Aggregatibacter actinomycetemcomitans as the Aetiological Cause of Rheumatoid Arthritis: What Are the Unsolved Puzzles?

Leukotoxin A (LtxA) is the major virulence factor of an oral bacterium known as Aggregatibacter actinomycetemcomitans (Aa). LtxA is associated with elevated levels of anti-citrullinated protein antibodies (ACPA) in rheumatoid arthritis (RA) patients. LtxA targets leukocytes and triggers an influx of extracellular calcium into cytosol. The current proposed model of LtxA-mediated hypercitrullination involves the dysregulated activation of peptidylarginine deiminase (PAD) enzymes to citrullinate proteins, the release of hypercitrullinated proteins through cell death, and the production of autoantigens recognized by ACPA. Although model-based evidence is yet to be established, its interaction with the host’s immune system sparked interest in the role of LtxA in RA. The first part of this review summarizes the current knowledge of Aa and LtxA. The next part highlights the findings of previous studies on the association of Aa or LtxA with RA aetiology. Finally, we discuss the unresolved aspects of the proposed link between LtxA of Aa and RA.

CT-Guided Biopsy in Suspected Spondylodiscitis--The Association of Paravertebral Inflammation with Microbial Pathogen Detection

Objectives

To search for imaging characteristics distinguishing patients with successful from those with futile microbiological pathogen detection by CT-guided biopsy in suspected spondylodiscitis.

Methods

34 consecutive patients with suspected spondylodiscitis underwent CT-guided biopsy for pathogen detection. MR-images were assessed for inflammatory infiltration of disks, adjacent vertebrae, epidural and paravertebral space. CT-images were reviewed for arrosion of adjacent end plates and reduced disk height. Biopsy samples were sent for microbiological examination in 34/34 patients, and for additional histological analysis in 28/34 patients.

Results

Paravertebral infiltration was present in all 10/10 patients with positive microbiology and occurred in only 12/24 patients with negative microbiology, resulting in a sensitivity of 100% and a specificity of 50% for pathogen detection. Despite its limited sensitivities, epidural infiltration and paravertebral abscesses showed considerably higher specificities of 83.3% and 90.9%, respectively. Paravertebral infiltration was more extensive in patients with positive as compared to negative microbiology (p = 0.002). Even though sensitivities for pathogen detection were also high in case of vertebral and disk infiltration, or end plate arrosion, specificities remained below 10%.

Conclusions

Inflammatory infiltration of the paravertebral space indicated successful pathogen detection by CT-guided biopsy. Specificity was increased by the additional occurrence of epidural infiltration or paravertebral abscesses.

Human Wound Infection with Mannheimia glucosida following Lamb Bite

Mannheimia spp. are veterinary pathogens that can cause mastitis and pneumonia in domestic cattle and sheep. While Mannheimia glucosida can be found as normal flora in oral and respiratory mucosa in sheep, there have been no reported cases of human infection with this organism.

[Severe purulent and necrotizing glossitis in a fallow deer (Dama dama) due to an infection with the involvement of Mannheimia granulomatis]

Post mortem examination of a young fallow deer (Dama dama) revealed a severe purulent and necrotizing glossitis as well as a multifocal necrotizing and ulcerative rumenitis and typhlitis. The animal was cachectic. Mannheimia (M.) sp. was isolated from the tongue lesions and identified as M. granulomatis by MALDI-TOF MS and 16S rRNA sequencing. Mycosis and BVDV infection were excluded. Few publications are dealing with similar macroscopic findings associated with the isolation of M. granulomatis in cattle and roe deer. Therefore, M. granulomatis should also be taken into consideration when such lesions occur in other ruminants. Based on our findings in case of gross pathological lesions of the tongue of ruminants a Mannheimia granulomatis-infection should be investigated as well as the possible role of Fusobacterium necrophorum, Actinobacillus lignieresii or Actinomyces bovis.

Mannheimia haemolytica vegetative endocarditis in a Suffolk wether

A 12-week-old Suffolk wether was diagnosed with bacterial endocarditis associated with Mannheimia haemolytica. The wether had shown signs of lethargy, inappetance, fever, and a grade 5 of 6 holosystolic murmur. Mannheimia haemolytica was cultured from blood premortem and the valvular lesion postmortem.

