Laboratory animal models for brucellosis research

Influenza viral vectors expressing the Brucella OMP16 or L7/L12 proteins as vaccines against B. abortus infection

BACKGROUND

We generated novel, effective candidate vaccine against Brucella abortus based on recombinant influenza viruses expressing the Brucella ribosomal protein L7/L12 or outer membrane protein (Omp)-16 from the NS1 open reading frame. The main purpose of this work was to evaluate the safety, immunogenicity and protectiveness of vaccine candidate in laboratory animals.

METHODS AND RESULTS

Four recombinant influenza A viral constructs of the subtypes Н5N1 or H1N1 expressing the Brucella proteins L7/L12 or Omp16 were obtained by a reverse genetics method: Flu-NS1-124-L7/L12-H5N1, Flu-NS1-124-Omp16-H5N1, Flu-NS1-124-L7/L12-H1N1 and Flu-NS1-124-Omp16-H1N1. Despite of substantial modification of NS1 gene, all constructs replicated well and were retain their Brucella inserts over five passages in embryonated chicken eggs (CE). Administration of the mono- or bivalent vaccine formulation via prime-boost intranasal (i.n.), conjunctival (c.) or subcutaneous (s.c.) immunization was safe in mice; no deaths, body weight loss or pathomorphological changes were observed over 56 days. Moreover, guinea pigs vaccinated i.n. with vaccine vectors did not shed the vaccine viruses through their upper respiratory tract after the prime and booster vaccination. These findings confirmed the replication-deficient phenotype of viral vectors. The highest antibody response to Brucella antigen was obtained with constructs expressing L7/L12 (ELISA, GMT 242.5-735.0); whereas the highest T-cell immune response- with construct expressing Omp16 (ELISPOT, 337 ± 52-651 ± 45 spots/4×105cells), which was comparable (P > 0.05) to the response induced by the commercial vaccine B. abortus 19. Interestingly, c. immunization appeared to be optimal for eliciting T-cell immune response. In guinea pigs, the highest protective efficacy after challenge with B. abortus 544 was achieved with Omp16 expressing constructs in both monovalent or bivalent vaccine formulations; protective efficacy was comparable to those induced by a commercial live B. abortus 19 vaccine.

CONCLUSION

Thus, influenza vectors expressing Brucella protective antigens can be developed as novel influenza vectored vaccine against B. abortus infection.

Characterization of betaine aldehyde dehydrogenase (BetB) as an essential virulence factor of Brucella abortus

The pathogenic mechanisms of Brucellosis used to adapt to the harsh intracellular environment of the host cell are not fully understood. The present study investigated the in vitro and in vivo characteristics of B. abortus betaine aldehyde dehydrogenase (BetB) (Gene Bank ID: 006932) using a betB deletion mutant constructed from virulent B. abortus 544. In test under stress conditions, including osmotic- and acid stress-resistance, the betB mutant had a lower osmotic-resistance than B. abortus wild-type. In addition, the betB mutant showed higher internalization rates compared to the wild-type strain; however, it also displayed replication failures in HeLa cells and RAW 264.7 macrophages. During internalization, compared to the wild-type strain, the betB mutant was more adherent to the host surface and showed enhanced phosphorylation of protein kinases, two processes that promote phagocytic activity, in host cells. During intracellular trafficking, colocalization of B. abortus-containing phagosomes with LAMP-1 was elevated in betB mutant-infected cells compared to the wild-type cells. In mice, the betB mutant was predominantly cleared from spleens compared to the wild-type strain after 2 weeks post-infection, and the vaccination test with the live betB mutant showed effective protection against challenge infection with the virulent wild-type strain. These findings suggested that the B. abortus betB gene substantially affects the phagocytic pathway in human phagocytes and in host cells in mice. Furthermore, this study highlights the potential use of the B. abortus betB mutant as a live vaccine for the control of brucellosis.

