Brucella central carbon metabolism: an update.

The brucellae are facultative intracellular pathogens causing brucellosis, an important zoonosis. Here, we review the nutritional, genetic, proteomic and transcriptomic studies on Brucella carbon uptake and central metabolism, information that is needed for a better understanding of Brucella virulence. There is no uniform picture across species but the studies suggest primary and/or secondary transporters for unknown carbohydrates, lactate, glycerol phosphate, erythritol, xylose, ribose, glucose and glucose/galactose, and routes for their incorporation to central metabolism, including an erythritol pathway feeding the pentose phosphate cycle. Significantly, all brucellae lack phosphoenolpyruvate synthase and phosphofructokinase genes, which confirms previous evidence on glycolysis absence, but carry all Entner-Doudoroff (ED) pathway and Krebs cycle (and glyoxylate pathway) genes. However, glucose catabolism proceeds through the pentose phosphate cycle in the classical species, and the ED pathway operates in some rodent-associated brucellae, suggesting an ancestral character for this pathway in this group. Gluconeogenesis is functional but does not rely exclusively on classical fructose bisphosphatases. Evidence obtained using infection models is fragmentary but suggests the combined or sequential use of hexoses/pentoses, amino acids and gluconeogenic substrates. We also discuss the role of the phosphotransferase system, stringent reponse, quorum sensing, BvrR/S and sRNAs in metabolism control, an essential aspect of the life style of facultative intracellular parasites.

The quest for a true One Health perspective of brucellosis.

One Health is an interdisciplinary collaboration that aims at mitigating risks to human health arising from microorganisms present in non-human animal species, which have the potential to be transmitted and cause disease in humans. Different degrees of scientific collaboration and sectoral integration are needed for different types of zoonotic diseases, depending on the health and associated economic gains that can be expected from a One Health approach. Indeed, mitigating zoonotic risks related to emerging diseases with pandemic potential is different from mitigating risks related to endemic zoonotic diseases like brucellosis. Likewise, management of brucellosis at the wildlife-livestock interface in wildlife conservation areas is in essence different from mitigating transmission of a given Brucella species within its preferential host species, which in turn is different from mitigating the spillover of a given Brucella species to non-preferential host species, humans included. Brucellosis economic models often oversimplify and/or wrongly assess transmission between reservoir hosts and spillover hosts. Moreover,they may not properly value non-market outcomes, such as avoidance of human disease, consumer confidence and conservation biology issues. As a result, uncertainty is such that the economic predictions of these models can be questionable. Therefore, understanding the infection biology of Brucella species is a prerequisite. This paper reviews and highlights important features of the infection biology of Brucella species and the changing epidemiology of brucellosis that need to be integrated into a true One Health perspective of brucellosis.

Brucella melitensis MucR, an orthologue of Sinorhizobium meliloti MucR, is involved in resistance to oxidative, detergent, and saline stresses and cell envelope modifications.

Brucella spp. and Sinorhizobium meliloti are alphaproteobacteria that share not only an intracellular lifestyle in their respective hosts, but also a crucial requirement for cell envelope components and their timely regulation for a successful infectious cycle. Here, we report the characterization of Brucella melitensis mucR, which encodes a zinc finger transcriptional regulator that has previously been shown to be involved in cellular and mouse infections at early time points. MucR modulates the surface properties of the bacteria and their resistance to environmental stresses (i.e., oxidative stress, cationic peptide, and detergents). We show that B. melitensis mucR is a functional orthologue of S. meliloti mucR, because it was able to restore the production of succinoglycan in an S. meliloti mucR mutant, as detected by calcofluor staining. Similar to S. meliloti MucR, B. melitensis MucR also represses its own transcription and flagellar gene expression via the flagellar master regulator ftcR. More surprisingly, we demonstrate that MucR regulates a lipid A core modification in B. melitensis. These changes could account for the attenuated virulence of a mucR mutant. These data reinforce the idea that there is a common conserved circuitry between plant symbionts and animal pathogens that regulates the relationship they have with their hosts.

Use of Mycobacterium avium subsp. paratuberculosis specific coding sequences for serodiagnosis of bovine paratuberculosis.

