Identification of an outer membrane protein of Fusobacterium necrophorum subsp. necrophorum that binds with high affinity to bovine endothelial cells

Identification of linear B cell epitopes on the leukotoxin protein of Fusobacterium necrophorum

OBJECTIVE

Fusobacterium necrophorum can casuse Lemierre's syndrome in humans and a range of illnesses, including foot rot and liver abscesses, in animals. The main virulence factor released by F. necrophorum is leukotoxin, which has been shown to have a strong correlation with the severity of the disease. Leukotoxin is commonly employed as the key antigen in the formulation of subunit vaccines. Therefore, identification of the B-cell epitope of F. necrophorum leukotoxin is necessary.

METHODS

In this research, we utilized lymphocyte hybridoma technology to develop a monoclonal antibody (mAb), 3D7, targeting the F. necrophorum leukotoxin protein. Identification of B-cell epitopes recognized by 3D7 mAb through Western blot, ELISA and dot blot using leukotoxin-truncated recombinant proteins and peptides, and through SWISS-MODEL homology modeling and PyMOL visualization.

RESULTS

The 3D7 mAb was identified as belonging to the IgG1 subclass with a κ-chain light chain. It demonstrated reactivity with the natural leukotoxin. The results showed that the 3D7 mAb recognizes a B-cell epitope of the F. necrophorum leukotoxin protein, I2168SSFGVGV2175 (EP-3D7). Sequence comparison analysis showed that EP-3D7 was highly conserved in F. necrophorum strains, but less conserved in other bacteria, indicating the specificity of EP-3D7. EP-3D7 is present on the surface of leukotoxin proteins in a β-folded manner.

CONCLUSIONS

In summary, these results establish EP-3D7 as a conserved antigenic epitope of F. necrophorum leukotoxin. It could be valuable in the development of vaccines and diagnostic reagents for F. necrophorum epitopes.

Characterization of Three New Outer Membrane Adhesion Proteins in Fusobacterium necrophorum

Fusobacterium necrophorum, an anaerobic Gram-negative pathogen, causes necrotic cattle infections, impacting livestock health and the US feedlot industry. Antibiotic administration is the mainstay for treating F. necrophorum infections, although resistance hampers their effectiveness. Vaccination, especially targeting outer membrane proteins (OMPs) due to their antigenic properties and host specificity, offers an alternative to antibiotics. This study identified high-binding-affinity adhesion proteins from F. necrophorum using binding and pull-down assays with bovine adrenal gland endothelial cells (EJG). Four OMP candidates (17.5 kDa/OmpH, 22.7 kDa/OmpA, 66.3 kDa/cell surface protein (CSP), and a previously characterized 43 kDa OMP) were expressed as recombinant proteins and purified. Rabbit polyclonal antibodies to recombinant OMPs were generated, and their ability to inhibit bacterial binding in vitro was assessed. The results show that treatment with individual polyclonal antibodies against 43 kDa significantly inhibited bacterial adhesion, while other antibodies were less potent. However, combinations of two or more antibodies showed a more prominent inhibitory effect on host-cell adhesion. Thus, our findings suggest that the identified OMPs are involved in fusobacterial attachment to host cells and may have the potential to be leveraged in combination for vaccine development. Future in vivo studies are needed to validate their roles and test the feasibility of an OMP-based subunit vaccine against fusobacterial infections.

Outer-Membrane Vesicles of Fusobacterium necrophorum: A Proteomic, Lipidomic, and Functional Characterization

Outer-membrane vesicles (OMVs) are extruded nanostructures shed by Gram-negative bacteria, containing periplasmic contents, and often including virulence factors with immunogenic properties. To assess their potential for use in vaccine development, we purified OMVs from the Fusobacterium necrophorum subspecies necrophorum, an opportunistic necrotic infection-causing pathogen, and characterized these structures using proteomics, lipid-profiling analyses, and cytotoxicity assays. A proteomic analysis of density-gradient-purified F. necrophorum OMVs identified 342 proteins, a large proportion of which were outer-membrane proteins (OMPs), followed by cytoplasmic proteins, based on a subcellular-localization-prediction analysis. The OMPs and toxins were among the proteins with the highest intensity identified, including the 43-kDa-OMP-, OmpA-, and OmpH-family proteins, the cell-surface protein, the FadA adhesin protein, the leukotoxin-LktA-family filamentous adhesin, the N-terminal domain of hemagglutinin, and the OMP transport protein and assembly factor. A Western blot analysis confirmed the presence of several OMPs and toxins in the F. necrophorum OMVs. The lipid-profiling analysis revealed phospholipids, sphingolipids, and acetylcarnitine as the main lipid contents of OMVs. The lactate-dehydrogenase-cytotoxicity assays showed that the OMVs had a high degree of cytotoxicity against a bovine B-lymphocyte cell line (BL-3 cells). Thus, our data suggest the need for further studies to evaluate the ability of OMVs to induce immune responses and assess their vaccine potential in vivo.

