The predicted ABC transporter AbcEDCBA is required for type IV secretion system expression and lysosomal evasion by Brucella ovis

Pathogenesis of Brucella ovis in pregnant mice and protection induced by the candidate vaccine strain B. Ovis ΔabcBA

Ovine brucellosis caused by Brucella ovis is a major cause of reproductive failure in sheep. This study aimed to evaluate transplacental infection and pathogenicity of B.ovis wild type strain ATCC 25,840 (WT B.ovis) and the candidate vaccine strain B.ovis ΔabcBA in pregnant mice. A total of 40 BALB/c mice were equally divided into 4 groups: (i) non immunized and uninfected control mice (3/10 mice became pregnant); (ii) non immunized and challenged with WT B.ovis (5/10 pregnant); (iii) inoculated only with B.ovis ΔabcBA (6/10 pregnant); (iv) immunized with B.ovis ΔabcBA and challenged with WT B.ovis (5/10 pregnant). Female mice bred, and five days after visualization of the vaginal plug, they were inoculated intraperitoneally (ip) with 100 µL of sterile PBS, 100 µL of 1 × 10⁶ CFU of B.ovis ΔabcBA, or 100 µL of 1 × 10⁶ CFU of B.ovis WT, according to each group. At the 17th day of gestation, samples of spleen, liver, uterus, placenta, fetus and mammary gland were obtained for bacteriology, histopathology and immunohistochemistry. Non immunized mice challenged with B.ovis WT developed necrotizing placentitis as well as microgranulomas in the liver and spleen. These findings support the notion that B.ovis infection in pregnant mice induces lesions that are similar to those caused by B.abortus in the same animal model. B.ovis ΔabcBA was not recovered from any of the sampled organs, and it did not cause any gross or microscopic lesions, indicating that it is a safe and attenuated strain in this experimental model. In addition, B.ovis ΔabcBA was induced protective immunity as demonstrated by decreased numbers of B.ovis WT in the liver, uterus and fetuses of immunized mice after the challenge with B.ovis WT.

Comparative Review of Brucellosis in Small Domestic Ruminants

Brucella melitensis and Brucella ovis are the primary etiological agents of brucellosis in small domestic ruminants. B. melitensis was first isolated in 1887 by David Bruce in Malta Island from spleens of four soldiers, while B. ovis was originally isolated in Australia and New Zealand in early 1950's from ovine abortion and rams epididymitis. Today, both agents are distributed worldwide: B. melitensis remains endemic and associated with an extensive negative impact on the productivity of flocks in -some regions, and B. ovis is still present in most sheep-raising regions in the world. Despite being species of the same bacterial genus, B. melitensis and B. ovis have extensive differences in their cultural and biochemical characteristics (smooth vs. rough colonial phases, serum and CO2 dependence for in vitro growth, carbohydrate metabolism), host preference (female goat and sheep vs. rams), the outcome of infection (abortion vs. epididymitis), and their zoonotic potential. Some of these differences can be explained at the bacterial genomic level, but the role of the host genome in promoting or preventing interaction with pathogens is largely unknown. Diagnostic techniques and measures to prevent and control brucellosis in small ruminants vary, with B. melitensis having more available tools for detection and prevention than B. ovis. This review summarizes and analyzes current available information on: (1) the similarities and differences between these two etiological agents of brucellosis in small ruminants, (2) the outcomes after their interaction with different preferred hosts and current diagnostic methodologies, (3) the prevention and control measures, and (4) alerting animal producers about the disease and raise awareness in the research community for future innovative activities.

Transcriptome Landscape of Intracellular Brucella ovis Surviving in RAW264.7 Macrophage Immune System

