Nathalie Pradel

Aix-Marseille Université, Marsiglia, Provence-Alpes-Côte d'Azur, France

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Publications (49)126.06 Total impact

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    ABSTRACT: Multicellular magnetotactic prokaryotes (MMPs) are a peculiar group of magnetotactic bacteria, each comprising approximately 10-100 cells of the same phylotype. Two morphotypes of MMP have been identified, including several species of globally distributed spherical mulberry-like MMPs (s-MMPs), and two species of ellipsoidal pineapple-like MMPs (e-MMPs) from China (Qingdao and Rongcheng cities). We recently collected e-MMPs from Mediterranean Sea sediments (Six-Fours-les-Plages) and Drummond Island, in the South China Sea. Phylogenetic analysis revealed that the MMPs from Six-Fours-les-Plages and the previously reported e-MMP Candidatus Magnetananas rongchenensis have 98.5% sequence similarity and are the same species, while the MMPs from Drummond Island appear to be a novel species, having > 7.1% sequence divergence from the most closely related e-MMP, Candidatus Magnetananas tsingtaoensis. Identification of the novel species expands the distribution of e-MMPs to Tropical Zone. Comparison of nine physical and chemical parameters revealed that sand grain size and the content of inorganic nitrogen (nitrate, ammonium and nitrite) in the sediments from Rongcheng City and Six-Fours-les-Plages were similar, and lower than found for sediments from the other two sampling sites. The results of the study reveal broad diversity and wide distribution of e-MMPs.
    Full-text · Article · Dec 2015 · Environmental Microbiology Reports
  • Nathalie Pradel · Maxime Fuduche · Bernard Ollivier
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    ABSTRACT: In this study, we report for the first time the presence of magnetotactic bacteria (MTB) on the Northeastern Atlantic coast. Microscopy observations indicated a heterogeneous population of MTB morphotypes. The analysis of the 16S rDNA by pyrosequencing technology revealed four operational taxonomic sequence units affiliated within the Magnetococcales order, class Alphaproteobacteria. One of them was closely related to sequences of MTB from the Tunisian coast, central Mediterranean Sea. This work offers information on anew environmental context and on biogeography of MTB, highlights the putative impact that marine currents may have on MTB distribution on Earth, and underlines the role that pristine or polluted areas may play on the structure of the MTB communites.
    No preview · Article · Sep 2015 · Environmental Science and Pollution Research
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    ABSTRACT: A novel, anaerobic, chemoorganotrophic bacterium, designated strain Ra1766HT, was isolated from sediments of the Guaymas basin (Gulf of California, Mexico) at 2002 m depth. Cells were thin, motile, Gram-positive flexible rods forming terminal endospores. Strain Ra1766HT grew at temperatures between 25-45 °C (optimum 30 °C), pH 6.7-8.1 (optimum 7.5) and salinity between 5-60 g/L (optimum 30 g/L). It was an obligate heterotrophic bacterium fermenting carbohydrates (glucose and mannose) and organic acids (pyruvate, succinate). Casamino acids and amino acids (glutamate, aspartate and glycine) were also fermented. The main end-products from glucose fermentation were acetate, butyrate, ethanol, H2 and CO2. Sulfate, sulfite, thiosulfate, elemental sulfur, fumarate, nitrate, nitrite and Fe(III) were not used as terminal electron acceptors. The predominant cellular fatty acids were C14:0 C16:1 ω7, C16:1 ω7 DMA and C16: The main polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, and phospholipids. The G + C % content of the genomic DNA was 33.7 %. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain Ra1766HT was affiliated to the bacterial cluster XI of the order Clostridiales, phylum Firmicutes. The closest phylogenetic relative of Ra1766HT was Geosporobacter subterraneus (94.2 % similarity). On the basis of phylogenetic inference and phenotypic properties, strain Ra1766HT (= DSM 27501T = JCM 19377T) is proposed as the type strain of a novel species of a novel genus, Crassaminicella profunda.