In this study, the finished complete genome of Mycobacterium avium subsp. paratuberculosis (Map) was screened for specific coding sequences that could be very valuable in the design of a sensitive and specific Map detection serological assay. Eighty-seven Map-specific sequences were retained. Among these, three candidate antigens have been analysed for their serodiagnostic potential. These antigens were selected on the basis of their putative immunogenicity as predicted by in silico analysis. The antigens were cloned in Escherichia coli, expressed, and purified before testing in an antibody detection ELISA test, using a well characterized panel of 18 and 48 sera from Map infected and uninfected cattle, respectively. Two of these antigens, antigen 6 and MAP1637c, yielded in our conditions a sensitivity of 72% and 82%, respectively, for a specificity of 98%. It is particularly noticeable that, when probed with the same serum panel, the most widely used European paratuberculosis commercial seroassay (Pourquier test) yielded a sensitivity of 72% for a specificity of only 92%.

Antigenic properties of peptidic mimics for epitopes of the lipopolysaccharide from Brucella.

The lipopolysaccharide (LPS) is up to now the only identified major virulence determinant of Brucella. This bacterium is responsible for brucellosis in animals and for Malta fever in humans. Several monoclonal antibodies (mAbs) directed against various LPS epitopes have been characterized. Two mAbs, named A15-6B3 and B66-2C8, directed against distinct LPS epitopes have been used to select peptides from 11 phage display libraries. The sequences of the selected peptides contain an overrepresentation of either proline or tryptophan residues when selected with either A15-6B3 or B66-2C8 mAbs, respectively. For the best binding peptides, competition with LPS for the binding to the mAb is detected, which suggests that the peptides bind to the paratope of the mAb. The phages selected from the libraries were used to immunise mice, and a weak antibody response directed against LPS has been observed. These data suggest that a subset of the selected peptides are mimotopes of the LPS epitopes.

B cells from bovine leukemia virus- (BLV) infected sheep with hematological disorders express the CD5 T cell marker.

Though peripheral blood B cells from healthy sheep were known to be devoid of the CD5 T cell marker, it appears from our study that most B cells from bovine leukemia virus- (BLV) infected sheep with hematological disorders express both the CD5 marker and surface IgM. The possible meaning of this T cell marker expression on B cells from BLV-infected sheep is briefly discussed.

CD5+ B cells from bovine leukemia virus infected cows are activated cycling cells responsive to interleukin 2.

Most of the B cells from bovine leukemia virus (BLV) infected cows in persistent lymphocytosis (PL) were known to express the CD5 T-cell marker but it was not known whether this peculiar membrane phenotype relates to an activation state. It was demonstrated that these B cells were also flagged by two other membrane markers normally borne by cells belonging to the myeloid lineage (namely CD11b and CD11c). Moreover, cell cycle analysis illustrated that a significant percentage of these B cells (greater than 15%) left their resting (G0/G1) status and progressed through the cell cycle. In addition, T-cell-depleted peripheral blood mononuclear cells from animals in PL were shown to proliferate in response to a IL-2-containing supernatant (MLA 144). These results indicate that the CD5+ B cells from BLV-infected cows in PL are activated cells.

Cloning and sequencing of the bacterioferritin gene of Brucella melitensis 16M strain.

The 40 N-terminal amino acids of the 20 kDa antigen A2 from Brucella melitensis were sequenced and showed important similarities with 4 bacterioferrins. A monoclonal antibody raised against this antigen cross-reacted with Escherichia coli bacterioferritin. Hybridization of two sets of degenerate primers with B. melitensis HindIII-digested genomic DNA identified a 3.8 kb fragment. This fragment was shown to contain a bacterioferritin gene (bfr) encoding a 161-amino acid protein. The sequence of the Brucella bacterioferritin is 69% similar to that of E. coli, and many of the ferroxidase centre and haem-ligation residues are conserved.

The use of colloidal gold for screening monoclonal antibodies to cell surface antigens.

An immunogold method in Terasaki plates is described which allows accurate and sensitive visualization of the binding of monoclonal antibodies to cell surface antigens and is suitable for large scale screening. Monolayers of fixed cells are prepared in the wells. The binding of monoclonal antibodies is detected by a protein A gold complex. The cell-bound gold can be visualized by either optical or transmission electron microscopy. The results obtained with various monoclonal antibodies are presented.

