Nuestros investigadores

Maite Iriarte Cilveti

Microbiología y Parasitología
Facultad de Medicina. Universidad de Navarra
Líneas de investigación
Interacción entre Yersinia enterocolitica y la célula eucariota., Mecanismos moleculares de patogenicidad de Yersinia., Vacunas frente a la Brucelosis., Mecanismos de patogenicidad de Brucella. Estudio de los lípidos de membrana y del Lipopolisacárido. Interacción de Brucella con célula huésped.
Índice H
25, (Google Scholar, 30/04/2020)
21, (Scopus, 30/04/2020)
21, (WoS, 30/04/2020)

Publicaciones científicas más recientes (desde 2010)

Autores: Aragón Aranda, Beatriz; de Miguel, M. J.; Martínez Gómez, Estrella de Fátima; et al.
ISSN 0928-4249  Vol. 51  Nº 1  2020  págs. 13
Autores: Aragón Aranda, Beatriz; de Miguel, M. J.; Lázaro Antón, Leticia; et al.
ISSN 1297-9716  Vol. 51  Nº 1  2020  págs. 92
Brucella is a genus of gram-negative bacteria that cause brucellosis. B. abortus and B. melitensis infect domestic ruminants while B. suis (biovars 1-3) infect swine, and all these bacteria but B. suis biovar 2 are zoonotic. Live attenuated B. abortus S19 and B. melitensis Rev1 are effective vaccines in domestic ruminants, though both can infect humans. However, there is no swine brucellosis vaccine. Here, we investigated the potential use as vaccines of B. suis biovar 2 rough (R) lipopolysaccharide (LPS) mutants totally lacking O-chain (Bs2¿wbkF) or only producing internal O-chain precursors (Bs2¿wzm) and mutants with a smooth (S) LPS defective in the core lateral branch (Bs2¿wadB and Bs2¿wadD). We also investigated mutants in the pyruvate phosphate dikinase (Bs2¿ppdK) and phosphoenolpyruvate carboxykinase (Bs2¿pckA) genes encoding enzymes bridging phosphoenolpyruvate and the tricarboxylic acid cycle. When tested in the OIE mouse model at the recommended R or S vaccine doses (108 and 105 CFU, respectively), CFU/spleen of all LPS mutants were reduced with respect to the wild type and decreased faster for the R than for the S mutants. At those doses, protection against B. suis was similar for Bs2¿wbkF, Bs2¿wzm, Bs2¿wadB and the Rev1 control (105 CFU). As described before for B. abortus, B. suis biovar 2 carried a disabled pckA so that a double mutant Bs2¿ppdK¿pckA had the same metabolic phenotype as Bs2¿ppdK and ppdK mutation was enough to generate attenuation. At 105 CFU, Bs2¿ppdK also conferred the same protection as Rev1. As compared to other B. suis vaccine candidates described before, the mutants described here simultaneously carry irreversible deletions easy to identify as vaccine markers, lack antibiotic-resistance markers and were obtained in a non-zoonotic background. Since R vaccines should not elicit antibodies to the S-LPS and wzm mutants carry immunogenic O-chain precursors and did not improve Bs2¿wbkF, the latter seems a better R vaccine candidate than Bs2¿wzm. However, taking into account that all R vaccines interfere in ELISA and other widely used assays, whether Bs2¿wbkF is advantageous over Bs2¿wadB or Bs2¿ppdK requires experiments in the natural host.
Autores: Vizcaino, N. ; Pérez Etayo, Lara; Conde Álvarez, Raquel; et al.
