Showing papers by "Jean-Pierre Gorvel published in 2009"

The glyceraldehyde-3-phosphate dehydrogenase and the small GTPase Rab 2 are crucial for Brucella replication.

Abstract: The intracellular pathogen Brucella abortus survives and replicates inside host cells within an endoplasmic reticulum (ER)-derived replicative organelle named the "Brucella-containing vacuole" (BCV). Here, we developed a subcellular fractionation method to isolate BCVs and characterize for the first time the protein composition of its replicative niche. After identification of BCV membrane proteins by 2 dimensional (2D) gel electrophoresis and mass spectrometry, we focused on two eukaryotic proteins: the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the small GTPase Rab 2 recruited to the vacuolar membrane of Brucella. These proteins were previously described to localize on vesicular and tubular clusters (VTC) and to regulate the VTC membrane traffic between the endoplasmic reticulum (ER) and the Golgi. Inhibition of either GAPDH or Rab 2 expression by small interfering RNA strongly inhibited B. abortus replication. Consistent with this result, inhibition of other partners of GAPDH and Rab 2, such as COPI and PKC iota, reduced B. abortus replication. Furthermore, blockage of Rab 2 GTPase in a GDP-locked form also inhibited B. abortus replication. Bacteria did not fuse with the ER and instead remained in lysosomal-associated membrane vacuoles. These results reveal an essential role for GAPDH and the small GTPase Rab 2 in B. abortus virulence within host cells.

The Differential Interaction of Brucella and Ochrobactrum with Innate Immunity Reveals Traits Related to the Evolution of Stealthy Pathogens

Abstract: Background During evolution, innate immunity has been tuned to recognize pathogen-associated molecular patterns. However, some α-Proteobacteria are stealthy intracellular pathogens not readily detected by this system. Brucella members follow this strategy and are highly virulent, but other Brucellaceae like Ochrobactrum are rhizosphere inhabitants and only opportunistic pathogens. To gain insight into the emergence of the stealthy strategy, we compared these two phylogenetically close but biologically divergent bacteria.

Is Brucella an enteric pathogen

Abstract: Below, we comment on the article by Renée M. Tsolis, Glenn M. Young, Jay V. Solnick and Andreas J. Bäumler (Exit strategies of intracellular pathogens. Nature Rev. Microbiol. 6, 883–892 (2008))1. As suggested previously2, the authors propose that the stealthy strategy and cognate reduction in pathogen-associated molecular patterns (PAMPs) of envelope molecules are crucial to Brucella pathogenicity. Although we agree with this view, we feel that the article overemphasizes the parallels with Salmonella enterica subsp. enterica serovar Typhi. Both pathogens invade the lymphatic system and proliferate within regional lymph nodes, but Brucella cannot be grouped with enteric pathogens. It is doubtful that primary invasion after Brucella ingestion occurs through the intestine. Indeed, dairy products are a source of contagion but solid epidemiological evidence and studies in volunteers have shown that ingestion is inefficient compared with other routes (for example, skin abrasions and aerosols)3. Moreover, although Brucella is markedly sensitive to gastric juice, no relationship between achlorhydria and brucellosis has been observed3, indicating that mucosae are not regularly penetrated beyond the oropharynx. Importantly, brucellae can be isolated from tonsils, there is regional lymphadenitis and constipation is far more common than diarrhoea3,4. In cattle, colonization of the lymph nodes that drain the face area is about as frequent in natural infection as in artificial conjunctival infections5. All these observations indicate that the upper mucosae are the normal site of entry, which is consistent with the formidable ecophysiological challenge that the rumen and the intestine pose to brucellae. Whereas Salmonella envelopes are effective barriers that allow growth in the presence of bile salts, Brucella envelopes are permeable to hydrophobic compounds. This is not a coincidence, because the reduction of Brucella lipopolysaccharide PAMPs2,6 (which is essential in the stealthy strategy) is connected to loss of the barrier7. It is true that when ligated ileal loops of calves are experimentally injected with large amounts of Brucella, the bacteria penetrate through lymphoepithelial M-like cells8. However, this probably reflects the use of this model and of large amounts of brucellae, rather than the outcome of an oral infection. Clinically, there is no intestinal damage in brucellosis, whereas necrosis of Peyer’s patches is common in untreated typhoid fever. That Brucella is not an enteric pathogen is also supported by phylogenetic and cellular studies. The brucellae belong to the Alphaproteobacteria9, together with Bartonella, Anaplasma, Ehrlichia and Rickettsia, all of which are intracellular pathogens and share common themes of pathobiology10. For example, fever is not manifested in concordance with proinflammatory acute responses triggered by PAMP-bearing molecules2,6,11, as occurs in typhoid fever, but rather as a consequence of adaptive immunity and, in some cases, hypersensitivity. In addition, Salmonella spp. use at least two type III secretion systems that are encoded in pathogenicity islands (Salmonella pathogenicity islands 1 and 2)12 whereas, consistent with its phylogeny, brucellae rely on a type IV secretion system (VirB) for intracellular survival and replication13. Recently, one of our laboratories has reported that Brucella Btp1 interferes with the Toll-like receptor 2 signalling pathway, suggesting that Brucella and Salmonella share some mechanisms of immune evasion14. However, the marked structural, physiological and phylogenetic differences between these two bacteria are fundamental features that set a clear distinction in their pathobiology.

Brucella, a Perfect Trojan Horse in Phagocytes

Abstract: Several species of the genus Brucella are responsible for brucellosis: Brucella melitensis, B. abortus, B. suis, B. canis, B. ovis, and B. neotomae. Brucella has also been isolated from a variety of terrestrial wildlife mammal species such as elk, buffalo, reindeer, and bison as well as from marine mammals, illustrating its broad host range. Currently, of the six main species of Brucella, four can cause disease in humans, with B. melitensis having the most severe pathogenicity, followed by B. suis, which is more rare but still presents severe pathogenicity, and then B. abortus and B. canis, which are less pathogenic in humans. Significant progress has been made in our understanding of the virulence factors that enable Brucella to reside within phagocytic cells and escape their killing mechanisms. In essence, Brucella is able to proliferate extensively within both macrophages and nonphagocytic epithelial cells without affecting their basic cellular functions or inducing cell death. It efficiently controls its own intracellular trafficking in order to avoid degradation within lysosomes and reach an intracellular compartment suited for replication, which we commonly designate as the Brucella-containing vacuole (BCV). Several virulence factors have been implicated in Brucella resistance to cellular defensive mechanisms and interaction with cellular pathways to create the environment suited for its intracellular survival. In recent years great advances have been made in our understanding of its pathogenesis, due in particular to the availability of the genome sequences.