Brucella ovis lacking a species-specific putative ATP-binding cassette transporter is attenuated but immunogenic in rams

Ovine brucellosis caused by Brucella ovis is considered one of the most important reproductive diseases of rams worldwide. This study aimed to characterize the kinetics of infection of a ΔabcAB B. ovis mutant strain in rams. Twelve 1-year-old crossbred rams were used. Six rams were challenged with 2 mL of a suspension containing 1.2×10(9) CFU/mL of B. ovis strain ATCC25840 (wild type) by intraprepucial inoculation and additional 50 μL in each conjunctival sac of a suspension containing 1.2×10(10) CFU/mL of the same strain. The other six rams were challenged with an equivalent number of CFU of the mutant strain ΔabcAB B. ovis through the same routes. Serum samples for serology and semen and urine samples for bacteriologic culture and PCR were collected weekly during 24 weeks. At 24 weeks post infection, tissue samples were collected for bacteriologic culture and PCR. All rams inoculated with wild type or the ΔabcAB strain seroconverted at the fourth week post infection, remaining positive up to the 16th week post infection. PCR and bacteriology demonstrated that only rams inoculated with the wild type strain shed the organism in semen and urine. Lymphocytes from rams inoculated with wild type or ΔabcAB B. ovis had significantly higher proliferation in response to B. ovis antigens when compared with unstimulated controls. Tissue bacteriology and PCR detected B. ovis in all rams challenged with the wild type strain, whereas only one ΔabcAB-infected ram had a positive iliac lymph node sample by PCR.

Bartonella and Brucella--weapons and strategies for stealth attack

Bartonella spp. and Brucella spp. are closely related α-proteobacterial pathogens that by distinct stealth-attack strategies cause chronic infections in mammals including humans. Human infections manifest by a broad spectrum of clinical symptoms, ranging from mild to fatal disease. Both pathogens establish intracellular replication niches and subvert diverse pathways of the host's immune system. Several virulence factors allow them to adhere to, invade, proliferate, and persist within various host-cell types. In particular, type IV secretion systems (T4SS) represent essential virulence factors that transfer effector proteins tailored to recruit host components and modulate cellular processes to the benefit of the bacterial intruders. This article puts the remarkable features of these two pathogens into perspective, highlighting the mechanisms they use to hijack signaling and trafficking pathways of the host as the basis for their stealthy infection strategies.

Toll-like receptor 4-linked Janus kinase 2 signaling contributes to internalization of Brucella abortus by macrophages

Brucella abortus is an intracellular pathogen that uses a crafty strategy to invade and proliferate within host cells, but the distinct signaling pathways associated with phagocytic mechanisms of B. abortus remain unclear. The present study was performed to test the hypothesis that Toll-like receptor 4 (TLR4)-linked signaling interacting with Janus kinase 2 (JAK2) plays an essential role in B. abortus phagocytosis by macrophages. The effects of TLR4-JAK2 signaling on B. abortus phagocytosis in murine macrophage RAW 264.7 cells were observed through an infection assay and confocal microscopy. We determined that the uptake of B. abortus was negatively affected by the dysfunction of TLR4 and JAK2. F-actin polymerization detected by flow cytometry and F-actin assay was amplified for B. abortus entry, whereas that event was attenuated by the disruption of TLR4 and JAK2. Importantly, JAK2 phosphorylation and actin skeleton reorganization were suppressed immediately after B. abortus infection in bone marrow-derived macrophages (BMDMs) from TLR4(-/-) mice, showing the cooperation of JAK2 with TLR4. Furthermore, small GTPase Cdc42 participated in the intermediate pathway of TLR4-JAK2 signaling on B. abortus phagocytosis. Consequently, TLR4-associated JAK2 activation in the early cellular signaling events plays a pivotal role in B. abortus-induced phagocytic processes in macrophages, implying the pathogenic significance of JAK2-mediated entry. Here, we elucidate that this specific phagocytic mechanism of B. abortus might provide achievable strategies for inhibiting B. abortus invasion.

Meta-analysis of variables affecting mouse protection efficacy of whole organism Brucella vaccines and vaccine candidates

BACKGROUND

Vaccine protection investigation includes three processes: vaccination, pathogen challenge, and vaccine protection efficacy assessment. Many variables can affect the results of vaccine protection. Brucella, a genus of facultative intracellular bacteria, is the etiologic agent of brucellosis in humans and multiple animal species. Extensive research has been conducted in developing effective live attenuated Brucella vaccines. We hypothesized that some variables play a more important role than others in determining vaccine protective efficacy. Using Brucella vaccines and vaccine candidates as study models, this hypothesis was tested by meta-analysis of Brucella vaccine studies reported in the literature.