ISSN 0928-4249  Vol. 51  Nº 1  2020  págs. 101
Brucella ovisis a non-zoonotic roughBrucellathat causes genital lesions, abortions and increased perinatal mortality in sheep and is responsible for important economic losses worldwide. Research on virulence factors ofB. ovisis necessary for deciphering the mechanisms that enable this facultative intracellular pathogen to establish persistent infections and for developing a species-specific vaccine, a need in areas where the cross-protecting ovine smoothB. melitensisRev1 vaccine is banned. Although severalB. ovisvirulence factors have been identified, there is little information on its metabolic abilities and their role in virulence. Here, we report that deletion of pyruvate phosphate dikinase (PpdK, catalyzing the bidirectional conversion pyruvate -cc; phosphoenolpyruvate) inB. ovisPA (virulent and CO2-dependent) impaired growth in vitro. In cell infection experiments, although showing an initial survival higher than that of the parental strain, thisppdKmutant was unable to multiply. Moreover, when inoculated at high doses in mice, it displayed an initial spleen colonization higher than that of the parental strain followed by a marked comparative decrease, an unusual pattern of attenuation in mice. A homologous mutant was also obtained in aB. ovisPA CO2-independent construct previously proposed for developingB. ovisvaccines to solve the problem that CO2-dependence represents for large scale production. This CO2-independentppdKmutant reproduced the growth defect in vitro and the multiplication/clearance pattern in mouse spleens, and is thus an interesting vaccine candidate for the immunoprophylaxis ofB. ovisovine brucellosis.
Autores: Zabalza-Baranguá, A. ; San-Román, B. ; Chacón-Díaz, C. ; et al.
ISSN 1865-1674  Vol. 66  Nº 1  2019  págs. 505 - 516
Brucellosis is a worldwide zoonosis causing important economic loss and a public health problem. Small ruminants are the preferred hosts of Brucella melitensis and thus the main source of human infections. Effective control of sheep and goat brucellosis has been achieved in several countries through vaccination with the live-attenuated B. melitensis Rev1 vaccine. However, Rev1 induces a long-lasting serological response that hinders the differentiation between infected and vaccinated animals. A Rev1::gfp strain expressing constitutively the Green Fluorescent Protein (GFP) was built by stable insertion of a mini-Tn7-gfp in the glmS-recG non-codifying chromosomal region. An associated indirect ELISA-GFP was developed to identify anti-GFP antibodies in vaccinated animals. The resulting Rev1::gfp kept the biological properties of the Rev1 reference strain, including residual virulence and efficacy in mice, and was readily distinguished from Rev1 and other Brucella field strains by direct visualization under ultraviolet illumination, fluorescence microscopy and a multiplex PCR-GFP. The Rev1::gfp strain did not elicit anti-GFP antibodies itself in lambs but when applied in combination with recombinant GFP induced an intense and long-lasting (>9 months) anti-GFP serological response readily detectable by the ELISA-GFP. Overall, our results confirm that Rev1 GFP-tagging can be a suitable alternative for identifying vaccinated sheep in infected contexts.
Autores: Aragón Aranda, Beatriz; De Miguel, M.J.; Martínez Gómez, Estrella de Fátima; et al.
ISSN 1297-9716  Vol. 50  Nº 1  2019  págs. 95
Sheep brucellosis is a worldwide extended disease caused by B. melitensis and B. ovis, two species respectively carrying smooth or rough lipopolysaccharide. Vaccine B. melitensis Rev1 is used against B. melitensis and B. ovis but induces an anti-smooth-lipopolysaccharide response interfering with B. melitensis serodiagnosis, which precludes its use against B. ovis where B. melitensis is absent. In mice, Rev1 deleted in wbkC (Brucella lipopolysaccharide formyl-transferase) and carrying wbdR (E. coli acetyl-transferase) triggered antibodies that could be differentiated from those evoked by wild-type strains, was comparatively attenuated and protected against B. ovis, suggesting its potential as a B. ovis vaccine.
Autores: Barbier, T.; Zúñiga Ripa, Amaia; Moussa, S.; et al.
ISSN 1040-841X  Vol. 44  Nº 2  2018  págs. 182 - 211
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.
Autores: Conde Álvarez, Raquel; Palacios Chaves, Leyre; Gil Ramírez, Yolanda Teresa; et al.