    No preview · Article · Jun 2015 · International Journal of Systematic and Evolutionary Microbiology
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    ABSTRACT: The occurrence of magnetotactic bacteria (MTB) on a Tunisian marine coast exposed to heavy metals pollution (Sfax, Gulf of Gabès, Mediterranean Sea) was investigated. The MTB population of this Southern Mediterranean coast was compared to the MTB populations previously investigated on the French Northern Mediterranean coast. A dominant MTB coccus morphotype was observed by microscopy analysis. By pyrosequencing technology, the analysis of the 16S ribosomal RNA (rDNA) revealed as much as 33 operational taxonomic sequence units (OTUs) close to sequences of MTB accessible in the databases. The majority were close to MTB sequences of the "Med group" of α-Proteobacteria. Among them, a dominant OTU_001 (99 % of the MTB sequences) affiliated within the Magnetococcales order was highlighted. Investigating the capacities of this novel bacterium to be used in bioremediation and/or depollution processes could be envisaged.
    No preview · Article · Mar 2015 · Environmental Science and Pollution Research
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    ABSTRACT: Shiga toxin-producing Escherichia coli (STEC) are able to cause serious illnesses ranging from diarrhea to hemorrhagic colitis and hemolytic-uremic syndrome (HUS). These bacteria colonize the digestive tract of humans and produce Shiga-toxins, which are considered to be essential for virulence and are crucial in lethal infection. Colon colonization is supposed to be a determinant step in the development of the infection, but the virulence traits that mediate this step are unclear. We analyzed the ability of 256 STEC strains belonging to seropathotype A (the most virulent O157:H7 serotype) to seropathotype E (not involved in human disease) to adhere to HEp-2, HCT-8, and T84 cell lines. Of the 256 STEC tested most (82%) were non-adherent in our assays. The adhesion levels were globally low and were not related to pathogenicity, although the highest levels were associated to O26:H11 and O103:H2 strains of seropathotype B (associated with HUS but less commonly than serotype O157:H7), possessing both the eae and toxB genes.
    Full-text · Article · Feb 2015 · Frontiers in Microbiology
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    ABSTRACT: Magnetotactic bacteria synthesize intracellular magnetite and/or greigite magnetosome crystals. They play a significant role in both iron and sulfur cycles in sedimentary aquatic environments. To get insight into the bio-geochemical contribution of MTB, more studies concerning their ecology and their distribution in diverse habitats are necessary. The MTB community of an oil-industry polluted area of the French Mediterranean coast has been previously investigated. Here, we investigate the MTB community from coastal sediments of a Mediterranean pristine area using optical and transmission electron microscopy and phylogenetic analysis based on 16S rRNA gene sequences. A particularly high diversity of MTB was observed, with cocci phylogenetically distributed across the order Magnetococcales, including a novel cluster with sequences from the Mediterranean Sea designated as “Med group”, and novel morphotypes.
    No preview · Article · Dec 2014 · Current Microbiology
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    ABSTRACT: RNA-seq was used to study the response of Desulfovibrio hydrothermalis, isolated from a deep-sea hydrothermal chimney on the East-Pacific Rise at a depth of 2,600 m, to various hydrostatic pressure growth conditions. The transcriptomic datasets obtained after growth at 26, 10 and 0.1 MPa identified only 65 differentially expressed genes that were distributed among four main categories: aromatic amino acid and glutamate metabolisms, energy metabolism, signal transduction, and unknown function. The gene expression patterns suggest that D. hydrothermalis uses at least three different adaptation mechanisms, according to a hydrostatic pressure threshold (HPt) that was estimated to be above 10 MPa. Both glutamate and energy metabolism were found to play crucial roles in these mechanisms. Quantitation of the glutamate levels in cells revealed its accumulation at high hydrostatic pressure, suggesting its role as a piezolyte. ATP measurements showed that the energy metabolism of this bacterium is optimized for deep-sea life conditions. This study provides new insights into the molecular mechanisms linked to hydrostatic pressure adaptation in sulfate-reducing bacteria.
    Full-text · Article · Sep 2014 · PLoS ONE
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    ABSTRACT: Bacteria of the genus Photobacterium thrive worldwide in oceans and show substantially varied lifestyles, including free-living, commensal, pathogenic, symbiotic, and piezophilic. Here, we present the genome sequence of a luminous, piezophilic Photobacterium phosphoreum strain, ANT-2200, isolated from a water column at 2,200 m depth in the Mediterranean Sea. It is the first genomic sequence of the P. phosphoreum group. An analysis of the sequence provides insight into the adaptation of bacteria to the deep-sea habitat.
