shown in which we simulate dysentery resulting from Brachyispira hyodysenteriae infection and identify aspects of the host immune pathways that lead to continued inflammation-induced tissue damage even after pathogen elimination.

Comparative genomics of Brachyspira pilosicoli strains: genome rearrangements, reductions and correlation of genetic compliment with phenotypic diversity

Background

The anaerobic spirochaete Brachyspira pilosicoli causes enteric disease in avian, porcine and human hosts, amongst others. To date, the only available genome sequence of B. pilosicoli is that of strain 95/1000, a porcine isolate. In the first intra-species genome comparison within the Brachyspira genus, we report the whole genome sequence of B. pilosicoli B2904, an avian isolate, the incomplete genome sequence of B. pilosicoli WesB, a human isolate, and the comparisons with B. pilosicoli 95/1000. We also draw on incomplete genome sequences from three other Brachyspira species. Finally we report the first application of the high-throughput Biolog phenotype screening tool on the B. pilosicoli strains for detailed comparisons between genotype and phenotype.

Results

Feature and sequence genome comparisons revealed a high degree of similarity between the three B. pilosicoli strains, although the genomes of B2904 and WesB were larger than that of 95/1000 (~2,765, 2.890 and 2.596 Mb, respectively). Genome rearrangements were observed which correlated largely with the positions of mobile genetic elements. Through comparison of the B2904 and WesB genomes with the 95/1000 genome, features that we propose are non-essential due to their absence from 95/1000 include a peptidase, glycine reductase complex components and transposases. Novel bacteriophages were detected in the newly-sequenced genomes, which appeared to have involvement in intra- and inter-species horizontal gene transfer. Phenotypic differences predicted from genome analysis, such as the lack of genes for glucuronate catabolism in 95/1000, were confirmed by phenotyping.

Conclusions

The availability of multiple B. pilosicoli genome sequences has allowed us to demonstrate the substantial genomic variation that exists between these strains, and provides an insight into genetic events that are shaping the species. In addition, phenotype screening allowed determination of how genotypic differences translated to phenotype. Further application of such comparisons will improve understanding of the metabolic capabilities of Brachyspira species.

The physiological performance of a three-dimensional model that mimics the microenvironment of the small intestine

Our focus was to develop a three-dimensional (3D) human dynamic in vitro tissue model that mimics the natural microenvironment of the small intestine. We co-cultured human Caco-2 cells with primary-isolated human microvascular endothelial cells (hMECs) on decellularized porcine jejunal segments within a custom-made dynamic bioreactor system that resembles the apical and basolateral side of the intestine for up to 14 days. The obtained data were compared to results generated using routine static Caco-2 assays. We performed histology and immunohistochemistry. Permeability was measured using directed transport studies. Histological analyses revealed that in tissue-engineered segments, which had been cultured under dynamic conditions, the Caco-2 cells showed a high-prismatic morphology, resembling normal primary enterocytes within their native environment. We further identified that the transport of low permeable substances, such as fluorescein and desmopressin increased within the dynamic bioreactor cultures. Immunohistochemical staining showed a significantly higher expression of the efflux transport p-glycoprotein (p-gp) under dynamic culture conditions when compared to the static cultures. We conclude that the integration of physiological parameters is crucial for the establishment of a reliable 3D intestinal in vitro model, which enables the simulation of drug transport over the gut-blood-barrier in a simplified way.

Lactobacilli antagonize the growth, motility, and adherence of Brachyspira pilosicoli: a potential intervention against avian intestinal spirochetosis

Avian intestinal spirochetosis (AIS) results from the colonization of the ceca and colorectum of poultry by pathogenic Brachyspira species. The number of cases of AIS has increased since the 2006 European Union ban on the use of antibiotic growth promoters, which, together with emerging antimicrobial resistance in Brachyspira, has driven renewed interest in alternative intervention strategies. Probiotics have been reported as protecting livestock against infection with common enteric pathogens, and here we investigate which aspects of the biology of Brachyspira they antagonize in order to identify possible interventions against AIS. The cell-free supernatants (CFS) of two Lactobacillus strains, Lactobacillus reuteri LM1 and Lactobacillus salivarius LM2, suppressed the growth of Brachyspira pilosicoli B2904 in a pH-dependent manner. In in vitro adherence and invasion assays with HT29-16E three-dimensional (3D) cells and in a novel avian cecal in vitro organ culture (IVOC) model, the adherence and invasion of B. pilosicoli in epithelial cells were reduced significantly by the presence of lactobacilli (P < 0.001). In addition, live and heat-inactivated lactobacilli inhibited the motility of B. pilosicoli, and electron microscopic observations indicated that contact between the lactobacilli and Brachyspira was crucial in inhibiting both adherence and motility. These data suggest that motility is essential for B. pilosicoli to adhere to and invade the gut epithelium and that any interference of motility may be a useful tool for the development of control strategies.