ISSN 1664-302X  Vol. 8  2018 
The brucellae are facultative intracellular bacteria that cause a worldwide extended zoonosis. One of the pathogenicity mechanisms of these bacteria is their ability to avoid rapid recognition by innate immunity because of a reduction of the pathogen-associated molecular pattern (PAMP) of the lipopolysaccharide (LPS), free-lipids, and other envelope molecules. We investigated the Brucella homologs of lptA, lpxE, and lpxO, three genes that in some pathogens encode enzymes that mask the LPS PAMP by upsetting the core-lipid A charge/hydrophobic balance. Brucella lptA, which encodes a putative ethanolamine transferase, carries a frame-shift in B. abortus but not in other Brucella spp. and phylogenetic neighbors like the opportunistic pathogen Ochrobactrum anthropi. Consistent with the genomic evidence, a B. melitensis lptA mutant lacked lipid A-linked ethanolamine and displayed increased sensitivity to polymyxin B (a surrogate of innate immunity bactericidal peptides), while B. abortus carrying B. melitensis lptA displayed increased resistance. Brucella lpxE encodes a putative phosphatase acting on lipid A or on a free-lipid that is highly conserved in all brucellae and O. anthropi. Although we found no evidence of lipid A dephosphorylation, a B. abortus lpxE mutant showed increased polymyxin B sensitivity, suggesting the existence of a hitherto unidentified free-lipid involved in bactericidal peptide resistance. Gene lpxO putatively encoding an acyl hydroxylase carries a frame-shift in all brucellae except B. microti and is intact in O. anthropi. Free-lipid analysis revealed that lpxO corresponded to olsC, the gene coding for the ornithine lipid (OL) acyl hydroxylase active in O. anthropi and B. microti, while B. abortus carrying the olsC of O. anthropi and B. microti synthesized hydroxylated OLs. Interestingly, mutants in lptA, lpxE, or olsC were not attenuated in dendritic cells or mice. This lack of an obvious effect on virulence together with the presence of the intact homolog genes in O. anthropi and B. microti but not in other brucellae suggests that LptA, LpxE, or OL beta-hydroxylase do not significantly alter the PAMP properties of Brucella LPS and free-lipids and are therefore not positively selected during the adaptation to intracellular life.
Autores: Zúñiga Ripa, Amaia; Barbier, T.; Lázaro Antón, Leticia; et al.
ISSN 1664-302X  Vol. 9  2018  págs. 641
Bacteria of the genus Brucella infect a range of vertebrates causing a worldwide extended zoonosis. The best-characterized brucellae infect domestic livestock, behaving as stealthy facultative intracellular parasites. This stealthiness depends on envelope molecules with reduced pathogen-associated molecular patterns, as revealed by the low lethality and ability to persist in mice of these bacteria. Infected cells are often engorged with brucellae without signs of distress, suggesting that stealthiness could also reflect an adaptation of the parasite metabolism to use local nutrients without harming the cell. To investigate this, we compared key metabolic abilities of Brucella abortus 2308 Wisconsin (2308W), a cattle biovar 1 virulent strain, and B. suis 513, the reference strain of the ancestral biovar 5 found in wild rodents. B. suis 513 used a larger number of C substrates and showed faster growth rates in vitro, two features similar to those of B. microti, a species phylogenomically close to B. suis biovar 5 that infects voles. However, whereas B. microti shows enhanced lethality and reduced persistence in mice, B. suis 513 was similar to B. abortus 2308W in this regard. Mutant analyses showed that B. suis 513 and B. abortus 2308W were similar in that both depend on phosphoenolpyruvate synthesis for virulence but not on the classical gluconeogenic fructose-1,6-bisphosphatases Fbp-GlpX or on isocitrate lyase (AceA). However, B. suis 513 used pyruvate phosphate dikinase (PpdK) and phosphoenolpyruvate carboxykinase (PckA) for phosphoenolpyruvate synthesis in vitro while B. abortus 2308W used only PpdK. Moreover, whereas PpdK dysfunction causes attenuation of B. abortus 2308W in mice, in B. suis, 513 attenuation occurred only in the double PckA-PpdK mutant. Also contrary to what occurs in B. abortus 2308, a B. suis 513 malic enzyme (Mae) mutant was not attenuated, and this independence of Mae and the role of PpdK was confirmed by the lack of attenuation of a double Mae-PckA mutant. Altogether, these results decouple fast growth rates from enhanced mouse lethality in the brucellae and suggest that an Fbp-GlpX-independent gluconeogenic mechanism is ancestral in this group and show differences in central C metabolic steps that may reflect a progressive adaptation to intracellular growth.
Autores: Pérez Etayo, Lara; de Miguel, M. J.; Conde Álvarez, Raquel; et al.