Brucella ovis infection results in genital damage and epididymitis in rams, placental inflammation and rare abortion in ewes, and neonatal mortality in lambs. However, the mechanism underlying B. ovis infection remains unclear. In the present study, we used prokaryotic transcriptome sequencing to identify the differentially expressed genes (DEGs) between wild-type B. ovis and intracellular B. ovis in RAW264.7 macrophages. Gene ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed, and quantitative reverse transcriptase PCR (qRT-PCR) was used to validate the top 10 upregulated and downregulated DEGs. The results showed that 212 genes were differentially expressed, including 68 upregulated and 144 downregulated genes, which were mainly enriched in 30 GO terms linked to biological process, cellular component, and molecular function. KEGG analysis showed that the DEGs were enriched in the hypoxia-inducible factor 1 (HIF-1) signaling pathway, mitogen-activated protein kinase (MAPK) signaling pathway, beta-alanine metabolism, and quorum sensing pathway. BME_RS01160, BME_RS04270, BME_RS08185, BME_RS12880, BME_RS25875, predicted_RNA865, and predicted_RNA953 were confirmed with the transcriptome sequencing data. Hence, our findings not only reveal the intracellular parasitism of B. ovis in the macrophage immune system, but also help to understand the mechanism of chronic B. ovis infection.

When the Going Gets Rough: The Significance of Brucella Lipopolysaccharide Phenotype in Host-Pathogen Interactions

Brucella is a facultatively intracellular bacterial pathogen and the cause of worldwide zoonotic infections, infamous for its ability to evade the immune system and persist chronically within host cells. Despite the frequent association with attenuation in other Gram-negative bacteria, a rough lipopolysaccharide phenotype is retained by Brucella canis and Brucella ovis, which remain fully virulent in their natural canine and ovine hosts, respectively. While these natural rough strains lack the O-polysaccharide they, like their smooth counterparts, are able to evade and manipulate the host immune system by exhibiting low endotoxic activity, resisting destruction by complement and antimicrobial peptides, entering and trafficking within host cells along a similar pathway, and interfering with MHC-II antigen presentation. B. canis and B. ovis appear to have compensated for their roughness by alterations to their outer membrane, especially in regards to outer membrane proteins. B. canis, in particular, also shows evidence of being less proinflammatory in vivo, suggesting that the rough phenotype may be associated with an enhanced level of stealth that could allow these pathogens to persist for longer periods of time undetected. Nevertheless, much additional work is required to understand the correlates of immune protection against the natural rough Brucella spp., a critical step toward development of much-needed vaccines. This review will highlight the significance of rough lipopolysaccharide in the context of both natural disease and host–pathogen interactions with an emphasis on natural rough Brucella spp. and the implications for vaccine development.

Uncovering the Hidden Credentials of Brucella Virulence

Bacteria in the genus Brucella are important human and veterinary pathogens. The abortion and infertility they cause in food animals produce economic hardships in areas where the disease has not been controlled, and human brucellosis is one of the world's most common zoonoses. Brucella strains have also been isolated from wildlife, but we know much less about the pathobiology and epidemiology of these infections than we do about brucellosis in domestic animals. The brucellae maintain predominantly an intracellular lifestyle in their mammalian hosts, and their ability to subvert the host immune response and survive and replicate in macrophages and placental trophoblasts underlies their success as pathogens. We are just beginning to understand how these bacteria evolved from a progenitor alphaproteobacterium with an environmental niche and diverged to become highly host-adapted and host-specific pathogens. Two important virulence determinants played critical roles in this evolution: (i) a type IV secretion system that secretes effector molecules into the host cell cytoplasm that direct the intracellular trafficking of the brucellae and modulate host immune responses and (ii) a lipopolysaccharide moiety which poorly stimulates host inflammatory responses. This review highlights what we presently know about how these and other virulence determinants contribute to Brucella pathogenesis. Gaining a better understanding of how the brucellae produce disease will provide us with information that can be used to design better strategies for preventing brucellosis in animals and for preventing and treating this disease in humans.

The candidate vaccine strain Brucella ovis ∆abcBA is protective against Brucella melitensis infection in mice