    Full-text · Article · Mar 2014 · Genome Announcements
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    ABSTRACT: A novel obligately anaerobic, non-spore-forming, rod-shaped mesophilic, halophilic, Gram-stain-negative bacterium, was isolated from sediments of Guaymas Basin. The strain, designated Ra1766G1(T), grew at 20-40 degrees C (optimum, 30-35 degrees C) and at pH 6.0-8.0 (optimum, pH 6.5-7.5). It required 0.5-7.5 % NaCl (optimum, 2-3 %) for growth. Sulfate, thiosulfate, elemental sulfur, sulfite, fumarate, nitrate and nitrite were not used as terminal electron acceptors. Strain Ra1766G1(T) used cellobiose, glucose, mannose, maltose, arabinose, raffinose, galactose, ribose, sucrose, pyruvate and xylose as electron donors. The main fermentation product from glucose metabolism was acetate. The predominant cellular fatty acids were anteiso-C-15:0, iso-C-15:0, anteiso DMA-C-15:0 and C-16:0. The main polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, iso-DMA-C-15:0 glycolipids and phospholipids. The G+C content of the genomic DNA was 31.2 mol%. The closest phylogenetic relatives of strain Ra1766G1(T) were Natranaerovirga pectinivora AP3(T) (92.4 % 16S rRNA gene sequence similarity), Natranaerovirga hydrolytica APP2(T)(90.2 %) and Defluviitalea saccharophila 6LT2(T) (88.9 %). On the basis of phylogenetic inference and phenotypic properties, strain Ra1766G1(T) represents a novel species of a new genus for which the name Vallitalea guaymasensis is proposed. The type strain of the type species is Ra1766G1(T) (=DSM 24848(T)=JCM17997(T)).
    No preview · Article · Aug 2013
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    ABSTRACT: Magnetotactic bacteria (MTB) are capable of synthesizing intracellular organelles, the magnetosomes, that are membrane-bounded magnetite or greigite crystals arranged in chains. Although MTB are widely spread in various ecosystems, few axenic cultures are available, and only freshwater Magnetospirillum spp. have been genetically analysed. Here, we present the complete genome sequence of a marine magnetotactic spirillum, Magnetospira sp. QH-2. The high number of repeats and transposable elements account for the differences in QH-2 genome structure compared with other relatives. Gene cluster synteny and gene correlation analyses indicate that the insertion of the magnetosome island in the QH-2 genome occurred after divergence between freshwater and marine magnetospirilla. The presence of a sodium-quinone reductase, sodium transporters and other functional genes are evidence of the adaptive evolution of Magnetospira sp. QH-2 to the marine ecosystem. Genes well conserved among freshwater magnetospirilla for nitrogen fixation and assimilatory nitrate respiration are absent from the QH-2 genome. Unlike freshwater Magnetospirillum spp., marine Magnetospira sp. QH-2 neither has TonB and TonB-dependent receptors nor does it grow on trace amounts of iron. Taken together, our results show a distinct, adaptive evolution of Magnetospira sp. QH-2 to marine sediments in comparison with its closely related freshwater counterparts.
    Full-text · Article · Jun 2013 · Environmental Microbiology
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    ABSTRACT: An anaerobic thermophilic bacterium designated CA9F1 was isolated from a thermal spring in France. Strain CA9F1 was observed to grow at temperatures between 55 and 70 °C (optimum 65 °C) and at pH between 6.8 and 9.5 (optimum pH 7.4). Strain CA9F1 does not require salt for growth (0-10 g l(-1) NaCl), with an optimum at 1 g l(-1). The DNA G+C content was determined to be 38.5 mol% (Tm). The major cellular fatty acids identified were C15:0, C16:0, C17:0 iso. Based on phenotypic, chemotaxonomic and genotypic properties, strain CA9F1 was identified as Thermovenabulum gondwanense and this species was studied in more detail. Strain CA9F1 is a Gram-positive bacterium which forms a complex and regular multilayered cell wall structure, here characterised as being due to the presence of an S-layer. The network covers the entire cell surface and forms a hexagonal structure resembling that observed for Deinococcus radiodurans. The main protein component of the S-layer possesses domains comparable to that of the S-layer protein of Halothermothrix orenii. The characteristics of the strain were compared to that of T. gondwanese R270(T) isolated from microbial mats thriving in the thermal waters of a Great Artesian Basin bore runoff channel at 66 °C, in Australia. Significant differences were observed between CA9F1 and the type strain. One of the major physiological differences is the inability of CA9F1 to reduce Fe(III). An emended description of T. gondwanense is given.
