Identification of a 43-kDa outer membrane protein of Fusobacterium necrophorum that exhibits similarity with pore-forming proteins of other Fusobacterium species

The outer membrane protein of Fusobacterium necrophorum, 43K OMP, stimulates inflammatory cytokine production through nuclear factor kappa B activation

OBJECTIVE

Fusobacterium necrophorum causes bovine hepatic abscess, foot rot, mastitis, and endometritis. The 43 kDa outer membrane protein (43 K OMP) of F. necrophorum is a porin protein that plays an important role in infections by this bacterium, but the biological function and the pathogenesis of this protein are largely unknown.

METHODS

In this study, we investigated the role of the 43 K OMP in bacterial infection of bovine mammary epithelial cells (MAC-T cells) by Tandem Mass Tag proteomic analysis. The RAW264.7 cells were incubated with recombinant 43 K OMP (12.5 μg/mL) for 2 h, 4 h, 6 h, and 12 h, and then the inflammatory related protein and inflammatory cytokine production were measured by Western blot analysis and ELISA, the mRNA expression levels of inflammatory cytokine were measured by Real-Time PCR.

RESULTS

Proteomic analysis results demonstrated there were 224 differentially expressed proteins in the MAC-T cells stimulated with the 43 K OMP compared with control, and 118 proteins were upregulated and 106 proteins were downregulated. These differentially expressed proteins were mainly involved in NF-kappa B signaling, bacterial invasion of epithelial cells, cell adhesion, complement and coagulation cascades. The top six differentially expressed proteins were; MMP9, PLAU, STOM, PSMD13, PLAUR, and ITGAV, which were involved in a protein-protein interaction network. Furthermore, TLR/MyD88/NF-κB pathway related proteins and inflammatory cytokines (IL-6, TNF-α, and IL-1β) were assessed by Western blot analysis and ELISA. Results showed the 43 K OMP to enhance the expression of TLR4 protein at 2 h (P < 0.01) and the MyD88 protein at 4 h (P < 0.05) post-stimulation, and to decrease IκBα expression at 4 h, 6 h and 12 h (P < 0.05) post-infection, as well as induce phosphorylation at Ser536 (P < 0.01). Levels of IL-6, IL-1β, and TNF-α in the supernatants of mouse macrophages were increased (P < 0.05), as were mRNA expression levels of IL-6, IL-1β, and TNF-α (P < 0.05), while IL-4 mRNA expression was decreased (P < 0.05).

CONCLUSIONS

Taken together, these results suggested the important role for 43 K OMP in F. necrophorum infection, promoting the production of pro-inflammatory cytokines (IL-6 and TNF-α) by activation of the TLR/MyD88/NF-κB pathway. These findings provided a theoretical basis for a better understanding of the pathogenesis of F. necrophorum infection.

Evaluation of Immunoprotective Effects of Fusobacterium necrophorum Outer Membrane Proteins 43K OMP, Leukotoxin and Hemolysin Multi-Component Recombinant Subunit Vaccine in Mice

We evaluated the efficacy of three vaccine formulations containing different combinations of proteins (43K OMP, leukotoxin recombinant protein PL4 and hemolysin recombinant protein H2) and killed whole cell Fusobacterium necrophorum in preventing liver abscess. Four subcutaneous vaccines were formulated: vaccine 1 (43K OMP), vaccine 2 (PL4 and H2), vaccine 3 (43K OMP, PL4 and H2), and vaccine 4 (killed whole bacterial cell). 43K OMP, PL4, and H2 proteins were produced by using recombinant protein expression. To evaluate vaccine efficacy, we randomly allocated 50 BALB/c female mice to one of five different treatment groups: PBS control group, vaccine 1, vaccine 2, vaccine 3, and vaccine 4. Mice were vaccinated three times, with 14 days between each immunization. After immunization, the mice were challenged with F. necrophorum. The three key findings of this study are as follows: (1) Vaccine 3 has enabled mice to produce higher antibody titer following bacterial challenge, (2) in the liver pathology of mice, the vaccine 3 liver showed the least pathology, and (3) all four vaccines produced high levels of antibodies and cytokines in mice, but the level of vaccine 3 was the highest. Based on our results, it has been demonstrated that a mixture of F. necrophorum 43K OMP, PL4, and H2 proteins inoculated with mice can achieve protection against liver abscess in mice. Our research may therefore provide the basis for the development of a vaccine against F. necrophorum bovine infections.

Identification of Immunodominant Outer Membrane Proteins of Fusobacterium necrophorum from Severe Ovine Footrot By MALDI-TOF Mass Spectrometry

The aim of this study was to identify the immunodominant outer membrane proteins (OMPs) of Fusobacterium necrophorum from sheep affected with severe foot-rot. The OMP profile of ovine strains of F. necrophorum has not been well studied. We analyzed the OMP profile of the most frequent lktA variant JKS-F3 of F. necrophorum associated with severe ovine foot-rot with lesion score 4 in order to identify its major immunodominant OMPs. Electrophoretic separations of extracted OMPs showed a number of spots in two-dimensional electrophoretic gels. Two immunoreactive proteins of size around 43 kDa were identified through western blotting using hyperimmune sera raised in rabbits. These two immunogenic OMPs were analyzed by Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF/MS) which revealed that these two OMPs of lktA variant JKS-F3 of F. necrophorum showed 46 and 42 percent protein sequence coverage and scores of 125 and 114, respectively, with the reported 43 kDa outer membrane protein of F. necrophorum strain H05, a putative porin having properties similar to pore-forming proteins of anaerobic Gram-negative bacteria. These identified immunogenic OMPs will contribute to our understanding of the pathogenic role played by this organism in ovine foot-rot and could be exploited to devise an effective control strategy through development of an OMP-based recombinant vaccine to mitigate foot-rot in sheep and goats.