Brucellosis is a major zoonotic disease, and Brucella melitensis is the species most often associated with human infection. Vaccination is the most efficient tool for controlling animal brucellosis, with a consequent decrease of incidence of human infections. Commercially available live attenuated vaccines provide some degree of protection, but retain residual pathogenicity to human and animals. In this study, Brucella ovis ∆abcBA (Bo∆abcBA), a live attenuated candidate vaccine strain, was tested in two formulations (encapsulated with alginate and alginate plus vitelline protein B [VpB]) to immunize mice against experimental challenge with B. melitensis strain 16M. One week after infection, livers and spleens of immunized mice had reduced numbers of the challenge strain B. melitensis 16M when compared with those of nonimmunized mice, with a reduction of approximately 1-log₁₀ of B. melitensis 16M count in the spleens from immunized mice. Moreover, splenocytes stimulated with B. melitensis antigens in vitro secreted IFN-γ when mice had been immunized with Bo∆abcBA encapsulated with alginate plus VpB, but not with alginate alone. Body and liver weights were similar among groups, although spleens from mice immunized with Bo∆abcBA encapsulated with alginate were larger than those immunized with Bo∆abcBA encapsulated with alginate plus VpB or nonimmunized mice. This study demonstrated that two vaccine formulations containing Bo∆abcBA protected mice against experimental challenge with B. melitensis.

Pan-Proteomic Analysis and Elucidation of Protein Abundance among the Closely Related Brucella Species, Brucella abortus and Brucella melitensis

Brucellosis is a zoonotic infection caused by bacteria of the genus Brucella. The species, B. abortus and B. melitensis, major causative agents of human brucellosis, share remarkably similar genomes, but they differ in their natural hosts, phenotype, antigenic, immunogenic, proteomic and metabolomic properties. In the present study, label-free quantitative proteomic analysis was applied to investigate protein expression level differences. Type strains and field strains were each cultured six times, cells were harvested at a midlogarithmic growth phase and proteins were extracted. Following trypsin digestion, the peptides were desalted, separated by reverse-phase nanoLC, ionized using electrospray ionization and transferred into an linear trap quadrapole (LTQ) Orbitrap Velos mass spectrometer to record full scan MS spectra (m/z 300–1700) and tandem mass spectrometry (MS/MS) spectra of the 20 most intense ions. Database matching with the reference proteomes resulted in the identification of 826 proteins. The Cluster of Gene Ontologies of the identified proteins revealed differences in bimolecular transport and protein synthesis mechanisms between these two strains. Among several other proteins, antifreeze proteins, Omp10, superoxide dismutase and 30S ribosomal protein S14 were predicted as potential virulence factors among the proteins differentially expressed. All mass spectrometry data are available via ProteomeXchange with identifier PXD006348.

Brucella ovis mutant in ABC transporter protects against Brucella canis infection in mice and it is safe for dogs

BACKGROUND/OBJECTIVES

Vaccination is the most important tool for controlling brucellosis, but currently there is no vaccine available for canine brucellosis, which is a zoonotic disease of worldwide distribution caused by Brucella canis. This study aimed to evaluate protection and immune response induced by Brucella ovis ΔabcBA (BoΔabcBA) encapsulated with alginate against the challenge with Brucella canis in mice and to assess the safety of this strain for dogs.

METHODS

Intracellular growth of the vaccine strain BoΔabcBA was assessed in canine and ovine macrophages. Protection induced by BoΔabcBA against virulent Brucella canis was evaluated in the mouse model. Safety of the vaccine strain BoΔabcBA was assessed in experimentally inoculated dogs.

RESULTS

Wild type B. ovis and B. canis had similar internalization and intracellular multiplication profiles in both canine and ovine macrophages. The BoΔabcBA strain had an attenuated phenotype in both canine and ovine macrophages. Immunization of BALB/c mice with alginate-encapsulated BoΔabcBA (108 CFU) induced lymphocyte proliferation, production of IL-10 and IFN-γ, and protected against experimental challenge with B. canis. Dogs immunized with alginate-encapsulated BoΔabcBA (109 CFU) seroconverted, and had no hematologic, biochemical or clinical changes. Furthermore, BoΔabcBA was not detected by isolation or PCR performed using blood, semen, urine samples or vaginal swabs at any time point over the course of this study. BoΔabcBA was isolated from lymph nodes near to the site of inoculation in two dogs at 22 weeks post immunization.

CONCLUSION

Encapsulated BoΔabcBA protected mice against experimental B. canis infection, and it is safe for dogs. Therefore, B. ovis ΔabcBA has potential as a vaccine candidate for canine brucellosis prevention.