Adrenaline influence on the immune response. II. Its effects through action on the suppressor T-cells.

Experiments were carried out to specify the adrenaline target among the immunocompetent cells. Adrenaline administered for some hours exerted opposite effects on the natural PFC and RFC: the first were enhanced and the second significantly reduced. These paradoxical results were interpreted as a consequence of the inhibition of the suppressor T-cells in the resting status. Adrenaline appeared to act on the sensitive cells through beta-rather than through alpha-receptors. Further experiments on the adrenaline influence on the syngeneic barrier phenomenon and on the cellular balance at its termination seemed to indicate that adrenaline was directly inhibitory for the Ts but not for their precursors. These results are discussed in the light of the cellular networks regulating the immune response.

Adrenaline influence on the immune response. I. Accelerating or suppressor effects according to the time of application.

The intervention of adrenaline in the immunoregulation was investigated through the modification of the anti-SRBC PFC response of mice after its i.p. administration (4 micrograms) at various intervals before SRBC antigen. When the interval was less than 24 h, adrenaline accelerated the immune kinetics. This modification was apparent on both direct and indirect PFC, as well as on naive and immune mice. However, mice treated from 2 days showed a suppression of the response. The adrenaline effect subsisted on the adoptive response of spleen cells drug-treated either in vivo or in vitro. The mitogenic response after in vitro PHA or LPS stimulation of spleen cells from adrenaline-treated mice indicated that the T-cells were the drug target. The physiological role of the adrenaline and immunological influences of acute stress are discussed in the paper.

Bovine leukemia virus (BLV)-infected B-cells express a marker similar to the CD5 T cell marker.

In the course of generating monoclonal antibodies to bovine thymus-dependent differentiation antigens, we were able to characterize an antibody, termed 8C11, that detects an antigen shared by a majority of thymocytes and peripheral T cells (in blood and thymus-dependent area of spleen and lymph-nodes), but undetectable on normal B cells. However, this antibody was reactive with B cells from cows infected with bovine leukemia virus (BLV). These BLV-infected B cells were found to express simultaneously high concentrations of both surface IgM and 8C11-detected antigen. The antigen recognized by this antibody was shown to be a 67.5 kDa molecule. Because similar findings have been made on mouse myelomas and on human chronic leukemia cells, where this antigen was considered to be the equivalent of mouse Ly-1 antigen and human Leu-1 or CD5 antigen, the T cell antigen detected on BLV-infected cells could be the bovine counterpart of the CD5 antigen. By another way, it has been found that the CD5 T cell antigen is also present on a minor subpopulation of B cells in the spleen but not in the blood. We suggest that in the bovine a similar B cell subpopulation should be the BLV target and expand as a consequence of viral insertion, leading to the persistent lymphocytosis observed on BLV-infected animals.

Selection of phage-displayed peptides recognised by monoclonal antibodies directed against the lipopolysaccharide of Brucella.

Panning and screening of various phage display libraries with monoclonal antibodies (mAbs) directed against the O-chain of the lipopolysaccharide (LPS) of Brucella sp. allowed the identification of peptidic mimotopes of some O-chain epitopes. Four mAbs were tested. The A76-12G12 mAb, which is specific for LPS of all strains of Brucella, either A- or M-dominant, did not yield any peptidic mimotope, despite a specific yield enrichment during the rounds of panning. The B66-4F9 mAb, that recognises an epitope common to both Brucella sp. and Yersinia enterocilitca O:9 strains, allowed the selection of only one phage clone that was shown to be an antigenic but not immunogenic mimotope. The B66-2C8 and A15-6B3 mAbs, respectively, specific for the LPS of A-dominant and M-dominant Brucella sp., yielded several sequences, which allowed the determination of consensus sequences. These consensus will be of high interest for the construction of second generation libraries. For the best binding peptides, competition with LPS for the binding to the mAb is detected, which suggests that the peptides bind to the paratope of the mAb. The phages selected from the libraries were used to immunise mice, and a weak antibody response directed against LPS has been observed for some peptides. These data suggest that a subset of the selected peptides are immunogenic mimotopes of the LPS epitopes.

Conservation of seven genes involved in the biosynthesis of the lipopolysaccharide O-side chain in Brucella spp.