ISSN 1297-9716  Vol. 49  Nº 1  2018  págs. 85
Brucella bacteria cause brucellosis, a major zoonosis whose control requires efficient diagnosis and vaccines. Identification of classical Brucella spp. has traditionally relied on phenotypic characterization, including surface antigens and 5-10% CO2 necessity for growth (CO2-dependence), a trait of Brucella ovis and most Brucella abortus biovars 1-4 strains. Although molecular tests are replacing phenotypic methods, CO2-dependence remains of interest as it conditions isolation and propagation and reflects Brucella metabolism, an area of active research. Here, we investigated the connection of CO2-dependence and carbonic anhydrases (CA), the enzymes catalyzing the hydration of CO2 to the bicarbonate used by anaplerotic and biosynthetic carboxylases. Based on the previous demonstration that B. suis carries two functional CAs (CAI and CAII), we analyzed the CA sequences of CO2-dependent and -independent brucellae and spontaneous mutants. The comparisons strongly suggested that CAII is not functional in CO2-dependent B. abortus and B. ovis, and that a modified CAII sequence explains the CO2-independent phenotype of spontaneous mutants. Then, by mutagenesis and heterologous plasmid complementation and chromosomal insertion we proved that CAI alone is enough to support CO2-independent growth of B. suis in rich media but not of B. abortus in rich media or B. suis in minimal media.
Autores: Salvador Bescós, Miriam; Gil Ramírez, Yolanda Teresa; Zúñiga Ripa, Amaia; et al.
ISSN 1664-302X  Vol. 9  Nº 2293  2018 
Brucellosis, an infectious disease caused by Brucella, is one of the most extended bacterial zoonosis in the world and an important cause of economic losses and human suffering. The lipopolysaccharide (LPS) of Brucella plays a major role in virulence as it impairs normal recognition by the innate immune system and delays the immune response. The LPS core is a branched structure involved in resistance to complement and polycationic peptides, and mutants in glycosyltransferases required for the synthesis of the lateral branch not linked to the O-polysaccharide (O-PS) are attenuated and have been proposed as vaccine candidates. For this reason, the complete understanding of the genes involved in the synthesis of this LPS section is of particular interest. The chemical structure of the Brucella LPS core suggests that, in addition to the already identified WadB and WadC glycosyltransferases, others could be implicated in the synthesis of this lateral branch. To clarify this point, we identified and constructed mutants in 11 ORFs encoding putative glycosyltransferases in B. abortus. Four of these ORFs, regulated by the virulence regulator MucR (involved in LPS synthesis) or the BvrR/BvrS system (implicated in the synthesis of surface components), were not required for the synthesis of a complete LPS neither for virulence or interaction with polycationic peptides and/or complement. Among the other seven ORFs, six seemed not to be required for the synthesis of the core LPS since the corresponding mutants kept the O-PS and reacted as the wild type with polyclonal sera. Interestingly, mutant in ORF BAB1_0953 (renamed wadD) lost reactivity against antibodies that recognize the core section while kept the O-PS. This suggests that WadD is a new glycosyltransferase adding one or more sugars to the core lateral branch. WadD mutants were more sensitive than the parental strain to components of the innate immune system and played a role in chronic stages of infection. These results corroborate and extend previous work indicating that the Brucella LPS core is a branched structure that constitutes a steric impairment preventing the elements of the innate immune system to fight against Brucella
Autores: Martínez Gómez, Estrella de Fátima; Stahle, J.; Gil Ramírez, Yolanda Teresa; et al.