Evaluation of human trophoblasts and ovine testis cell lines for the study of the intracellular pathogen Brucella ovis

Since pathogenic Brucella survive and replicate inside phagocytes, cellular models of infection constitute important tools in brucellosis research. We describe the behavior of B. ovis PA (which causes a type of ovine brucellosis mainly affecting the male reproductive tract) and representative attenuated mutants in two commercially available cell lines of non-professional phagocytes related to Brucella tissue preference: OA3.Ts ovine testis cells and JEG-3 human trophoblasts. In comparison with J774.A1 macrophages and HeLa cells, intracellular bacteria were enumerated at several post-infection time points and visualized by confocal microscopy. Replication of B. ovis in OA3.Ts and JEG-3 cells was equivalent to that observed in J774.A1 macrophages-despite the more efficient internalization in the latter-and better than in HeLa cells. Multiplication and/or survival in all phagocytes was dependent on virB2 and vjbR but independent of cgs, despite the attenuation in mice of the Δcgs mutant. However, Omp25c was required for B. ovis internalization only in HeLa cells, and removal of Omp31 increased bacterial internalization in human HeLa and JEG-3 cells. The results presented here demonstrate variability in the interaction of B. ovis with different host cells and provide advantageous models of non-professional phagocytes to study the intracellular behavior of B. ovis.

Investigation of host-pathogen interaction between Burkholderia pseudomallei and autophagy-related protein LC3 using hydrophobic chromatography-based technique

BACKGROUND

Burkholderia pseudomallei is an intracellular bacteria causing Melioidosis, the disease widely disseminates in Southeast Asia and Northern Australia. B. pseudomallei has ability to invade various types of host cell and to interfere with host defense mechanisms, such as nitric oxide (NO). Due to the cross-talk among alternative killing mechanisms in host immune response against invading microbes, autophagy is the molecular mechanism belonging to intracellular elimination of eukaryotic cells that has been widely discussed. However, bacterial evasion strategy of B. pseudomallei and host-bacterial protein-protein interaction within autophagic machinery remain unknown.

METHODS

Here, we demonstrated the protein-protein interaction study between different strains of B. pseudomallei, including wild type PP844 and rpoS mutant, with autophagy-related protein LC3 that has been constructed, using the modified immunoaffinity hydrophobic chromatography based-technique. Liquid chromatography tandem-mass spectrometry (LC-MS/MS) analysis was utilized for identifying the eluted proteins obtained from the established column. In addition, the expression level of gene encoding candidate protein was predicted prior to verification using real-time quantitative reverse transcription PCR assay (RT-qPCR).

RESULTS

LC3 recombinant proteins could be entrapped inside the column before encountering their bacterial interacting partners. Based on affinity interaction, the binding capacity of LC3 with antibody displayed over 50% readily for hydrophobically binding with bacterial proteins. Following protein identification, bacterial ATP-binding cassette (ABC) transporter periplasmic substrate-binding protein (BPSL2203) was identified as a candidate LC3-interacting protein, which was found only in B. pseudomallei wild type. Gene expression analysis and bioinformatics of BPSL2203 were validated the proteomic result which are suggesting the role of RpoS-dependent gene regulation.

CONCLUSIONS

Remarkably, utilization of the modified immunoaffinity hydrophobic chromatography with LC-MS/MS is a convenient and reliable approach to a study in B. pseudomallei-LC3 protein-protein interaction.

Meta-Analysis and Advancement of Brucellosis Vaccinology

Background/Objectives

In spite of all the research effort for developing new vaccines against brucellosis, it remains unclear whether these new vaccine technologies will in fact become widely used. The goal of this study was to perform a meta-analysis to identify parameters that influence vaccine efficacy as well as a descriptive analysis on how the field of Brucella vaccinology is advancing concerning type of vaccine, improvement of protection on animal models over time, and factors that may affect protection in the mouse model.

Methods

A total of 117 publications that met the criteria were selected for inclusion in this study, with a total of 782 individual experiments analyzed.