Exposure to norepinephrine enhances Brachyspira pilosicoli growth, attraction to mucin and attachment to Caco-2 cells

Brachyspira pilosicoli is an anaerobic intestinal spirochaete that colonizes the large intestine of a variety of species of birds and mammals, including human beings. Colonization may result in a mild colitis and diarrhoea in a condition known as ‘intestinal spirochaetosis’. The catecholamine norepinephrine (NE), which is known to influence the behaviour of many bacterial species, may be present in the colon. The purpose of the current study was to determine whether exposure of B. pilosicoli to NE would influence its in vitro behaviour in assays that may reflect in vivo colonization potential. B. pilosicoli strain 95/1000 was used in all the assays. Addition of NE at a concentration of 0.05 mM to B. pilosicoli growing in anaerobic broth significantly increased spirochaete numbers after 4 days incubation. The effect of higher concentrations of NE was not significant. Exposure to 0.05 mM NE, but not to higher concentrations, also resulted in significantly more spirochaete cells entering capillary tubes containing 4 % porcine gastric mucin than occurred with untreated cultures. When NE was added to chemotaxis buffer in capillary tubes, significantly more spirochaetes were attracted to the buffer containing NE at 0.1, 0.5 and 1.0 mM than to buffer containing 0.05 mM NE, or when no NE was added. Exposure of B. pilosicoli cultures to 0.05 mM NE prior to incubation with Caco-2 monolayers resulted in more attachment to the monolayer than occurred with non-exposed cultures. These results show that at higher concentrations, NE acts as a chemoattractant for B. pilosicoli, and at 0.05 mM it increases the spirochaete's growth rate, attraction to mucin and rate of attachment to cultured enterocytes. These activities are likely to enhance the ability of B. pilosicoli to colonize, and may be induced by conditions that increase NE concentrations in the intestinal tract, such as the stresses associated with crowding.

The complete genome sequence of the pathogenic intestinal spirochete Brachyspira pilosicoli and comparison with other Brachyspira genomes

BACKGROUND

The anaerobic spirochete Brachyspira pilosicoli colonizes the large intestine of various species of birds and mammals, including humans. It causes "intestinal spirochetosis", a condition characterized by mild colitis, diarrhea and reduced growth. This study aimed to sequence and analyse the bacterial genome to investigate the genetic basis of its specialized ecology and virulence.

METHODOLOGY/PRINCIPAL FINDINGS

The genome of B. pilosicoli 95/1000 was sequenced, assembled and compared with that of the pathogenic Brachyspira hyodysenteriae and a near-complete sequence of Brachyspira murdochii. The B. pilosicoli genome was circular, composed of 2,586,443 bp with a 27.9 mol% G+C content, and encoded 2,338 genes. The three Brachyspira species shared 1,087 genes and showed evidence of extensive genome rearrangements. Despite minor differences in predicted protein functional groups, the species had many similar features including core metabolic pathways. Genes distinguishing B. pilosicoli from B. hyodysenteriae included those for a previously undescribed bacteriophage that may be useful for genetic manipulation, for a glycine reductase complex allowing use of glycine whilst protecting from oxidative stress, and for aconitase and related enzymes in the incomplete TCA cycle, allowing glutamate synthesis and function of the cycle during oxidative stress. B. pilosicoli had substantially fewer methyl-accepting chemotaxis genes than B. hyodysenteriae and hence these species are likely to have different chemotactic responses that may help to explain their different host range and colonization sites. B. pilosicoli lacked the gene for a new putative hemolysin identified in B. hyodysenteriae WA1. Both B. pilosicoli and B. murdochii lacked the rfbBADC gene cluster found on the B. hyodysenteriae plasmid, and hence were predicted to have different lipooligosaccharide structures. Overall, B. pilosicoli 95/1000 had a variety of genes potentially contributing to virulence.

CONCLUSIONS/SIGNIFICANCE

The availability of the complete genome sequence of B. pilosicoli 95/1000 will facilitate functional genomics studies aimed at elucidating host-pathogen interactions and virulence.