Brucella melitensis VirB12 recombinant protein is a potential marker for serodiagnosis of human brucellosis

Evaluation of twin-arginine translocation substrate proteins as potential antigen candidates for serodiagnosis of brucellosis

Introduction

Brucellosis, an infectious zoonotic disease caused by members of the genus Brucella, results in chronic multi-organ injury. Improving the specificity and sensitivity of serological methods for diagnosing brucellosis necessitates the development of novel diagnostic antigens. The twin-arginine translocation (Tat) pathway is responsible for transporting folded proteins across the cytoplasmic membrane and has been implicated in the virulence of Brucella. Three Tat substrate proteins-L,D-transpeptidase ErfK (A0577), linear amide C-N hydrolase YxeI (A1479), and thioesterase domain-containing protein EntF (B0249)-contribute significantly to Brucella virulence. However, the roles of these Tat substrate proteins in diagnosing brucellosis remain unclear.

Methods

In this study, ErfK, YxeI, and EntF were expressed in prokaryotic cells and utilized as diagnostic antigens. The clinical sera from bovines and sheep diagnosed with brucellosis were analyzed using indirect ELISA with these proteins.

Results

For bovine serum, the combined protein group (ErfK + YxeI + EntF) and YxeI demonstrated the highest diagnostic accuracy of 94.23% and 93.58%, respectively. Meanwhile, the combined protein group showed the strongest ability to detect Brucella in sheep serum, achieving an accuracy of 88.10%. Both the combined protein group and YxeI displayed no cross-reactivity with rabbit serum immunized against Yersinia enterocolitica O9, Escherichia coli O157:H7, Mycobacterium tuberculosis, Vibrio cholerae, Legionella, and Salmonella, indicating relatively good specificity.

Conclusion

The findings of this study suggest that Tat substrate proteins serve as promising candidate antigens with significant potential value for the clinical diagnosis of brucellosis.

Preparation and evaluation of Brucella T4SS recombinant proteins in serodiagnosis of human brucellosis based on TMT-based proteomics technology

Introduction

Brucellosis, a significant zoonotic infectious disease, poses a global health threat. Accurate and efficient diagnosis is crucial for prevention, control, and treatment of brucellosis. VirB proteins, components of the Type IV secretion system (T4SS) in Brucella, play a pivotal role in bacterial virulence and pathogenesis but have been understudied for their diagnostic potential.

Methods

Tandem Mass Tag (TMT) proteomics technology was utilized to identify highly expressed VirB proteins from wild-type Brucella strains. Recombinant T4SS proteins were prepared, and an indirect ELISA method was established for serological diagnosis of human brucellosis.

Results

Seven T4SS proteins (rVirB3, rVirB4, rVirB9, rBMEII0036, rVirB8, rVirB11, and rVirB10) were expressed used to construct the indirect ELISA method which showed high diagnostic accuracy. Sensitivity and specificity of the proteins exceeded 0.9100 and 0.9167, respectively, demonstrating good performance comparable to traditional LPS and Rose Bengal Ag antigens. Cross-reactivity was observed in a limited number of serum samples from febrile patients without brucellosis.

Conclusions

The study highlights the potential of VirB proteins as novel diagnostic antigens for human brucellosis. Future research can further optimize the use of VirB proteins in diagnostic assays and explore their applications in vaccine development.

Gated nanoprobe utilizing metal-organic frameworks for identifying and distinguishing between the wild strains and the vaccine strains of brucella

In the assay for Brucella, the identification and differentiation of wild strains and vaccine strains present a significant challenge. Currently, there aren't any commercially available product to address this issue. In this study, we have developed a novel gated nanoprobe by utilizing Metal-Organic Frameworks (MOFs) as a scaffold and hairpin DNA as a "gating switch". Specifically, Probe 1 with hairpin structure (P1h) targets a gene that is present in both wild strains Y3 (B. melitensis biovar 3) and vaccine strains A19 (Brucella abortus strains A19). We successfully applied this probe to screen positive samples of Brucella without any cross-reactivity with other substances. Additionally, we identified another specific gene exclusively found in wild strains, which serves as Probe 2 with hairpin structure (P2h) to confirm the strain type. Simultaneous detachment of both P1h and P2h from the MOFs leads to the release of Rhodamine 6G (Rho 6G) and Fluorescein (Flu), specifically indicating the presence of wild strains. If only P1h detaches and the Flu signal is detected, it suggests the presence of vaccine strains. Importantly, this method offers high accuracy, with a detection rate of 90% and a recovery rate of 94.71% to 107.65%, while avoiding cross-reactions with MO and TB. This one-step experiment provides reliable identification and differentiation of Y3 and A19, addressing concerns related to long periodicity, interference from individual variations, and the complex design of primers in existing laboratory methods. Furthermore, our approach successfully detects target 1 (T1) and target 2 (T2) at concentrations ranging from 10-6 M to 10-9 M, with a detection limit of 6.7 × 10-10 M and 6.4 × 10-10 M, respectively. Importantly, our strategy is cost-effective (around $1) and offers higher detection efficiency compared to traditional laboratory methods.