NLRP3 inflammasome is required for apoptosis of Aggregatibacter actinomycetemcomitans-infected human osteoblastic MG63 cells

Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is a Gram-negative bacterium which is implicated in the pathogenesis of human periodontal disease and in particular aggressive periodontitis. Virulence factors from A. actinomycetemcomitans have been shown to induce apoptosis of osteoblasts, however, the underlying mechanisms of the induction of apoptosis are poorly understood. In the present study, the infection of A. actinomycetemcomitans in human osteoblastic MG63 cells was established. Accordingly, A. actinomycetemcomitans infection enhanced significant apoptosis of MG63 cells. We found that both expression levels of NLRP3 and ASC were increased dramatically after MG63 cell cultures exposed to A. actinomycetemcomitans. Moreover, the secretion of mature interleukin-1β (IL-1β) and IL-18 were extensively induced in A. actinomycetemcomitans-infected cells as compared with non-invasion group of MG63 cell cultures, indicating the activation of the NLRP3 inflammasome during infection. Finally, we found that the knockdown expression of NLRP3 by specific small interfering RNA (siRNA) attenuated apoptosis of A. actinomycetemcomitans-infected MG63 cells. Our data suggest that A. actinomycetemcomitans promotes apoptosis of human osteoblasts at least partially through the NLRP3 inflammasome.

A comparison of Aggregatibacter actinomycetemcomitans (Aa) virulence traits in a rat model for periodontal disease

Our aim was to explore the effects of Cytolethal Distending toxin (Cdt) in a well established rat model of periodontal disease where leukotoxin (LtxA) was thought to have no known effect. In vitro studies, were used to assess CdtB activity using Aa Leukotoxin as a negative control. These studies showed that both CdtB and LtxA (unexpectedly) exerted significant effects on CD4⁺ T cells. As a result we decided to compare the effects of these two prominent Aa virulence factors on bone loss using our rat model of Aa-induced periodontitis. In this model, Aa strains, mutant in cdtB and ltxA, were compared to their parent non-mutant strains and evaluated for colonization, antibody response to Aa, bone loss and disease. We found that bone loss/disease caused by the ltxA mutant strain, in which cdtB was expressed, was significantly less (p<0.05) than that due to the wild type strain. On the other hand, the disease caused by cdtB mutant strain, in which ltxA was expressed, was not significantly different from the wild type strain. This data indicates that Aa LtxA exerts a greater effect on bone loss than Cdt in this rat model of periodontal disease and supports the utility of this model to dissect specific virulence factors as they relate to immunopathology in studies of Aa-induced disease.

Bovine respiratory syncytial virus and Histophilus somni interaction at the alveolar barrier

Our previous studies showed that Histophilus somni and bovine respiratory syncytial virus (BRSV) act synergistically in vivo to cause more severe bovine respiratory disease than either agent alone causes. Since H. somni surface and secreted immunoglobulin binding protein A (IbpA) causes retraction of bovine alveolar type 2 (BAT2) cells and invasion between BAT2 cells in vitro, we investigated mechanisms of BRSV-plus-H. somni infection at the alveolar barrier. BRSV treatment of BAT2 cells prior to treatment with IbpA-rich H. somni concentrated culture supernatant (CCS) resulted in increased BAT2 cell rounding and retraction compared to those with either treatment alone. This mimicked the increased alveolar cell thickening in calves experimentally infected with BRSV followed by H. somni compared to that in calves infected with BRSV or H. somni alone. BRSV-plus-H. somni CCS treatment of BAT2 cells also enhanced paracellular migration. The effect of matrix metalloproteinases (MMPs) was investigated as well because microarray analysis revealed that treatment with BRSV plus H. somni synergistically upregulated BAT2 cell expression of mmp1 and mmp3 compared to that in cells treated with either agent alone. Enzyme-linked immunosorbent assay (ELISA) confirmed that MMP1 and MMP3 protein levels were similarly upregulated. In collagen I and collagen IV (targets for MMP1 and MMP3, respectively) substrate zymography, digestion was increased with supernatants from dually treated BAT2 cells compared with those from singly treated cells. Enhanced breakdown of collagen IV in the basal lamina and of fibrillar collagen I in the adjacent interstitium in the dual infection may facilitate dissemination of H. somni infection.

Cytolethal distending toxin in isolates of Aggregatibacter actinomycetemcomitans from Ghanaian adolescents and association with serotype and disease progression

BACKGROUND AND OBJECTIVES

The cytolethal distending toxin (Cdt) is a highly conserved exotoxin that are produced by a number of Gram negative bacteria, including Aggregatibacter actinomycetemcomitans, and affects mammalian cells by inhibiting cell division and causing apoptosis. A complete cdt-operon is present in the majority of A. actinomycetemcomitans, but the proportion of isolates that lack cdt-encoding genes (A, B and C) varies according to the population studied. The objectives of this study were to examine serotype, Cdt-genotype, and Cdt-activity in isolates of A. actinomycetemcomitans collected from an adolescent West African population and to examine the association between the carrier status of A. actinomycetemcomitans and the progression of attachment loss (AL).