ISSN 1664-302X  Vol. 9  2018  págs. 1092
Brucellosis is a bacterial zoonosis of worldwide distribution caused by bacteria of the genus Brucella. In Brucella abortus and Brucella melitensis, the major species infecting domestic ruminants, the smooth lipopolysaccharide (S-LPS) is a virulence factor. This S-LPS carries a N-formyl-perosamine homopolymer O-polysaccharide that is the major antigen in serodiagnostic tests and is required for virulence. We report that the Brucella O-PS can be structurally and antigenically modified using wbdR, the acetyl-transferase gene involved in N-acetyl-perosamine synthesis in Escherichia coli O157:H7. Brucella constructs carrying plasmidic wbdR expressed a modified O-polysaccharide but were unstable, a problem circumvented by inserting wbdR into a neutral site of chromosome II. As compared to wild-type bacteria, both kinds of wbdR constructs expressed shorter O-polysaccharides and NMR analyses showed that they contained both N-formyl and N-acetyl-perosamine. Moreover, deletion of the Brucella formyltransferase gene wbkC in wbdR constructs generated bacteria producing only N-acetyl-perosamine homopolymers, proving that wbdR can replace for wbkC. Absorption experiments with immune sera revealed that the wbdR constructs triggered antibodies to new immunogenic epitope(s) and the use of monoclonal antibodies proved that B. abortus and B. melitensis wbdR constructs respectively lacked the A or M epitopes, and the absence of the C epitope in both backgrounds. The wbdR constructs showed resistance to polycations similar to that of the wild-type strains but displayed increased sensitivity to normal serum similar to that of a per R mutant. In mice, the wbdR constructs produced chronic infections and triggered antibody responses that can be differentiated from those evoked by the wild-type strain in S-LPS ELISAs. These results open the possibilities of developing brucellosis vaccines that are both antigenically tagged and lack the diagnostic epitopes of virulent field strains, thereby solving the diagnostic interference created by current vaccines against Brucella.
Autores: Fontana, C.; Conde Álvarez, Raquel; Ståhle, J.; et al.
ISSN 0021-9258  Vol. 291  Nº 14  2016  págs. 7727 - 7741
The structures of the lipooligosaccharides from Brucella melitensis mutants affected in the WbkD and ManB(core) proteins have been fully characterized using NMR spectroscopy. The results revealed that disruption of wbkD gives rise to a rough lipopolysaccharide (R-LPS) with a complete core structure (beta-D-Glcp-(1 -> 4)-alpha-Kdop-(2 -> 4)[beta-D-GlcpN-(1 -> 6)-beta-D-GlcpN-(1 -> 4)[beta-D-GlcpN-(1 -> 6)]-beta-D-GlcpN-(1 -> 3)-alpha-D-Manp-(1 -> 5)]-alpha-Kdop-(2 -> 6)-beta-D-GlcpN3N4P-(1 -> 6)-alpha-D-GlcpN3N1P), in addition to components lacking one of the terminal beta-D-GlcpN and/or the beta-D-Glcp residues (48 and 17%, respectively). These structures were identical to those of the R-LPS from B. melitensis EP, a strain simultaneously expressing both smooth and R-LPS, also studied herein. In contrast, disruption of man-B-core gives rise to a deep-rough pentasaccharide core (beta-D-Glcp-(1 -> 4)-alpha-Kdop-(2 -> 4)-alpha-Kdop-(2 -> 6)-beta-D-GlcpN3N4P-(1 -> 6)-alpha-D-GlcpN3N1P) as the major component (63%), as well as a minor tetrasaccharide component lacking the terminal beta-D-Glcp residue (37%). These results are in agreement with the predicted functions of the WbkD (glycosyltransferase involved in the biosynthesis of the O-antigen) and ManB(core) proteins (phosphomannomutase involved in the biosynthesis of a mannosyl precursor needed for the biosynthesis of the core and O-antigen). We also report that deletion of B. melitensis wadC removes the core oligosaccharide branch not linked to the O-antigen causing an increase in overall negative charge of the remaining LPS inner section. This is in agreement with the mannosyltransferase role predicted for WadC and the lack of GlcpN residues in the defective core oligosaccharide. Despite carrying the O-antigen essential in B. melitensis virulence, the core deficiency in the wadC mutant structure resulted in a more efficient detection by innate immunity and attenuation, proving the role of the beta-D-GlcpN-(1 -> 6)-beta-D-GlcpN-(1 -> 4)[beta-D-GlcpN-(1 -> 6)]-beta-D-GlcpN-(1 -> 3)-alpha-D-Manp-(1 -> 5) structure in virulence.
Autores: Soler Llorens, Pedro Francisco; Gil Ramírez, Yolanda Teresa; Zabalza Baranguá, Ana; et al.