A designed peptide-based vaccine to combat Brucella melitensis, B. suis and B. abortus: Harnessing an epitope mapping and immunoinformatics approach

Vaccines against Brucella abortus, B. melitensis and B. suis have been based on weakened or killed bacteria, however there is no recombinant vaccine for disease prevention or therapy. This study attempted to predict IFN-γ epitopes, T cell cytotoxicity, and T lymphocytes in order to produce a multiepitope vaccine based on BtpA, Omp16, Omp28, virB10, Omp25, and Omp31 antigens against B. melitensis, B. abortus, and B. suis. AAY, GPGPG, and EAAAK peptides were used as epitope linkers, while the PADRE sequence was used as a Toll-like receptor 2 (TLR2) and TLR4 agonist. The final construct included 389 amino acids, and was a soluble protein with a molecular weight of 41.3 kDa, and nonallergenic and antigenic properties. Based on molecular docking studies, molecular dynamics simulations such as Gyration, RMSF, and RMSD, as well as tertiary structure validation methods, the modeled protein had a stable structure capable of interacting with TLR2/4. As a result, this novel vaccine may stimulate immune responses in B and T cells, and could prevent infection by B. suis, B. abortus, and B. melitensis.

The VirB System Plays a Crucial Role in Brucella Intracellular Infection

Brucellosis is a highly prevalent zoonotic disease caused by Brucella. Brucella spp. are gram-negative facultative intracellular parasitic bacteria. Its intracellular survival and replication depend on a functional virB system, an operon encoded by VirB1–VirB12. Type IV secretion system (T4SS) encoded by the virB operon is an important virulence factor of Brucella. It can subvert cellular pathway and induce host immune response by secreting effectors, which promotes Brucella replication in host cells and induce persistent infection. Therefore, this paper summarizes the function and significance of the VirB system, focusing on the structure of the VirB system where VirB T4SS mediates biogenesis of the endoplasmic reticulum (ER)-derived replicative Brucella-containing vacuole (rBCV), the effectors of T4SS and the cellular pathways it subverts, which will help better understand the pathogenic mechanism of Brucella and provide new ideas for clinical vaccine research and development.

Evaluation and Differential Diagnosis of a Genetic Marked Brucella Vaccine A19ΔvirB12 for Cattle

Brucella abortus is an important zoonotic pathogen that causes severe economic loss to husbandry and poses a threat to human health. The B. abortus A19 live vaccine has been extensively used to prevent bovine brucellosis in China. However, it is difficult to distinguish the serological response induced by A19 from that induced by natural infection. In this study, a novel genetically marked vaccine, A19ΔvirB12, was generated and evaluated. The results indicated that A19ΔvirB12 was able to provide effective protection against B. abortus 2308 (S2308) challenge in mice. Furthermore, the safety and protective efficacy of A19ΔvirB12 have been confirmed in natural host cattle. Additionally, the VirB12 protein allowed for serological differentiation between the S2308 challenge/natural infection and A19ΔvirB12 vaccination. However, previous studies have found that the accuracy of the serological detection based on VirB12 needs to be improved. Therefore, we attempted to identify potential supplementary antigens with differential diagnostic functions by combining label-free quantitative proteomics and protein chip technology. Twenty-six proteins identified only in S2308 were screened; among them, five proteins were considered as potential supplementary antigens. Thus, the accuracy of the differential diagnosis between A19ΔvirB12 immunization and field infection may be improved through multi-antigen detection. In addition, we explored the possible attenuation factors of Brucella vaccine strain. Nine virulence factors were downregulated in A19ΔvirB12. The downregulation pathways of A19ΔvirB12 were significantly enriched in quorum sensing, ATP-binding cassette transporter, and metabolism. Several proteins related to cell division were significantly downregulated, while some proteins involved in transcription were upregulated in S2308. In conclusion, our results contribute to the control and eradication of brucellosis and provide insights into the mechanisms underlying the attenuation of A19ΔvirB12.