RESULTS

Nineteen variables related to vaccine-induced protection of mice against infection with virulent brucellae were selected based on modeling investigation of the vaccine protection processes. The variable "vaccine protection efficacy" was set as a dependent variable while the other eighteen were set as independent variables. Discrete or continuous values were collected from papers for each variable of each data set. In total, 401 experimental groups were manually annotated from 74 peer-reviewed publications containing mouse protection data for live attenuated Brucella vaccines or vaccine candidates. Our ANOVA analysis indicated that nine variables contributed significantly (P-value < 0.05) to Brucella vaccine protection efficacy: vaccine strain, vaccination host (mouse) strain, vaccination dose, vaccination route, challenge pathogen strain, challenge route, challenge-killing interval, colony forming units (CFUs) in mouse spleen, and CFU reduction compared to control group. The other 10 variables (e.g., mouse age, vaccination-challenge interval, and challenge dose) were not found to be statistically significant (P-value > 0.05). The protection level of RB51 was sacrificed when the values of several variables (e.g., vaccination route, vaccine viability, and challenge pathogen strain) change. It is suggestive that it is difficult to protect against aerosol challenge. Somewhat counter-intuitively, our results indicate that intraperitoneal and subcutaneous vaccinations are much more effective to protect against aerosol Brucella challenge than intranasal vaccination.

CONCLUSIONS

Literature meta-analysis identified variables that significantly contribute to Brucella vaccine protection efficacy. The results obtained provide critical information for rational vaccine study design. Literature meta-analysis is generic and can be applied to analyze variables critical for vaccine protection against other infectious diseases.

Osteoarticular tissue infection and development of skeletal pathology in murine brucellosis

Brucellosis, a frequent bacterial zoonosis, can produce debilitating chronic disease with involvement of multiple organs in human patients. Whereas acute brucellosis is well studied using the murine animal model, long-term complications of host-pathogen interaction remain largely elusive. Human brucellosis frequently results in persistent, chronic osteoarticular system involvement, with complications such as arthritis, spondylitis and sacroiliitis. Here, we focused on identifying infectious sites in the mouse that parallel Brucella melitensis foci observed in patients. In vivo imaging showed rapid bacterial dispersal to multiple sites of the murine axial skeleton. In agreement with these findings, immunohistochemistry revealed the presence of bacteria in bones and limbs, and in the lower spine vertebrae of the axial skeleton where they were preferentially located in the bone marrow. Surprisingly, some animals developed arthritis in paws and spine after infection, but without obvious bacteria in these sites. The identification of Brucella in the bones of mice corroborates the findings in humans that these osteoarticular sites are important niches for the persistence of Brucella in the host, but the mechanisms that mediate pathological manifestations in these sites remain unclear. Future studies addressing the immune responses within osteoarticular tissue foci could elucidate important tissue injury mediators and Brucella survival strategies.

Progress in Brucella vaccine development

Brucella spp. are zoonotic, facultative intracellular pathogens, which cause animal and human disease. Animal disease results in abortion of fetuses; in humans, it manifests flu-like symptoms with an undulant fever, with osteoarthritis as a common complication of infection. Antibiotic regimens for human brucellosis patients may last several months and are not always completely effective. While there are no vaccines for humans, several licensed live Brucella vaccines are available for use in livestock. The performance of these animal vaccines is dependent upon the host species, dose, and route of immunization. Newly engineered live vaccines, lacking well-defined virulence factors, retain low residual virulence, are highly protective, and may someday replace currently used animal vaccines. These also have possible human applications. Moreover, due to their enhanced safety and efficacy in animal models, subunit vaccines for brucellosis show great promise for their application in livestock and humans. This review summarizes the progress of brucellosis vaccine development and presents an overview of candidate vaccines.