ISSN 0928-4249  Vol. 45  Nº 72  2014 
Brucella spp. are Gram-negative bacteria that behave as facultative intracellular parasites of a variety of mammals. This genus includes smooth (S) and rough (R) species that carry S and R lipopolysaccharides (LPS), respectively. S-LPS is a virulence factor, and mutants affected in the S-LPS O-polysaccharide (R mutants), core oligosaccharide or both show attenuation. However, B. ovis is naturally R and is virulent in sheep. We studied the role of B. ovis LPS in virulence by mutating the orthologues of wadA, wadB and wadC, three genes known to encode LPS core glycosyltransferases in S brucellae. When mapped with antibodies to outer membrane proteins (Omps) and R-LPS, wadB and wadC mutants displayed defects in LPS structure and outer membrane topology but inactivation of wadA had little or no effect. Consistent with these observations, the wadB and wadC but not the wadA mutants were attenuated in mice. When tested as vaccines, the wadB and wadC mutants protected mice against B. ovis challenge. The results demonstrate that the LPS core is a structure essential for survival in vivo not only of S brucellae but also of a naturally R Brucella pathogenic species, and they confirm our previous hypothesis that the Brucella LPS core is a target for vaccine development. Since vaccine B. melitensis Rev 1 is S and thus interferes in serological testing for S brucellae, wadB mutant represents a candidate vaccine to be evaluated against B. ovis infection of sheep suitable for areas free of B. melitensis.
Autores: Gil Ramírez, Yolanda Teresa; Conde Álvarez, Raquel; Palacios Chaves, Leyre; et al.
ISSN 0882-4010  Vol. 73  2014  págs. 53 - 59
Brucellosis is a worldwide extended zoonosis caused by Brucella spp. These gram-negative bacteria are not readily detected by innate immunity, a virulence-related property largely linked to their surface lipopolysaccharide (LPS). The role of the LPS lipid A and O-polysaccharide in virulence is well known. Moreover, mutation of the glycosyltransferase gene wadC of Brucella abortus, although not affecting O-polysaccharide assembly onto the lipid-A core section causes a core oligosaccharide defect that increases recognition by innate immunity. Here, we report on a second gene (wadB) encoding a LPS core glycosyltransferase not involved in the assembly of the O-polysaccharide-linked core section. As compared to wild-type B. abortus, a wadB mutant was sensitive to bactericidal peptides and non-immune serum, and was attenuated in mice and dendritic cells. These observations show that as WadC, WadB is also involved in the assembly of a branch of Brucella LPS core and support the concept that this LPS section is a virulence-related structure.
Autores: Zúñiga Ripa, Amaia; Barbier, Thilbault ; Conde Álvarez, Raquel; et al.
ISSN 0021-9193  Vol. 196  Nº 16  2014  págs. 3045 - 3057
The brucellae are the etiological agents of brucellosis, a worldwide-distributed zoonosis. These bacteria are facultative intracellular parasites and thus are able to adjust their metabolism to the extra- and intracellular environments encountered during an infectious cycle. However, this aspect of Brucella biology is imperfectly understood, and the nutrients available in the intracellular niche are unknown. Here, we investigated the central pathways of C metabolism used by Brucella abortus by deleting the putative fructose-1,6-bisphosphatase (fbp and glpX), phosphoenolpyruvate carboxykinase (pckA), pyruvate phosphate dikinase (ppdK), and malic enzyme (mae) genes. In gluconeogenic but not in rich media, growth of ¿ppdK and ¿mae mutants was severely impaired and growth of the double ¿fbp-¿glpX mutant was reduced. In macrophages, only the ¿ppdK and ¿mae mutants showed reduced multiplication, and studies with the ¿ppdK mutant confirmed that it reached the replicative niche. Similarly, only the ¿ppdK and ¿mae mutants were attenuated in mice, the former being cleared by week 10 and the latter persisting longer than 12 weeks. We also investigated the glyoxylate cycle. Although aceA (isocitrate lyase) promoter activity was enhanced in rich medium, aceA disruption had no effect in vitro or on multiplication in macrophages or mouse spleens. The results suggest that B. abortus grows intracellularly using a limited supply of 6-C (and 5-C) sugars that is compensated by glutamate and possibly other amino acids entering the Krebs cycle without a critical role of the glyoxylate shunt.