MATERIALS AND METHODS

A total of 249 A. actinomycetemcomitans isolates from 200 Ghanaian adolescents were examined for serotype and cdt-genotype by PCR. The activity of the Cdt-toxin was examined by DNA-staining of exposed cultured cells and documented with flow cytometry. The periodontal status of the participants was examined at baseline and at a two-year follow-up.

RESULTS

Presence of all three cdt-encoding genes was detected in 79% of the examined A. actinomycetemcomitans isolates. All these isolates showed a substantial Cdt-activity. The two different cdt-genotypes (with and without presence of all three cdt-encoding genes) showed a serotype-dependent distribution pattern. Presence of A. actinomycetemcomitans was significantly associated with progression of AL (OR = 5.126; 95% CI = [2.994-8.779], p<0.001).

CONCLUSION

A. actinomycetemcomitans isolated from the Ghanaian adolescents showed a distribution of serotype and cdt-genotype in line with results based on other previously studied populations. Presence of A. actinomycetemcomitans was significantly associated with disease progression, in particular the b serotype, whereas the association with disease progression was not particularly related to cdt-genotype, and Cdt-activity.

Identification of a novel Mannheimia granulomatis lineage from lesions in roe deer (Capreolus capreolus)

Eight atypical Mannheimia isolates were isolated from lesions in roe deer (Capreolus capreolus). Traditional classification based on morphologic and physiologic traits showed that they belong to a distinct biogroup (taxon) within genus Mannheimia. Extensive phenotypic characterization suggested that the isolates should be classified as M. granulomatis, although the presence of distinct traits justified their classification into a separate biogroup within this species. Phylogenetic analyses based on 16S rRNA sequences from two roe deer isolates and 41 other Mannheimia strains supported that the roe deer isolates form a monophyletic group within M. granulomatis. The lktA genotype was present in all roe deer isolates based on Southern blot analysis, whereas the corresponding beta-hemolytic phenotype was absent in one of these isolates.

Molecular and ultrastructural studies of the fibrotic lesions of bovine focal proliferative fibrogranulomatous panniculitis (Lechiguana)

This work aimed to investigate some aspects related to the pathogenicity of Lechiguana, a bovine fibroproliferative lesion characterized by rapid collagen accumulation. Light and transmission electron microscopy and in situ hybridization studies were performed in order to elucidate the fibrogenic activity of this lesion. The characterization of fibroblastic plasticity in the lesion was done by immunohistochemical study for alpha-smooth-muscle cell actin. The ovoid-shaped cells presented positive reaction for alpha-smooth-muscle cell actin in their cytoplasm and, at the electron-microscopic level demonstrated basal lamina-like material adjacent to the external surface and collagen fibrils that corresponded to a cell population phenotypically similar to the myofibroblast. We also investigated alpha1 collagen type I mRNA at different times of evolution of Lechiguana lesions, using isotopic and non-isotopic in situ hybridization. The results strongly suggest the involvement of a myofibroblast-like cell population that expresses mRNA for type I collagen and is probably associated with the increase of collagen deposition.

In vivo studies of Gallibacterium anatis infection in chickens

The aim of the present study was to investigate the pathology in normal or immunosuppressed chickens followed intravenous or intraperitoneal inoculation with a well-characterized strain of Gallibacterium anatis. Two groups of 30 15-week-old commercial brown laying chickens were used, having been screened and found negative for Gallibacterium organisms. One group was treated with 5-fluorouracil to promote heterophil depletion, while the other was saline treated. Ten days later 15 chickens from each group were inoculated either intravenously or intraperitoneally with 3.3 x 10(7) colony-forming units of G. anatis strain 12656-12. Subsets of chickens were sacrificed at 3, 12 or 24 h post-infection and examined for lesions. Livers and spleens were examined by culture and by fluorescent in situ hybridization. Intravenously infected birds showed severe septicaemic lesions in both the normal and immunosuppressed birds. Mortality was recorded only in the latter, with an overall rate of 73%. The intraperitoneally infected chickens of normal immune status showed various degrees of localized purulent peritonitis at the inoculation site, but in the immunosuppressed birds the entire peritoneum tended to be involved along with the abdominal organs. This was similar to previous descriptions of natural infections and may represent a useful infection model for detailed analysis of Gallibacterium virulence factors and pathogenesis.