Case Report: Cerebrovascular Events Associated With Bacterial and SARS-CoV-2 Infections in an Adolescent

Neurologic manifestations associated with Covid-19 are increasingly reported, especially stroke and acute cerebrovascular events. Beyond cardiovascular risk factors associated with age, some young adults without medical or cardiovascular history had stroke as a presenting feature of Covid-19. Suggested stroke mechanisms in this setting are inflammatory storm, subsequent hypercoagulability, and vasculitis. To date, a handful of pediatric stroke cases associated with Covid-19 have been reported, either with a cardioembolic mechanism or a focal cerebral arteriopathy. We report the case of an adolescent who presented with febrile meningism and stupor. Clinical, biological, and radiological features favored the diagnosis of Lemierre syndrome (LS), with Fusobacterium necrophorum infection (sphenoid sinusitis and meningitis) and intracranial vasculitis. The patient had concurrent SARS-CoV-2 infection. Despite medical and surgical antimicrobial treatment, stroke prevention, and venous thrombosis prevention, he presented with severe cerebrovascular complications. Venous thrombosis and stroke were observed, with an extension of intracranial vasculitis, and lead to death. As both F. necrophorum and SARS-CoV-2 enhance inflammation, coagulation, and activate endothelial cells, we discuss how this coinfection may have potentiated and aggravated the usual course of LS. The potentiation by SARS-CoV-2 of vascular and thrombotic effects of a bacterial infection may represent an underreported cerebrovascular injury mechanism in Covid-19 patients. These findings emphasize the variety of mechanisms underlying stroke in this disease. Moreover, in the setting of SARS-CoV-2 pandemic, we discuss in what extent sanitary measures, namely, lockdown and fear to attend medical facilities, may have delayed diagnosis and influenced outcomes. This case also emphasizes the role of clinical assessment and the limits of telemedicine for acute neurological condition diagnosis.

Patients with Lemierre syndrome have a high risk of new thromboembolic complications, clinical sequelae and death: an analysis of 712 cases

BACKGROUND

Lemierre syndrome is characterized by head/neck vein thrombosis and septic embolism usually complicating an acute oropharyngeal bacterial infection in adolescents and young adults. We described the course of Lemierre syndrome in the contemporary era.

METHODS

In our individual-level analysis of 712 patients (2000-2017), we included cases described as Lemierre syndrome if these criteria were met: (i) primary site of bacterial infection in the head/neck; (ii) objectively confirmed local thrombotic complications or septic embolism. The study outcomes were new or recurrent venous thromboembolism or peripheral septic lesions, major bleeding, all-cause death and clinical sequelae.

RESULTS

The median age was 21 (Q1-Q3: 17-33) years, and 295 (41%) were female. At diagnosis, acute thrombosis of head/neck veins was detected in 597 (84%) patients, septic embolism in 582 (82%) and both in 468 (80%). After diagnosis and during in-hospital follow-up, new venous thromboembolism occurred in 34 (5.2%, 95% CI 3.8-7.2%) patients, new peripheral septic lesions became evident in 76 (11.7%; 9.4-14.3%). The rate of either was lower in patients who received anticoagulation (OR: 0.59; 0.36-0.94), higher in those with initial intracranial involvement (OR: 2.35; 1.45-3.80). Major bleeding occurred in 19 patients (2.9%; 1.9-4.5%), and 26 died (4.0%; 2.7-5.8%). Clinical sequelae were reported in 65 (10.4%, 8.2-13.0%) individuals, often consisting of cranial nerve palsy (n = 24) and orthopaedic limitations (n = 19).

CONCLUSIONS

Patients with Lemierre syndrome were characterized by a substantial risk of new thromboembolic complications and death. This risk was higher in the presence of initial intracranial involvement. One-tenth of survivors suffered major clinical sequelae.

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.

Draft Genome Sequences of Two Fusobacterium necrophorum Strains Isolated from the Uterus of Dairy Cows with Metritis

A commensal in the gastrointestinal tract, Fusobacterium necrophorum is involved in the pathogenicity of abscesses, foot rot, and metritis in cattle. Here, we present the draft genomes of two Fusobacterium necrophorum isolates from the uterus of dairy cows with metritis to allow for future comparative genome studies.

A commensal in the gastrointestinal tract, Fusobacterium necrophorum is involved in the pathogenicity of abscesses, foot rot, and metritis in cattle. Here, we present the draft genomes of two Fusobacterium necrophorum isolates from the uterus of dairy cows with metritis to allow for future comparative genome studies.