Screening of BHK-21 cellular proteins that interact with outer membrane protein 43K OMP of Fusobacterium necrophorum

Fusobacterium necrophorum is a Gram negative, spore-free, anaerobic bacterium that can cause pyogenic and necrotic infections in animals and humans. It is a major bovine pathogen and causes hepatic abscesses, foot rot, and necrotic laryngitis. The 43K OMP of F. necrophorum is an outer membrane protein with molecular weight of 43 kDa, exhibiting similarity to pore-forming proteins of other Fusobacterium species that plays an important role in bacterial infections. However, the role of 43K OMP in F. necrophorum adhesion remains unknown. In this study, we evaluated whether the 43K OMP of F. necrophorum mediates adhesion to BHK-21 cells and performed a preliminary screen of the proteins that interact with 43K OMP of F. necrophorum by immunoprecipitation-mass spectrometry. The results showed that the natural 43K OMP and recombinant 43K OMP could bind to BHK-21 cells, and preincubation of F. necrophorum with an antibody against the recombinant 43K OMP of F. necrophorum decreased binding to BHK-21 cells. Seventy differential interacting proteins were successfully screened by immunoprecipitation-mass spectrometry. Among these seventy differential interacting proteins, seven cell membrane proteins and four extracellular matrix proteins shown to be relevant to bacteria adhesion through subcellular localization and single-molecule function analysis. These data increase our understanding of the pathogenesis of F. necrophorum and provide a new theoretical basis for the design of antimicrobial drugs against F. necrophorum.

Phylogenetic and comparative genomics of the family Leptotrichiaceae and introduction of a novel fingerprinting MLVA for Streptobacillus moniliformis

Background

The Leptotrichiaceae are a family of fairly unnoticed bacteria containing both microbiota on mucous membranes as well as significant pathogens such as Streptobacillus moniliformis, the causative organism of streptobacillary rat bite fever. Comprehensive genomic studies in members of this family have so far not been carried out. We aimed to analyze 47 genomes from 20 different member species to illuminate phylogenetic aspects, as well as genomic and discriminatory properties.

Results

Our data provide a novel and reliable basis of support for previously established phylogeny from this group and give a deeper insight into characteristics of genome structure and gene functions. Full genome analyses revealed that most S. moniliformis strains under study form a heterogeneous population without any significant clustering. Analysis of infra-species variability for this highly pathogenic rat bite fever organism led to the detection of three specific variable number tandem analysis loci with high discriminatory power.

Conclusions

This highly useful and economical tool can be directly employed in clinical samples without laborious prior cultivation. Our and prospective case-specific data can now easily be compared by using a newly established MLVA database in order to gain a better insight into the epidemiology of this presumably under-reported zoonosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3206-0) contains supplementary material, which is available to authorized users.

Approved and novel strategies in diagnostics of rat bite fever and other Streptobacillus infections in humans and animals

Rat bite fever (RBF), a worldwide occurring and most likely under-diagnosed zoonosis caused by Streptobacillus moniliformis, represents the most prominent disease of Streptobacillus infections. Recently, novel members have been described, from which a reservoir in rats and other animal species and a zoonotic potential can be assumed. Despite regularly published case reports, diagnostics of RBF continues to represent a 'diagnostic dilemma', because the mostly applied 16S rRNA sequence analysis may be uncertain for proper pathogen identification. Virtually nothing is known regarding prevalence in humans and animal reservoirs. For a realistic assessment of the pathogen's spread, epidemiology and virulence traits, future studies should focus on the genomic background of Streptobacillus. Full genome sequence analyses of a representative collection of strains might facilitate to unequivocally identify and type isolates. Prevalence studies using selective enrichment mechanisms may also enable the isolation of novel strains and candidate species of this neglected group of microorganisms.

Phenotypic and Genotypic Characteristics of Members of the Genus Streptobacillus

The genus Streptobacillus (S.) remained monotypic for almost 90 years until two new species were recently described. The type species, S. moniliformis, is one of the two etiological agents of rat bite fever, an under-diagnosed, worldwide occurring zoonosis. In a polyphasic approach field isolates and reference strains of S. moniliformis, S. hongkongensis, S. felis as well as divergent isolates were characterized by comparison of molecular data (n = 29) and from the majority also by their physiological as well as proteomic properties (n = 22). Based on growth-independent physiological profiling using VITEK2-compact, API ZYM and the Micronaut system fastidious growth-related difficulties could be overcome and streptobacilli could definitively be typed despite generally few differences. While differing in their isolation sites and dates, S. moniliformis isolates were found to possess almost identical spectra in matrix-assisted laser desorption ionization-time of flight mass spectrometry and Fourier transform infrared spectroscopy. Spectroscopic methods facilitated differentiation of S. moniliformis, S. hongkongensis and S. felis as well as one divergent isolate. Sequencing of 16S rRNA gene as well as functional genes groEL, recA and gyrB revealed only little intraspecific variability, but generally proved suitable for interspecies discrimination between all three taxa and two groups of divergent isolates.