Results

Attenuated (n = 221), inactivated (n = 66) and mutant (n = 102) vaccines provided median protection index above 2, whereas subunit (n = 287), DNA (n = 68), and vectored (n = 38) vaccines provided protection indexes lower than 2. When all categories of experimental vaccines are analyzed together, the trend line clearly demonstrates that there was no improvement of the protection indexes over the past 30 years, with a low negative and non significant linear coefficient. A meta-regression model was developed including all vaccine categories (attenuated, DNA, inactivated, mutant, subunit, and vectored) considering the protection index as a dependent variable and the other parameters (mouse strain, route of vaccination, number of vaccinations, use of adjuvant, challenge Brucella species) as independent variables. Some of these variables influenced the expected protection index of experimental vaccines against Brucella spp. in the mouse model.

Conclusion

In spite of the large number of publication over the past 30 years, our results indicate that there is not clear trend to improve the protective potential of these experimental vaccines.

The ABC transporter YejABEF is required for resistance to antimicrobial peptides and the virulence of Brucella melitensis

The ability to resist the killing effects of host antimicrobial peptides (AMPs) plays a vital role in the virulence of pathogens. The Brucella melitensis NI genome has a gene cluster that encodes ABC transport. In this study, we constructed yejA1, yejA2, yejB, yejE, yejF, and whole yej operon deletion mutants, none of which exhibited discernible growth defect in TSB or minimal medium. Unlike their parental strain, the mutants showed a significantly increased sensitivity to acidic stress. The NIΔyejE and NIΔyejABEF mutants were also more sensitive than B. melitensis NI to polymyxin B, and the expression of yej operon genes was induced by polymyxin B. Moreover, cell and mouse infection assays indicated that NIΔyejE and NIΔyejABEF have restricted invasion and replication abilities inside macrophages and are rapidly cleared from the spleens of infected mice. These findings indicate that the ABC transporter YejABEF is required for the virulence of Brucella, suggesting that resistance to host antimicrobials is a key mechanism for Brucella to persistently survive in vivo. This study provided insights that led us to further investigate the potential correlation of AMP resistance with the mechanisms of immune escape and persistent infection by pathogens.

Comparative transcriptome analysis of Brucella melitensis in an acidic environment: Identification of the two-component response regulator involved in the acid resistance and virulence of Brucella

Brucella melitensis, encounters a very stressful environment in phagosomes, especially low pH levels. So identifying the genes that contribute to the replication and survival within an acidic environment is critical in understanding the pathogenesis of the Brucella bacteria. In our research, comparative transcriptome with RNA-seq were used to analyze the changes of genes in normal-medium culture and in pH4.4-medium culture. The results reveal that 113 genes expressed with significant differences (|log2Ratio| ≥ 3); about 44% genes expressed as up-regulated. With GO term analysis, structural constituent of the ribosome, rRNA binding, structural molecule activity, and cation-transporting ATPase activity were significantly enriched (p-value ≤ 0.05). These genes distributed in 51 pathways, in which ribosome and photosynthesis pathways were significantly enriched. Six pathways (oxidative phosphorylation, iron-transporting, bacterial secretion system, transcriptional regulation, two-component system, and ABC transporters pathways) tightly related to the intracellular survival and virulence of Brucella were analyzed. A two-component response regulator gene in the transcriptional regulation pathway, identified through gene deletion and complementary technologies, played an important role in the resistance to the acid-resistance and virulence of Brucella.

Brucella canis is an intracellular pathogen that induces a lower proinflammatory response than smooth zoonotic counterparts

Canine brucellosis caused by Brucella canis is a disease of dogs and a zoonotic risk. B. canis harbors most of the virulence determinants defined for the genus, but its pathogenic strategy remains unclear since it has not been demonstrated that this natural rough bacterium is an intracellular pathogen. Studies of B. canis outbreaks in kennel facilities indicated that infected dogs displaying clinical signs did not present hematological alterations. A virulent B. canis strain isolated from those outbreaks readily replicated in different organs of mice for a protracted period. However, the levels of tumor necrosis factor alpha, interleukin-6 (IL-6), and IL-12 in serum were close to background levels. Furthermore, B. canis induced lower levels of gamma interferon, less inflammation of the spleen, and a reduced number of granulomas in the liver in mice than did B. abortus. When the interaction of B. canis with cells was studied ex vivo, two patterns were observed, a predominant scattered cell-associated pattern of nonviable bacteria and an infrequent intracellular replicative pattern of viable bacteria in a perinuclear location. The second pattern, responsible for the increase in intracellular multiplication, was dependent on the type IV secretion system VirB and was seen only if the inoculum used for cell infections was in early exponential phase. Intracellular replicative B. canis followed an intracellular trafficking route undistinguishable from that of B. abortus. Although B. canis induces a lower proinflammatory response and has a stealthier replication cycle, it still displays the pathogenic properties of the genus and the ability to persist in infected organs based on the ability to multiply intracellularly.