Autores: Zaccheus, Mona V.; Ali, Tara; Cloeckaert, Axel; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 8  Nº 1  2013  págs. e53941
The brucellae are Gram-negative bacteria that cause an important zoonosis. Studies with the main Brucella species have shown that the O-antigens of the Brucella smooth lipopolysaccharide are alpha-(1 -> 2) and alpha-(1 -> 3)-linked N-formyl-perosamine polysaccharides that carry M, A and C (A = M, A>M and A<M) epitopes relevant in serodiagnosis and typing. We report that, in contrast to the B. suis biovar 1 O-antigen used as a reference or to all described Brucella O-antigens, B. suis biovar 2 O-antigen failed to bind monoclonal antibodies of C (A = M), C (M>A) and M specificities. However, the biovar 2 O-antigen bound monoclonal antibodies to the Brucella A epitope, and to the C/Y epitope shared by brucellae and Yersinia enterocolitica O:9, a bacterium that carries an N-formyl-perosamine O-antigen in exclusively alpha-(1 -> 2)-linkages. By C-13 NMR spectroscopy, B. suis biovar 1 but not B. suis biovar 2 or Y.enterocolitica O:9 polysaccharide showed the signal characteristic of alpha-(1 -> 3)-linked N-formyl-perosamine, indicating that biovar 2 may altogether lack this linkage. Taken together, the NMR spectroscopy and monoclonal antibody analyses strongly suggest a role for alpha-(1 -> 3)-linked N-formyl-perosamine in the C (A = M) and C (M>A) epitopes. Moreover, they indicate that B. suis biovar 2 O-antigen lacks some lipopolysaccharide epitopes previously thought to be present in all smooth brucellae, thus representing a new brucella serovar that is M-negative, C-negative. Serologically and structurally this new serovar is more similar to Y. enterocolitica O:9 than to other brucellae.
Autores: Conde Álvarez, Raquel; Arce-Gorvel, Vilma; Gil-Ramírez, Yolanda; et al.
ISSN 0882-4010  Vol. 58  2013  págs. 29-34
The gram-negative bacteria of the genus Brucella are facultative intracellular parasites that cause brucellosis, a world wide-distributed zoonotic disease that represents a serious problem for animal and human health. There is no human-to-human contagion and, since there is no human vaccine, animal vaccination is essential to control brucellosis. However, current vaccines (all developed empirically) do not provide 100% protection and are infectious in humans. Attempts to generate new vaccines by obtaining mutants lacking the lipopolysaccharide O-polysaccharide, in purine metabolism or in Brucella type IV secretion system have not been successful. Here we propose a new approach to develop brucellosis vaccines based on the concept that Brucella surface molecules evade efficient detection by innate immunity, thus delaying protective Th1 responses and opening a time window to reach sheltered intracellular compartments. We showed recently that a branch of the core oligosaccharide section of Brucella lipopolysaccharide hampers recognition by TLR4-MD2. Mutation of glycosyltransferase WadC, involved in the synthesis of this branch, results in a lipopolysaccharide that, while keeping the O-polysaccharide essential for optimal protection, shows a truncated core, is more efficiently recognized by MD2 and triggers an increased cytokine response. In keeping with this, the wadC mutant is attenuated in dendritic cells and mice. In the mouse model of brucellosis vaccines, the Brucella abortus wadC mutant conferred protection similar to that provided by S19, the best cattle vaccine available. The properties of the wadC mutant provide the proof of concept for this new approach and open the way for more effective brucellosis vaccines.
Autores: Palacios Chaves, Leyre; Conde Álvarez, Raquel; Zúñiga Ripa, Amaia; et al.
ISSN 0175-7571  Vol. 42  Nº Supl. 1  2013  págs. S154
Autores: Conde Álvarez, Raquel; Arce - Gorvel, V.; Iriarte Cilveti, Maite; et al.