Detection of Gallibacterium spp. in chickens by fluorescent 16S rRNA in situ hybridization

Gallibacterium has recently been included as a new genus of the family Pasteurellaceae Pohl 1981, which encompasses bacteria previously reported as Pasteurella anatis, "Actinobacillus salpingitidis," and avian Pasteurella haemolytica-like organisms. So far, identification has exclusively relied on phenotypic characterization. We present a method based on a cyanine dye 3.18-labeled in situ hybridization probe targeting 16S rRNA to allow specific detection of bacteria belonging to the genus Gallibacterium. The probe, GAN850, showed no cross-reactivity to 25 other poultry-associated bacterial species, including members of the families Pasteurellaceae, Enterobacteriaceae, and Flavobacteriaceae, when cross-reactivities were evaluated by whole-cell hybridization. The probe was further evaluated by hybridization to formalin-fixed spleen and liver tissues from experimentally infected chickens, in which it proved to be useful for the detection of Gallibacterium. Additionally, determination of the spatial distribution and the host cell affiliation of Gallibacterium at various times during the infection process was possible. In conclusion, the in situ hybridization technique described may be of use as a diagnostic tool as well as for studies to elucidate the pathogenesis of Gallibacterium infections in chickens.

Depletion of pulmonary intravascular macrophages inhibits acute lung inflammation

Pulmonary intravascular macrophages (PIMs) are present in ruminants and horses. These species are highly sensitive to acute lung inflammation compared with non-PIM-containing species such as rats and humans. There is evidence that rats and humans may also recruit PIMs under certain conditions. We investigated precise contributions of PIMs to acute lung inflammation in a calf model. First, PIMs were recognized with a combination of in vivo phagocytic tracer Monastral blue and postembedding immunohistology with anti-CD68 monoclonal antibody. Second, gadolinium chloride depleted PIMs within 48 h of treatment (P < 0.05). Finally, PIMs contain TNF-alpha, and their depletion reduces cells positive for IL-8 (P < 0.05) and TNF-alpha (P < 0.05) and histopathological signs of acute lung inflammation in calves infected with Mannheimia hemolytica. The majority of IL-8-positive inflammatory cells in lung septa of infected calves were platelets. Platelets from normal cattle contained preformed IL-8 that was released upon in vitro exposure to thrombin (P < 0.05). These novel data show that PIMs, as the source of TNF-alpha, promote recruitment of inflammatory cells including IL-8-containing platelets to stimulate acute inflammation and pathology in lungs. These data may also be relevant to humans due to our ability to recruit PIMs.

A selectin inhibitor decreases neutrophil infiltration during acute Mannheimia haemolytica pneumonia

The degree to which the selectin inhibitor TBC1269 reduces neutrophil infiltration in specific microscopic locations of the lung during acute pneumonia of neonates was determined. Neonatal calves were inoculated intrabronchially with Mannheimia (Pasteurella) haemolytica or saline, and lung tissue was collected at 2 and 6 hours postinoculation (PI). One 6-hour group inoculated with M. haemolytica received TBC1269 intravenously before and after inoculation with M. haemolytica. Infiltrates of neutrophils were significantly higher in the alveolar lumen and septae but lower in the bronchial lumen and epithelium at 6 hours PI than at 2 hours PI. Significantly fewer neutrophils (P < 0.05) were present in the alveolar lumen and septae, and the bronchiolar lumen and lamina propria in the lungs of TBC1269-treated calves compared with untreated calves at 6 hours PI. TBC1269 did not alter the infiltration into bronchi and blood vessels or the expression of the selectin-independent adhesion molecule, ICAM-1. This work suggests that during acute pneumonia of neonates 1) neutrophil infiltrates progressively increase in the alveolar lumens and septae but decrease in the bronchial lumen and epithelium with time, 2) TBC1269 reduces neutrophil infiltration into specific regions of alveoli and bronchioles rather than uniformly throughout the lung, and 3) selectin inhibition does not affect the location and intensity of ICAM-1 expression.

Taxon 20 (Fam. Pasteurellaceae) infections in European brown hares (Lepus europaeus)

Hemolytic bacteria, phenotypically related to organisms previously identified as Pasteurella haemolytica and tentatively named Taxon 20, were isolated from cases of purulent bronchopneumonia and from conjunctivitis in European brown hares (Lepus europaeus). The bronchopneumonia, sometimes accompanied by lesions in other organs, occurred without other concomitant disease. The conjunctivitis was found mainly in animals suffering from the European brown hare syndrome.