Seven genes of the wb locus of Brucella melitensis 16M involved in the biosynthesis of the lipopolysaccharide O-side chain have been recently identified, i.e. wbkA, gmd, per, wzm, wzt, wbkB, and wbkC, coding, respectively, for proteins homologous to mannosyltransferase, GDP-mannose 4,6 dehydratase, perosamine synthetase, ABC-type transporter (integral membrane protein), ABC-type transporter (ATPase domain), a hypothetical protein of unknown function, and a putative formyl transferase. The seven genes have a G + C content lower (around 48%) than that typical of Brucella spp. (58%) and thus may have been acquired from a species other than Brucella. In the present study, we analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) the seven O-chain biosynthetic genes for polymorphism among Brucella spp. PCR-RFLP showed that the seven genes are highly conserved and occur even in the naturally rough species B. ovis and B. canis and also in rough strains of B. abortus and B. melitensis. Nevertheless, the few polymorphisms that were observed consisted of absence of additional restriction sites sometimes allowing differentiation at the species level (e.g. B. ovis) or at the biovar or strain level. There were no apparent deletions or insertions in the PCR-amplified genes in any of the Brucella strains studied. In conclusion, the seven O-chain biosynthetic genes studied appear to be highly conserved among Brucella spp. and thus may have been acquired before species differentiation. Some of the species- or biovar-specific markers detected could be used for molecular typing of brucellae in addition to those previously described.

Differentiation of Brucella melitensis, B. ovis and B. suis biovar 2 strains by use of membrane protein- or cytoplasmic protein-specific gene probes.

The possibility of differentiating Brucella species and biovars by Southern blot hybridization of agarose gel-electrophoresed HindIII-digested genomic DNA with membrane protein- or cytoplasmic protein-specific gene probes was investigated on 92 reference and field strains representative of all known species and biovars. Based on the RFLP pattern observed, three gene probes, i.e. br25, 39ugpa and omp16 coding for membrane or cytoplasmic proteins differentiated B. melitensis, B. ovis and B. suis biovar 2 strains from each other and from the other Brucella species and biovars. Thus, the use of these specific gene probes could contribute, in addition to previously identified species- or biovar-specific markers, to the molecular identification and typing of Brucella isolates.

Genetic organisation of the lipopolysaccharide O-antigen biosynthesis region of brucella melitensis 16M (wbk).

Brucella spp. are Gram-negative, facultative intracellular bacteria that cause a zoonotic world-wide disease. As in other Gram-negative bacteria, its S-LPS (smooth lipopolysaccharide) is a major determinant of virulence. The Brucella melitensis 16M LPS O-antigen is a homopolymer of 4-formamido-4,6, dideoxymannose. In this study, the previously cloned 14-kb wbk gene cluster was sequenced, and seven open reading frames (ORFs) as well as four insertion sequences were identified. Six of the seven ORFs are homologous to LPS biosynthesis genes from other organisms. The gmd, per and wbkC gene products are predicted to be involved in 4-formamido-4,6,dideoxymannose synthesis. By deletion experiments, we demonstrated that the putative formyltransferase WbkC is absolutely required for the O-side-chain production. The wbkA gene product is similar to several mannosyltransferases and is probably involved in the polymerisation of the B. melitensis O-side-chain. We also identified two genes (wzm and wzt) encoding proteins with high similarity to several two-component ABC (ATP-binding cassette) transporters. Their implication in O-antigen translocation across the inner membrane was confirmed by gene replacement. Finally, no function has been assigned to the wbkB gene either by homology search or functionally, because deletion of wbkB did not interfere with the O-antigen structure. The seven ORFs have a low G + C content, indicating that they might have been acquired by lateral transfer from a progenitor with more A + T rich DNA.

Identification of the major T-cell antigens present in the Brucella melitensis B115 protein preparation, Brucellergene OCB.

