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Iron is an essential element required for all organisms. Iron response regulator (Irr) is a crucial transcriptional regulator and can affect the growth and iron uptake of Brucella. The growth rate of Brucella melitensis M5-90 irr mutant was significantly lower than that of B. melitensis M5-90 under normal or iron-sufficient conditions, however, the growth rate of the B. melitensis M5-90 irr mutant was significantly higher than that of B. melitensis M5-90 under iron-limited conditions. In addition, irr mutation significantly reduced iron uptake under iron-limited conditions. Previous studies suggested that the Irr protein has multiple target genes in the Brucella genome that are involved in iron metabolism. Therefore, in the present study, a Dap-seq approach was used to investigate the other iron metabolism genes that are also regulated by the Irr protein in Brucella. A total of seven genes were identified as target genes for Irr in this study and the expression levels of these seven genes were similar in both the RNA-seq and qRT-PCR results. The electrophoretic mobility shift assay confirmed that six out of the seven genes, namely rirA (BME_RS13665), membrane protein (BME_RS01725), hypothetical protein (BME_RS09560), ftrA (BME_RS14525), cation-transporting P-type ATPase (zntA) (BME_RS10660), and 2Fe-2S binding protein (BME_RS13655), interact with the Irr protein. Furthermore, the iron utilization and growth assay experiments confirmed that rirA was involve in iron metabolism and growth of Brucella. In summary, our results identified six genes regulated by the Irr protein that may participate in iron metabolism, and the rirA was identified as a regulon of Irr and it also plays a role in iron metabolism of Brucella. Collectively, these results provide valuable insights for the exploration of Brucella iron metabolism. Author summary: Iron response regulator (Irr) plays a key role in iron metabolism of Brucella. In this study, the Brucella melitensis M5-90 irr mutant appeared significant different of growth and iron utilization rate compared with that of the Brucella melitensis M5-90 strain. However, the specific binding sites of Irr in Brucella are not fully understood. Here, we used Dap-seq to identify the potential target genes of Irr in the genome of Brucella melitensis M5-90. A total of seven genes were identified as target genes for Irr and the expression of levels of these seven genes were identified using qRT-PCR. In addition, Six out of seven genes namely rirA, membrane protein, hypothetical protein, ftrA, zntA and 2Fe-2S binding protein interact with the Irr protein. Furthermore, the mutation of rirA markedly affected the iron utilization and growth rate of Brucella. Overall, these results provide valuable insights for the exploration of Brucella iron metabolism. [ABSTRACT FROM AUTHOR]

Exosomes, membrane vesicles released extracellularly from cells, contain nucleic acids, proteins, lipids and other components, allowing the transfer of material information between cells. Recent studies reported the role of exosomes in pathogenic microbial infection and host immune mechanisms. Brucella‐invasive bodies can survive in host cells for a long time and cause chronic infection, which causes tissue damage. Whether exosomes are involved in host anti‐Brucella congenital immune responses has not been reported. Here, we extracted and identified exosomes secreted by Brucella melitensis M5 (Exo‐M5)‐infected macrophages, and performed in vivo and in vitro studies to examine the effects of exosomes carrying antigen on the polarization of macrophages and immune activation. Exo‐M5 promoted the polarization of M1 macrophages, which induced the significant secretion of M1 cytokines (tumour necrosis factor‐α and interferon‐γ) through NF‐κB signalling pathways and inhibited the secretion of M2 cytokines (IL‐10), thereby inhibiting the intracellular survival of Brucella. Exo‐M5 activated innate immunity and promoted the release of IgG2a antibodies that protected mice from Brucella infection and reduced the parasitaemia of Brucella in the spleen. Furthermore, Exo‐M5 contained Brucella antigen components, including Omp31 and OmpA. These results demonstrated that exosomes have an important role in immune responses against Brucella, which might help elucidate the mechanisms of host immunity against Brucella infection and aid the search for Brucella biomarkers and the development of new vaccine candidates. [ABSTRACT FROM AUTHOR]

Background: This case report describes the clinical process of a shepherd who suffered brucellosis-related endocarditis (BE) and spondylitis (BS) and was infected with Brucella melitensis biovar 3 (B. melitensis biovar 3).Case Presentation: A 55-year-old male patient was admitted to The First Affiliated Hospital of Shihezi University on October 11, 2018, due to over 3 months of intermittent fever, back pain, and heart trouble. The Rose Bengal Plate test was positive, the standard agglutination test titer for brucellosis was 1/800, and the blood culture was positive for B. melitensis biovar 3. Three instances of transthoracic echocardiography examination at days 1, 25, and 376 after admission to the hospital and magnetic resonance imaging (MRI) and computed tomography (CT) checks at days 5 and 38 revealed that the size of the vegetation on the posterior leaflet of the mitral valve increased from 0.7 × 1.4 cm to 1.2 × 1.5 cm and that the left atrium and ventricle were enlarged. The MRI and CT results showed hyperplasia of the second and third vertebra, a cold abscess formed on both sides of the psoas major muscles, and the vertebra hyperplasia became aggravated at a later time point. The patient's situation deteriorated, and heart failure was discovered on October 22, 2019. At the moment of submission of this manuscript, the patient remains in bed at home because of severe debility caused by brucellosis.Conclusions: This is the first reported case of endocarditis combined with spondylitis caused by B. melitensis biovar 3 in a shepherd. Brucellosis infection can cause work-power losses because of misdiagnosis or a lack of proper treatment. Early diagnosis and treatment are essential for a successful outcome. [ABSTRACT FROM AUTHOR]