The abcEDCBA-Encoded ABC Transporter and the virB Operon-Encoded Type IV Secretion System of Brucella ovis Are Critical for Intracellular Trafficking and Survival in Ovine Monocyte-Derived Macrophages

Brucella ovis infection is associated with epididymitis, orchitis and infertility in rams. Most of the information available on B. ovis and host cell interaction has been generated using murine macrophages or epithelial cell lines, but the interaction between B. ovis and primary ovine macrophages has not been studied. The aim of this study was to evaluate the role of the B. ovis abcEDCBA-encoded ABC transporter and the virB operon-encoded Type IV Secretion System (T4SS) during intracellular survival of B. ovis in ovine peripheral blood monocyte-derived macrophages. ΔabcBA and ΔvirB2 mutant strains were unable to survive in the intracellular environment when compared to the WT B. ovis at 48 hours post infection (hpi). In addition, these mutant strains cannot exclude the lysosomal marker LAMP1 from its vacuolar membrane, and their vacuoles do not acquire the endoplasmic reticulum marker calreticulin, which takes place in the WT B. ovis containing vacuole. Higher levels of nitric oxide production were observed in macrophages infected with WT B. ovis at 48 hpi when compared to macrophages infected with the ΔabcBA or ΔvirB2 mutant strains. Conversely, higher levels of reactive oxygen species were detected in macrophages infected with the ΔabcBA or ΔvirB2 mutant strains at 48 hpi when compared to macrophages infected with the WT strain. Our results demonstrate that B. ovis is able to persist and multiply in ovine macrophages, while ΔabcBA and ΔvirB2 mutations prevent intracellular multiplication, favor phagolysosome fusion, and impair maturation of the B. ovis vacuole towards an endoplasmic reticulum-derived compartment.

Encapsulated Brucella ovis Lacking a Putative ATP-Binding Cassette Transporter (ΔabcBA) Protects against Wild Type Brucella ovis in Rams

This study aimed to evaluate protection induced by the vaccine candidate B. ovis ΔabcBA against experimental challenge with wild type B. ovis in rams. Rams were subcutaneously immunized with B. ovis ΔabcBA encapsulated with sterile alginate or with the non encapsulated vaccine strain. Serum, urine, and semen samples were collected during two months after immunization. The rams were then challenged with wild type B. ovis (ATCC25840), and the results were compared to non immunized and experimentally challenged rams. Immunization, particularly with encapsulated B. ovis ΔabcBA, prevented infection, secretion of wild type B. ovis in the semen and urine, shedding of neutrophils in the semen, and the development of clinical changes, gross and microscopic lesions induced by the wild type B. ovis reference strain. Collectively, our data indicates that the B. ovis ΔabcBA strain is an exceptionally good vaccine strain for preventing brucellosis caused by B. ovis infection in rams.

Protection Provided by an Encapsulated Live Attenuated ΔabcBA Strain of Brucella ovis against Experimental Challenge in a Murine Model

This study aimed to evaluate the Brucella ovis ΔabcBA strain as a vaccine candidate in the murine model. BALB/c mice were subcutaneously or intraperitoneally immunized with a single dose or three doses of the B. ovis ΔabcBA strain and then were challenged with wild-type B. ovis. Single or multiple immunizations provided only mild protection, with significantly smaller numbers of wild-type B. ovis CFU in the livers of immunized mice but not in the spleens. Encapsulation of B. ovis ΔabcBA significantly improved protection against experimental challenges in both BALB/c and C57BL/6 mice. Furthermore, immunization with encapsulated B. ovis ΔabcBA markedly prevented lesions in the spleens and livers of experimentally challenged mice. These results demonstrated that the encapsulated B. ovis ΔabcBA strain confers protection to mice; therefore, this strain has potential as a vaccine candidate for rams.