ISSN 1553-7374  Vol. 8  Nº 5  2012  págs. e1002675
Innate immunity recognizes bacterial molecules bearing pathogen-associated molecular patterns to launch inflammatory responses leading to the activation of adaptive immunity. However, the lipopolysaccharide (LPS) of the gram-negative bacterium Brucella lacks a marked pathogen-associated molecular pattern, and it has been postulated that this delays the development of immunity, creating a gap that is critical for the bacterium to reach the intracellular replicative niche. We found that a B. abortus mutant in the wadC gene displayed a disrupted LPS core while keeping both the LPS O-polysaccharide and lipid A. In mice, the wadC mutant induced proinflammatory responses and was attenuated. In addition, it was sensitive to killing by non-immune serum and bactericidal peptides and did not multiply in dendritic cells being targeted to lysosomal compartments. In contrast to wild type B. abortus, the wadC mutant induced dendritic cell maturation and secretion of pro-inflammatory cytokines. All these properties were reproduced by the wadC mutant purified LPS in a TLR4-dependent manner. Moreover, the core-mutated LPS displayed an increased binding to MD-2, the TLR4 co-receptor leading to subsequent increase in intracellular signaling. Here we show that Brucella escapes recognition in early stages of infection by expressing a shield against recognition by innate immunity in its LPS core and identify a novel virulence mechanism in intracellular pathogenic gram-negative bacteria. These results also encourage for an improvement in the generation of novel bacterial vaccines.
Autores: Palacios Chaves, Leyre; Zúñiga Ripa, Amaia; Gutiérrez, A.; et al.
ISSN 1350-0872  Vol. 158  Nº 4  2012  págs. 1037 - 1044
The brucellae are facultative intracellular pathogens of mammals that are transmitted by contact with infected animals or contaminated materials. Several major lipidic components of the brucella cell envelope are imperfectly recognized by innate immunity, thus contributing to virulence. These components carry large proportions of acyl chains of lactobacillic acid, a long chain cyclopropane fatty acid (CFA). CFAs result from addition of a methylene group to unsaturated acyl chains and contribute to resistance to acidity, dryness and high osmolarity in many bacteria and to virulence in mycobacteria. We examined the role of lactobacillic acid in Brucella abortus virulence by creating a mutant in ORF BAB1_0476, the putative CFA synthase gene. The mutant did not incorporate [(14)C]methyl groups into lipids, lacked CFAs and synthesized the unsaturated precursors, proving that BAB1_0476 actually encodes a CFA synthase. BAB1_0476 promoter-luxAB fusion studies showed that CFA synthase expression was promoted by acid pH and high osmolarity. The mutant was not attenuated in macrophages or mice, strongly suggesting that CFAs are not essential for B. abortus intracellular life. However, when the mutant was tested under high osmolarity on agar and acid pH, two conditions likely to occur on contaminated materials and fomites, they showed reduced ability to grow or survive. Since CFA synthesis entails high ATP expenses and brucellae produce large proportions of lactobacillic acyl chains, we speculate that the CFA synthase has been conserved because it is useful for survival extracellularly, thus facilitating persistence in contaminated materials and transmission to new hosts.
Autores: Palacios Chaves, Leyre; Conde Álvarez, Raquel; Gil Ramírez, Yolanda Teresa; et al.
ISSN 1438-4221  Vol. 302  Nº Supl. 1  2012  págs. 79
Autores: Palacios Chaves, Leyre; Conde Álvarez, Raquel; Gil Ramírez, Yolanda Teresa; et al.
Revista: PLoS One
ISSN 1932-6203  Vol. 6  Nº 1  2011  págs. e16030
The brucellae are ¿-Proteobacteria facultative intracellular parasites that cause an important zoonosis. These bacteria escape early detection by innate immunity, an ability associated to the absence of marked pathogen-associated molecular patterns in the cell envelope lipopolysaccharide, lipoproteins and flagellin. We show here that, in contrast to the outer membrane ornithine lipids (OL) of other Gram negative bacteria, Brucella abortus OL lack a marked pathogen-associated molecular pattern activity. We identified two OL genes (olsB and olsA) and by generating the corresponding mutants found that olsB deficient B. abortus did not synthesize OL or their lyso-OL precursors. Liposomes constructed with B. abortus OL did not trigger IL-6 or TNF-¿ release by macrophages whereas those constructed with Bordetella pertussis OL and the olsB mutant lipids as carriers were highly active. The OL deficiency in the olsB mutant did not promote proinflammatory responses or generated attenuation in mice. In addition, OL deficiency did not increase sensitivity to polymyxins, normal serum or complement consumption, or alter the permeability to antibiotics and dyes. Taken together, these observations indicate that OL have become dispensable in the extant brucellae and are consistent within the trend observed in ¿-Proteobacteria animal pathogens to reduce and eventually eliminate the envelope components susceptible of recognition by innate immunity.