• A multi-epitope subunit vaccine (MEVocb) was developed using a reverse vaccinology approach to prevent Brucella infection. • The MEVocb showed high immunogenicity and elicited a specific humoral and cellular immune response in mice. • The MEVocb has strong antibody response and immune protection. • The MEVocb provided statistically significant protection against Brucella melitensis 043 in Xinjiang. • The MEVocb construct demonstrates the potential for an acceptable new Brucella subunit vaccine. Brucellosis, a zoonosis caused by Brucella , is highly detrimental to both humans and animals. Most existing vaccines are live attenuated vaccines with safety flaws for people and animals. Therefore, it is advantageous to design a multi-epitope subunit vaccine (MEV) to prevent Brucella infection. To this end, we applied a reverse vaccinology approach. Six cytotoxic T cell (CTL) epitopes, seven T helper cell (HTL) epitopes, and four linear B cell epitopes from CU/ZN-SOD, Omp31, and BP26 were obtained. We linked the CTL, HTL, B-cell epitopes, the appropriate CTB molecular adjuvant, and the universal T helper lymphocyte epitope, PADRE, with linkers AAY, GPPGG, and KK, respectively. This yielded a 412-amino acid MEV construct, which we named MEVcob. The immunogenicity, stability, safety, and feasibility of the construct were evaluated by bioinformatics tools (including the AlphaFold2 prediction tool, the AlphaFold2 tool, NetMHC-I pan 4.0 server, IEDB MHC-I server, ABCpred service, and C-ImmSim server); the physicochemical properties, secondary and tertiary structures, and binding ability of MEVocb to toll-like receptor 4 (TLR4) was analyzed. Then, codon adaptation and computer cloning studies were performed. MEVocb is highly immunogenic in immunostimulation experiments, The proteins translated by these sequences were relatively stable, exhibiting a high antigenic index. Furthermore, mouse experiments confirmed that the MEVocb construct could raise IFN-γ, IgG, IgG2a, IgG1, IL-2, TNF-α levels in mice, indicating that induced a specific humoral and cellular immune response in BALB/c mice. This vaccine induced a statistically significant level of protection in BALB/c mice when challenged with Brucella melitensis 043 in Xinjiang. Briefly, we utilized immunoinformatic tools to design a novel multi-epitope subunit candidate vaccine against Brucella. This vaccine aims to induce host immune responses and confer specific protective effects. The study results offer a theoretical foundation for the development of a novel Brucella subunit vaccine. [ABSTRACT FROM AUTHOR]

Abstract Brucellosis is an infectious disease that brings enormous economic burdens for developing countries. The Brucella melitensis (B. melitensis) M5-90 vaccine strain (M5-90) has been used on a large scale in China, but may cause abortions if given to pregnant goats or sheep subcutaneously during the late stages of gestation. Moreover, the vaccine M5-90 cannot differentiate natural from vaccinated infection. Therefore, a safer and more potent M5-90 vaccine is required. In this study, a vjbR mutant of M5-90 (M5-90Δ vjbR) was constructed and overcame these drawbacks. M5-90Δ vjbR strain showed reduced survival capability in murine macrophages (RAW 264.7) and BALB/c mice and induced high protective immunity in mice. In addition, M5-90Δ vjbR induced an anti- Brucella -specific immunoglobulin G (IgG) response and stimulated the expression of gamma interferon (INF-γ) and interleukin-4 (IL-4) in vaccinated mice. Furthermore, M5-90Δ vjbR induced IgG response and stimulated the secretion of IFN-γ and IL-4 in immunized sheep. Moreover, the VjbR antigen allowed serological differentiation between infected and vaccinated animals. These results suggest that M5-90Δ vjbR is an ideal live attenuated and efficacious live vaccine candidate against B. melitensis 16 M infection. Highlights • The M5-90Δ vjbR has low virulence in macrophages and mice. • The M5-90Δ vjbR can elicit an anti- Brucella -specific IgG response. • M5-90Δ vjbR imunizations induce a cellular response. • M5-90Δ vjbR imunizations induces protection against B. melitensis challenge. • M5-90Δ vjbR could be a potential DIVA vaccine. [ABSTRACT FROM AUTHOR]