Characterization of Fusobacterium necrophorum subsp. necrophorum outer membrane proteins

Liver abscesses are of major economic importance to the cattle industry. These are mainly associated with the presence of Fusobacterium necrophorum, a non-spore forming and Gram-negative anaerobe. There are two main subspecies, F. necrophorum subspecies necrophorum and subsp. funduliforme, and they differ molecularly, morphologically, biochemically and in virulence. Previous studies have shown that the outer membrane proteins (OMP) of F. necrophorum subsp. necrophorum are important for its successful binding to immobilized bovine adrenal gland capillary endothelial (EJG) cells. In this study, a 42.4 kDa OMP of F. necrophorum subsp. necrophorum with the highest binding capacity to EJG cells was characterized. The gene was cloned into pFLAG-CTS vector and the proteins were subsequently expressed on the surface of E. coli BL21 DE3 cells. When E. coli carrying the recombinant plasmid (SM 2013) was induced using IPTG, there was significant enhancement in the binding to immobilized EJG cells compared to both uninduced SM 2013 and the E. coli carrying control vector only. When fixed EJG cells were incubated with purified native OMP, SM 2013 showed lowered levels of binding, compared to the uninduced SM 2013 and the E. coli carrying control vector only. Pre-incubation of induced SM 2013 with polyclonal antibodies made against the OMP reduced the binding to immobilized EJG cells to uninduced SM 2013 levels. This gain of function by recombinant E. coli confirms the ability of this protein to act as an adhesion to help binding of F. necrophorum subsp. necrophorum to host cells.

Evaluation of blood metabolites reflects presence or absence of liver abscesses in beef cattle

Liver abscesses constitute a prominent concern regarding animal health and profitability of the beef industry. Our objective was to evaluate potential biliary and blood indicators of liver abscesses. Twenty-nine beef bulls (initially averaging 356±70.5 kg and 253±30 days of age) were fed a high-concentrate diet during a performance test of 112 days, during which blood was collected at nine time points spaced 0.5-13 days apart within 56 days before slaughter. At the abattoir, blood and bile were collected and livers were inspected for liver abscesses. Results indicated that liver abscesses are associated with elevated levels of plasma cortisol and aspartate aminotransferase, and decreased levels of albumin, cholesterol and testosterone over the period before slaughter. Based on the blood samples collected during exsanguination, the presence of liver abscesses was associated with lower concentrations of thyroxine, albumin, cholesterol and alkaline phosphatase, and is suggested to be associated with lower blood carbon dioxide (P=0.08) and lower biliary cortisol metabolites (P=0.07). Albumin and cholesterol are established indicators of hepatic function and are consistently related to the presence of liver abscesses. Identifying blood parameters that predict liver abscesses has practical implications for cattle husbandry and for ensuring food safety.

Management of Reproductive Disease in Dairy Cows

Postpartum diseases are common in dairy cows, and their incidence contributes to reduced fertility and increased risk of culling, making their prevention and management extremely important. Reproductive efficiency has a major impact on economic success of any dairy production unit. Optimizing reproductive efficiency contributes to overall efficiency of production units, minimizing environmental impacts and contributing to sustainability of food production. Additionally, control of reproductive diseases is important for maintenance of health and welfare of dairy cows; for minimizing use of antibiotics; and ensuring a wholesome, safe, and nutritious product.

Interleukin-37 suppresses ICAM-1 expression in parallel with NF-κB down-regulation following TLR2 activation of human coronary artery endothelial cells

INTRODUCTION

The inflammatory receptor Toll-like receptors (TLRs) activation could induce endothelial inflammatory responses, which plays an important role in the development of many diseases including atherosclerosis. We already found that TLR2 activation of Peptidoglycan (PGN) stimulation could increase intercellular adhesion molecule-1 (ICAM-1) expression in HCAECs. Since anti-inflammatory cytokine interleukin (IL)-37 exhibits intra- and extracellular properties for suppressing innate inflammation, we want to investigate whether IL-37 suppresses ICAM-1 expression and this effect is in parallel with the inhibition of nuclear factor kappa B (NF-κB) activation upon PGN stimulation in HCAECs.

METHODS

HCAECs were treated with IL-37-transfection plasmid or silent mRNA or nothing for 24h, and we test IL-37 expression by immunoblotting. Same treatments prior to PGN stimulation (10μg/ml), we analyzed the expression of ICAM-1 and NF-κB mRNA at 0, 30min, 1 and 2h by real-time PCR. ICAM-1 protein at 24h and NF-κB activation at 0-2h were measured by immunoblotting.

RESULTS

IL-37 and silent IL-37 transfection change the expression of IL-37 protein. Stimulation of PGN increased both NF-κB activation and ICAM-1 expression at mRNA and protein level, but these inflammatory cytokines' expression was significantly decreased in IL-37-transfection cells. Interestingly, both NF-κB activation and ICAM-1 expression were significantly increased when IL-37 was silent.

CONCLUSIONS

As an anti-inflammatory cytokine, IL-37 could decrease both NF-κB and ICAM-1 expression upon TLR2 activation in HCAECs. The suppressed effect of IL-37 on ICAM-1 may be due to its inhibition on NF-κB.