Determination of investigation of the link between human and animal Brucella isolates in Iran using multiple-locus variable number tandem repeat method comprising 16 loci (MLVA-16)

Background

Epidemiological studies are important tools to assess the diversity of Brucella isolates and to estimate their epidemiological relationship among isolates from different geographical origins. In this study the MLVA16 (multiple-locus variable number tandem repeat analysis based on 16 loci) was employed to investigate the diversity of Brucella spp. Isolated from humans and animals for epidemiological purposes and to determine the most common Brucella genotypes in Iran.

Methods

We designed a molecular-based study to evaluate the potential reservoirs of human brucellosis. After isolation and identification of 54 Brucella spp human and animal specimens from three regions of Iran, bacterial genomic DNA was extracted MLVA with three panel was used for the genotyping of isolates. The size of PCR products were analyzed and converted to repeat unit numbers using a published allele numbering system and data set was imported into Bionumerics.

Results

Three isolates (5.55%) were identified as Brucella abortus and 51 (94.44%) as Brucella melitensis. Two isolates of Brucella abortus were from humans and one from an animal. Thirty-four Brucella melitensis isolates were from humans and 17 from animals. Using MLVA16-genotyping, 54 isolates with genetic similarity coefficient of 80% were divided into 46 genotypes and 22 genotypes were represented by a single isolate, while 4, 2, 1 and 2 genotypes were represented by 2, 3, 4 and 7 isolates, respectively. The most prevalent genotype was represented by 14 isolates. There were two other frequent genotypes each represented by seven isolates, among which only one was restricted to a geographic region. Discriminatory power for each locus was determined in this study and panel 2B shows the high discretionary power [Bruce04 (0.837), Bruce30 (0.806), Bruce 09 (0.787), Bruce 07 (0.772), Bruce16 (0.766)].

Conclusion

MLVA16 analysis of 54 Brucella isolates showed high level polymorphism in their genotypes. Only two genotypes, each observed in seven isolates, were related to one another and only one of these genotypes were found in to two separate regions.

Persister cells formation and expression of type II Toxin-Antitoxin system genes in Brucella melitensis (16M) and Brucella abortus (B19)

Background & Objective:

Persister cells are defined as a subpopulation of bacteria that are capable of reducing their metabolism and switching to dormancy in stress conditions. Persister cells formation has been attributed to numerous mechanisms, including stringent response and Toxin-Antitoxin (TA) systems. This study aimed to investigate the hypothetical role of TA systems in persister cells formation of Brucella strains by evaluating toxins of type II TA systems (RelE, Fic, BrnT, cogT) expression.

Methods:

Brucella strains treated with a lethal dose of gentamicin and ampicillin and to determine the number of surviving cells, bacterial colonies were counted at different time intervals. The role of TA systems in persister cell formation was then determined by toxin expression levels using qRT- PCR method.

Results:

Our results showed the viability of persister cells after 7 h. The results of relative qRT- PCR showed higher levels of toxin gene expression due to stress conditions, suggesting the possible role of TA systems in persister cells formation and antibiotics tolerance.

Conclusion:

The results of this study showed that considering the importance of persistence and the tolerance to antibiotics, further studies on persister cells formation and related genes such as the TA system genes in Brucella strains might help us to identify the precise mechanisms leading to persister cells formation.

Recombinant Omp2b antigen-based ELISA is an efficient tool for specific serodiagnosis of animal brucellosis

Control of brucellosis as a worldwide zoonotic disease is based on vaccination of animals and diagnosis of infected cases to be eradicated. Accurate and rapid detection of infected animals is of critical importance for preventing the spread of disease. Current detection of brucellosis is based on whole-cell antigens and investigating serum antibodies against Brucella lipopolysaccharide (LPS). The critical disadvantage is misdiagnosis of vaccinated animals as infected ones and also cross-reactions with other Gram-negative bacteria. Recombinant outer membrane protein 2b (Omp2b) of Brucella abortus was evaluated as a novel serodiagnostic target in comparison to conventional tests which are based on LPS. Recombinant Omp2b (rOmp2b) was expressed in Escherichia coli BL21 and purified by Ni²⁺-based chromatography. rOmp2b was evaluated in an indirect enzyme-linked immunosorbent assay (ELISA) system for diagnosis of brucellosis, with sera from Brucella-infected mice along with negative sera and sera from mice which were inoculated with other Gram-negative species for assurance of specificity. Thereafter, cattle sera collected from different regions were assessed along with known negative and known positive serum samples. We found that Omp2b can discriminate between Brucella-infected animals and non-infected ones. Results for assessment of two hundred and fifty cattle sera by Omp2b-based indirect ELISA which were compared to Rose Bengal plate agglutination test (RBPT) and serum tube agglutination test (SAT) showed that our proposed procedure has the sensitivity of 88.5%, specificity of 100%, and accuracy of 90.8%. We suggest that recombinant Omp2b could be used as a protein antigen for diagnosis of brucellosis in domestic animals and can be evaluated for detection of human brucellosis.