MyD88 and TLR9 are required for early control of Brucella ovis infection in mice

Brucella ovis is an important cause of epididymitis in rams, which results in impaired fertility and economic losses. This study demonstrated the role of TLR during the acute phase of infection in the mouse model. C57BL/6 wild type and TLR2(-/-), TLR4(-/-), TLR9(-/-), and MyD88(-/-) mice were infected with B. ovis and bacteriology, histopathology, and pro-inflammatory gene expression were evaluated at 7days post-infection. MyD88(-/-) mice had higher bacterial loads in the spleen when compared to wild type mice. This enhanced susceptibility was associated with decreased inflammatory response in the liver. TLR9(-/-) mice also had higher bacterial loads when compared to wild type mice, but, surprisingly, they developed stronger inflammatory response. TLR2(-/-) and TLR4(-/-) mice were as susceptible as wild type mice to B. ovis infection. Therefore, MyD88 and TLR9 are required for controlling B. ovis multiplication during the early stages of infection.

The pathophysiology of inhalational brucellosis in BALB/c mice

To characterize the clinical presentation and pathophysiology of inhalational brucellosis, Balb/c mice were challenged with Brucella melitensis 16M in a nose-only aerosol exposure chamber. A low dose of 1000 cfu/animal of B. melitensis resulted in 45% of mice with tissue burdens eight weeks post-challenge. The natural history of brucellosis in mice challenged by higher aerosol doses was examined by serial euthanizing mice over an eight week period. Higher challenge doses of 1.00E+05 and 5.00E+05 cfu resulted in positive blood cultures 14 days post-challenge and bacterial burdens were observed in the lung, liver and/or spleens 14 days post-challenge. In addition, the progression of brucellosis was similar between mice challenged by the intranasal and aerosol routes. The results from this study support the use of the Balb/c aerosol nose-only brucellosis mouse model for the evaluation of therapeutics against inhalational brucellosis.

Effect of exogenous erythritol on growth and survival of Brucella

Erythritol has been considered as an important factor for the pathogenesis of Brucella abortus 2308 and its ability to cause abortion in ruminants. There is a lack of laboratory models to study the Brucella-erythritol relationship, as commonly used murine models do not have erythritol. We tested the effect of exogenous erythritol on the growth of Brucella in iron minimal medium (IMM), in infected macrophage culture and in infected mice to determine if these models can be used to study the relationship between Brucella and erythritol. An effect of erythritol on Brucella growth was only seen in IMM. There appear to be no effect of erythritol on Brucella growth in macrophage cell cultures or in mice. This shows that administration of erythritol to the mice or macrophages cannot mimic the environment in ruminants during pregnancy and thus cannot be used as models to understand the effect of erythritol on Brucella pathogenesis.

Host interferon-γ inducible protein contributes to Brucella survival

Brucella spp. are highly adapted intracellular pathogens of mammals that cause chronic infections while surving and replicating in host monocytes and macrophages. Although monocytes are normally susceptible to infection, pretreatment with pro-inflammatory cytokine interferon-γ (IFN-γ) activates cellular defense mechanisms that increase intracellular killing of Brucella and prevents bacterial replication. We examined the contribution of the IFN-γ inducible GTPase, LRG-47, to B. abortus 2308 infection in in vitro and in vivo murine models. Infecting non-activated macrophages from LRG-47(-/-) mice revealed that loss of this host protein negatively effected the intracellular survival and replication of IgG opsonized B. abortus. In contrast, survival and replication of non-opsonized B. abortus was the same in both C57/B6 and LRG-47(-/-) peritoneal macrophages. Following IFN-γ activation of LRG-47(-/-) monocytes, IgG opsonized B. abortus survived better than non-opsonized bacteria. The differential fate of opsonized and non-opsonized B. abortus was only observed in macrophages collected from LRG-47(-/-) mice. Given the specific nature of the relationship between this host protein and the mechanism of Brucella internalization, LRG-47(-/-) mice were infected with B. abortus to assess whether the loss of the lrg47 protein would affect the ability of the bacteria to colonize or persist within the host. B. abortus were able to establish and maintain similar numbers of bacteria in both C57/B6 mice and LRG-47(-/-) through 3 weeks post intraperitoneal infection. By 9 weeks p.i. fewer B. abortus were recovered from LRG-47(-/-) mice than controls, suggesting that the host protein has a positive role in maintaining long term persistence of the bacteria within the host. These observations demonstrating a positive role for a host IFN-γ induced protein defense protein has yet to be reported. These results provide interesting insight into the complex interaction between Brucella and their host.