Brucellergene is a commercial allergen prepared from Brucella melitensis strain B115 and containing at least 20 cytoplasmic proteins. These proteins were separated by SDS-PAGE. The unstained gel was divided into 18 fractions and proteins were eluted from the gel fractions. The capacity of the separated proteins to elicit delayed-type hypersensitivity (DTH) in infected guinea-pigs or to induce the production of interferon-gamma (IFN-gamma) by blood cells from infected cattle was evaluated. The biological activity of the corresponding protein fractions blotted on to nitrocellulose was measured in a lymphocyte blastogenesis assay. Among the 18 fractions tested, two-spanning the mol. wt ranges 17-22 (fraction 8) and 35-42-kDa (fraction 17)-showed the maximum biological activity in the three tests. These fractions contain two antigens, the Brucella bacterioferritin (BFR) and P39 proteins. Both proteins are good candidates for the detection of cellular immunity to Brucella.

Topology prediction of Brucella abortus Omp2b and Omp2a porins after critical assessment of transmembrane beta strands prediction by several secondary structure prediction methods.

In order to propose a reliable model for Brucella porin topology, several structure prediction methods were evaluated in their ability to predict porin topology. Four porins of known structure were selected as test-cases and their secondary structure delineated. The specificity and sensitivity of 11 methods were separately evaluated. Our critical assessment shows that some secondary structure prediction methods (PHD, Dsc, Sopma) originally designed to predict globular protein structure are useful on porin topology prediction. The overall best prediction is obtained by combining these three "generalist" methods with a transmembrane beta strand prediction technique. This "consensus" method was applied to Brucella porins Omp2b and Omp2a, sharing no sequence homology with any other porin. The predicted topology is a 16-stranded antiparallel beta barrel with Omp2a showing a higher number of negatively charged residue in the exposed loops than Omp2b. Experiments are in progress to validate the proposed topology and the functional hypotheses. The ability of the proposed consensus method to predict topology of complex outer membrane protein is briefly discussed.

Studies on the potential of microparticles entrapping pDNA-poly(aminoacids) complexes as vaccine delivery systems.

Poly(D,L-lactide-co-glycolide) (PLGA) microparticles containing plasmid DNA (pDNA) have potential uses as vaccine delivery systems. Nevertheless, the established double emulsion and solvent evaporation method used to produce them is characterised by a low encapsulation efficiency (about 20%) and nicks the supercoiled DNA. The aim of this work was to develop an encapsulation process to optimise the overall encapsulation efficiency and the supercoiled DNA content, to obtain a carrier suitable for mucosal delivery of DNA vaccines. Our strategy was to reduce the global negative charge of DNA which was unfavourable to its incorporation into the polymer by condensing it with cationic poly(aminoacids) which were previously reported to improve cell transfection. In this study, after characterisation of the compaction of DNA plasmid encoding for a Green Fluorescent Protein, we demonstrated that resulting complexes were successfully encapsulated into PLGA microparticles presenting a mean size around 4.5 microns. The preliminary step of complexation enhances the yield of the process by a factor 4.1 and protects the supercoiled form. In a bacteria transformation assay, we demonstrated that extracted pDNA (naked or complexed) remained in a transcriptionally active form after encapsulation. Bovine macrophages in culture phagocytosed microparticles loaded with uncomplexed/complexed with poly(L-lysine) pDNA. The production of the Green Fluorescent Protein demonstrated that these carriers could deliver intact and functional plasmid DNA probably by escaping from lysosomal degradation.

Infection of cattle with Yersinia enterocolitica O:9 a cause of the false positive serological reactions in bovine brucellosis diagnostic tests.

During the last four years, an increasing number of cattle herds were classified positive by brucellosis screening tests in areas of Belgium and France free of the disease. No clinical symptom of brucellosis was reported in these animals and no Brucella abortus strains were isolated. After two years, no brucellosis outbreak was registered in all of the herds concerned. On this basis, all the serological reactions observed were classified as false positive. An ELISA using Yersinia Outer membrane Proteins (YOPs) as antigens was developed in order to discriminate between a Yersinia enterocolitica O:9 infection and a Brucella abortus infection. Antibodies against YOPs were detected in sera from Y. enterocolitica O:9 experimentally infected cattle (n = 4) but not in sera from B. abortus experimentally infected cattle (n = 4). In a field study, 66.7% of the 174 serum samples from cattle presenting false positive serological reactions showed anti-YOPs antibodies whereas only 10% of 454 sera, classified negative by the brucellosis screening tests, showed anti-YOPs antibodies. Our results suggest that infections with Y. enterocolitica O:9 may cause false positive reactions in brucellosis testing.