Immunogenic and protective antigens of Brucella as vaccine candidates

Brucella is an intracellular pathogen that causes abortion in domestic animals and undulant fever in humans. Due to the lack of a human vaccine against brucellosis, animal vaccines play an important role in the management of animal and human brucellosis for decades. Strain 19, RB51 and Rev1 are the approved Brucella spp. vaccine strains that are most commonly used to protect livestock against infection and abortion. However, due to some disadvantages of these vaccines, numerous studies have been conducted for the development of effective vaccines that could also be used in other susceptible animals. In this review, we compare different aspects of immunogenic antigens that have been a candidate for the brucellosis vaccine.

Molecular investigation of virulence factors of Brucella melitensis and Brucella abortus strains isolated from clinical and non-clinical samples

Brucella is zoonotic pathogen that induces abortion and sterility in domestic mammals and chronic infections in humans called Malta fever. It is a facultative intracellular potential pathogen with high infectivity. The virulence of Brucella is dependent upon its potential virulence factors such as enzymes and cell envelope associated virulence genes. The aim of this study was to investigate the Brucella virulence factors among strains isolated from humans and animals in different parts of Iran. Seventy eight strains of Brucella species isolated from suspected human and animal cases from several provinces of Iran during 2015-2016 and identified by phenotypic and molecular methods. The multiplex-PCR (M-PCR) assay was performed in order to detect the ure, wbkA, omp19, mviN, manA and perA genes by using gene specific primers. Out of 78 isolates of Brucella spp., 57 (73%) and 21 (27%) isolates were detected as B. melitensis and B. abortus, respectively, by molecular method. The relative frequency of virulence genes ure, wbkA, omp19, mviN, manA and perA were 74.4%, 89.7%, 93.6%, 94.9%, 100% and 92.3%, respectively. Our results indicate that the most of Brucella strains isolated from this region possess high percent of virulence factor genes (ure, wbkA, omp19, mviN, manA and perA) in their genome. So, each step of infection can be mediated by a number of virulence factors and each strain may have a unique combination of these factors that affected the rate of bacterial pathogenesis.

A Comparative Evaluation of ELISA, PCR, and Serum Agglutination Tests For Diagnosis of Brucella Using Human Serum

BACKGROUND & OBJECTIVE

Since the symptoms of Brucellosis are often atypical and nonspecific, using clinical signs alone to diagnose brucellosis is not advised; therefore, the diagnosis relies predominantly on laboratory testing. Currently, molecular, serological, and microbiological methods are used for diagnosis of this disease. In this study we examined ELISA, PCR and serum agglutination (SAT) methods on human patient serum samples.

METHODS

A total of 100 serum samples were collected from suspected patients. Fifty serum samples gave a positive result with the Wright test. The ELISA method was first employed on all samples for the detection of IgG and IgM antibodies against Brucella. Subsequently, the rapid PCR methodology was used to identify presence of Brucella genome in 500 µL of each serum sample. The B4/B5 primer pair was used for PCR‌ amplification.

RESULTS

Out of the 100 serum samples obtained from patients with suspected brucellosis, 50 samples tested positive by SAT and displayed high titers of 1/160. Of these 50 positive samples, 49 samples were positive as per the ELISA test whereas one sample tested negative. The PCR test was conducted on all 100 serum samples and results showed that the 45 serum samples that gave a positive agglutination test were also positive by PCR.

CONCLUSIONS

Various laboratory methods have been used or introduced for the detection of Brucella. Molecular methods such as PCR, a rapid and sensitive method for detection of bacteria, have also been reported. Based on the results of this study, we propose that the simultaneous use of serology and molecular techniques has the potential to overcome limitations of detection thereby enabling the selection of appropriate treatment for the patient.