In situ microscopy analysis reveals local innate immune response developed around Brucella infected cells in resistant and susceptible mice

Brucella are facultative intracellular bacteria that chronically infect humans and animals causing brucellosis. Brucella are able to invade and replicate in a broad range of cell lines in vitro, however the cells supporting bacterial growth in vivo are largely unknown. In order to identify these, we used a Brucella melitensis strain stably expressing mCherry fluorescent protein to determine the phenotype of infected cells in spleen and liver, two major sites of B. melitensis growth in mice. In both tissues, the majority of primary infected cells expressed the F4/80 myeloid marker. The peak of infection correlated with granuloma development. These structures were mainly composed of CD11b⁺ F4/80⁺ MHC-II⁺ cells expressing iNOS/NOS2 enzyme. A fraction of these cells also expressed CD11c marker and appeared similar to inflammatory dendritic cells (DCs). Analysis of genetically deficient mice revealed that differentiation of iNOS⁺ inflammatory DC, granuloma formation and control of bacterial growth were deeply affected by the absence of MyD88, IL-12p35 and IFN-γ molecules. During chronic phase of infection in susceptible mice, we identified a particular subset of DC expressing both CD11c and CD205, serving as a reservoir for the bacteria. Taken together, our results describe the cellular nature of immune effectors involved during Brucella infection and reveal a previously unappreciated role for DC subsets, both as effectors and reservoir cells, in the pathogenesis of brucellosis.

Internal affairs: investigating the Brucella intracellular lifestyle

Bacteria of the genus Brucella are Gram-negative pathogens of several animal species that cause a zoonotic disease in humans known as brucellosis or Malta fever. Within their hosts, brucellae reside within different cell types where they establish a replicative niche and remain protected from the immune response. The aim of this article is to discuss recent advances in the field in the specific context of the Brucella intracellular 'lifestyle'. We initially discuss the different host cell targets and their relevance during infection. As it represents the key to intracellular replication, the focus is then set on the maturation of the Brucella phagosome, with particular emphasis on the Brucella factors that are directly implicated in intracellular trafficking and modulation of host cell signalling pathways. Recent data on the role of the type IV secretion system are discussed, novel effector molecules identified and how some of them impact on trafficking events. Current knowledge on Brucella gene regulation and control of host cell death are summarized, as they directly affect intracellular persistence. Understanding how Brucella molecules interplay with their host cell targets to modulate cellular functions and establish the intracellular niche will help unravel how this pathogen causes disease.

BmaC, a novel autotransporter of Brucella suis, is involved in bacterial adhesion to host cells

Brucella is an intracellular pathogen responsible of a zoonotic disease called brucellosis. Brucella survives and proliferates within several types of phagocytic and non-phagocytic cells. Like in other pathogens, adhesion of brucellae to host surfaces was proposed to be an important step in the infection process. Indeed, Brucella has the capacity to bind to culture human cells and key components of the extracellular matrix, such as fibronectin. However, little is known about the molecular bases of Brucella adherence. In an attempt to identify bacterial genes encoding adhesins, a phage display library of Brucella suis was panned against fibronectin. Three fibronectin-binding proteins of B. suis were identified using this approach. One of the candidates, designated BmaC was a very large protein of 340 kDa that is predicted to belong to the type I (monomeric) autotransporter family. Microscopy studies showed that BmaC is located at one pole on the bacterial surface. The phage displaying the fibronectin-binding peptide of BmaC inhibited the attachment of brucellae to both, HeLa cells and immobilized fibronectin in vitro. In addition, a bmaC deletion mutant was impaired in the ability of B. suis to attach to immobilized fibronectin and to the surface of HeLa and A549 cells and was out-competed by the wild-type strain in co-infection experiments. Finally, anti-fibronectin or anti-BmaC antibodies significantly inhibited the binding of wild-type bacteria to HeLa cells. Our results highlight the role of a novel monomeric autotransporter protein in the adhesion of B. suis to the extracellular matrix and non-phagocytic cells via fibronectin binding.

Extended safety and efficacy studies of the attenuated Brucella vaccine candidates 16 M(Delta)vjbR and S19(Delta)vjbR in the immunocompromised IRF-1-/- mouse model

The global distribution of brucellosis and high incidence in certain areas of the world warrant the development of a safer and efficacious vaccine. For the past 10 years, we have focused our attention on the development of a safer, but still highly protective, live attenuated vaccine for human and animal use. We have demonstrated the safety and protective efficacy of the vaccine candidates 16 MΔvjbR and S19ΔvjbR against homologous and heterologous challenge in multiple immunocompetent animal models, including mice and deer. In the present study, we conducted a series of experiments to determine the safety of the vaccine candidates in interferon regulatory factor-1-knockout (IRF-1(-/-)) mice. IRF-1(-/-) mice infected with either wild-type Brucella melitensis 16 M or the vaccine strain Brucella abortus S19 succumb to the disease within the first 3 weeks of infection, which is characterized by a marked granulomatous and neutrophilic inflammatory response that principally targets the spleen and liver. In contrast, IRF-1(-/-) mice inoculated with either the 16 MΔvjbR or S19ΔvjbR vaccine do not show any clinical or major pathological changes associated with vaccination. Additionally, when 16 MΔvjbR- or S19ΔvjbR-vaccinated mice are challenged with wild-type Brucella melitensis 16M, the degree of colonization in multiple organs, along with associated pathological changes, is significantly reduced. These findings not only demonstrate the safety and protective efficacy of the vjbR mutant in an immunocompromised mouse model but also suggest the participation of lesser-known mechanisms in protective immunity against brucellosis.

Experimental infection of rabbits (Oryctolagus cuniculus) with Brucella suis biovar 1 isolated from wild hares (Lepus europaeus)

Brucella suis biovar 1 is the causative agent of brucellosis in several domestic and wild animals and it is a common agent of human brucellosis. European hares (Lepus europaeus) have been shown to be infected by B. suis biovar 1 and the transmission to other animals has been suggested. In this work, experimental rabbits (Cuniculus orictolagus) were infected with B. suis biovar 1 isolated from wild hares. Infected rabbits showed high serological response in 2 weeks after discharge and typical granulomatous lesions (2mm diameter) were found in liver, spleen and kidneys after 50 days. B. suis biovar 1 was cultured from the lesion of the organs mentioned above as well as from urine, placenta and fetuses. These data suggest that hares are a potential source for horizontal transmission of B. suis biovar 1 to other mammalians.

Antibodies for biodefense

Potential bioweapons are biological agents (bacteria, viruses, and toxins) at risk of intentional dissemination. Biodefense, defined as development of therapeutics and vaccines against these agents, has seen an increase, particularly in the US following the 2001 anthrax attack. This review focuses on recombinant antibodies and polyclonal antibodies for biodefense that have been accepted for clinical use. These antibodies aim to protect against primary potential bioweapons, or category A agents as defined by the Centers for Disease Control and Prevention (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox virus, and certain others causing viral hemorrhagic fevers) and certain category B agents. Potential for prophylactic use is presented, as well as frequent use of oligoclonal antibodies or synergistic effect with other molecules. Capacities and limitations of antibodies for use in biodefense are discussed, and are generally applicable to the field of infectious diseases.

Roles of genomic island 3 (GI-3) BAB1_0278 and BAB1_0263 open reading frames (ORFs) in the virulence of Brucella abortus in BALB/c mice

The genomic island 3 (GI-3) shared by Brucella melitensis and Brucella abortus contains 29 genes encoding mostly unknown proteins. Within this island, the open reading frames (ORFs) BAB1_0278 and BAB1_0263 are present, BAB1_0278 encodes a hypothetical protein of 64 amino acids sharing a domain with the GcrA superfamily, whereas the amino acid sequence of BAB1_0263 showed 42% identity with an iron regulated Lsr2 protein. We obtained one deletion mutant for each one of these ORFs present within the B. abortus GI-3 named BA-278 and BA-263, respectively. Both mutants were evaluated with respect to their ability to invade and replicate in nonprofessional and professional phagocytes (HeLa and J774.A1 cells) and their virulence in mice. Both mutants invaded efficiently HeLa and J774. A1 cells, however, 48-h post-infection the BA-278 mutant showed a lower intracellular persistence. The deletion of the ORF BAB1_0278, also affected the persistence of B. abortus in the spleens of mice, unlike to the deletion of the ORF BAB1_0263. These results allow us to conclude that BAB1_0278 ORF contributes to virulence of Brucella, since it is necessary to establish an optimal infectious process.