    No preview · Article · Jun 2013 · Antonie van Leeuwenhoek
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    ABSTRACT: A novel obligately anaerobic, non-spore-forming, rod-shaped mesophilic, halophilic bacterium staining Gram-negative, was isolated from sediments of Guaymas basin. The strain, designated Ra1766G1T, grew at 20-40 °C (optimum 30-35 °C) and at pH 6.0-8.0 (optimum pH 6.5-7.5). It required 0.5%-7.5% NaCl (optimum 2%-3%) for growth. Sulfate, thiosulfate, elemental sulfur, sulfite, fumarate, nitrate and nitrite were not used as terminal electron acceptors. Strain Ra1766G1T used cellobiose, glucose, mannose, maltose, arabinose, raffinose, galactose, ribose, saccharose, pyruvate and xylose as electron donors. The main fermentation product from glucose metabolism was acetate. The predominant cellular fatty acids were anteiso-C15:0, iso-C15:0, anteiso DMA-C15:0 and C16:0. The main polar lipids consisted of diphosphatiglycerol, phosphatidylglycerol, glycolipids and phospholipids.The G+C content of the genomic DNA was 31.2 mol%. The closest phylogenetic relatives of Ra1766G1T were Natranaerovirga pectinivoraT (92.4% similarity), Natranaerovirga hydrolytica (90.2% similarity) and Defluviitalea saccharophilaT (88.9% similarity). On the basis of phylogenetic inference and phenotypic properties, strain Ra1766G1T (= DSM 24848T = JCMT= 16313) is proposed as the type strain of a novel species of a novel genus, Vallitalea guaymasensis gen. nov., sp. nov.
    Full-text · Article · Feb 2013 · International Journal of Systematic and Evolutionary Microbiology
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    ABSTRACT: Desulfovibrio piezophilus strain C1TLV30(T) is a piezophilic anaerobe that was isolated from wood falls in the Mediterranean deep-sea. D. piezophilus represents a unique model for studying the adaptation of sulfate-reducing bacteria to hydrostatic pressure. Here, we report the 3.6 Mbp genome sequence of this piezophilic bacterium. An analysis of the genome revealed the presence of seven genomic islands as well as gene clusters that are most likely linked to life at a high hydrostatic pressure. Comparative genomics and differential proteomics identified the transport of solutes and amino acids as well as amino acid metabolism as major cellular processes for the adaptation of this bacterium to hydrostatic pressure. In addition, the proteome profiles showed that the abundance of key enzymes that are involved in sulfate reduction was dependent on hydrostatic pressure. A comparative analysis of orthologs from the non-piezophilic marine bacterium D. salexigens and D. piezophilus identified aspartic acid, glutamic acid, lysine, asparagine, serine and tyrosine as the amino acids preferentially replaced by arginine, histidine, alanine and threonine in the piezophilic strain. This work reveals the adaptation strategies developed by a sulfate reducer to a deep-sea lifestyle.
    Full-text · Article · Jan 2013 · PLoS ONE
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    ABSTRACT: Desulfovibrio hydrothermalis AM13T is a piezophilic, mesophilic, hydrogenotrophic sulfate-reducing bacterium collected from a deep-sea hydrothermal chimney on the East Pacific Rise (2,600 m depth, 13°N). We report the genome sequence of this bacterium, which includes a 3,702,934-bp chromosome and a circular plasmid of 5,328 bp.
    Full-text · Article · Jan 2013 · Genome Announcements
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    ABSTRACT: pks genomic island of Escherichia coli is involved in the synthesis of the non-ribosomal peptide-type genotoxin colibactin, which has been suggesting as affecting the host immune response and having an impact on cancer development. The pks-encoded enzyme ClbP is an atypical peptidase that contributes to the synthesis of colibactin. In this work, we identified key features of ClbP. Bacterial fractionation and Western-blot analysis revealed the docking of ClbP to the bacterial inner membrane via a C-terminal domain harboring three predicted transmembrane helices. Whereas only one helix was necessary for the location in the inner membrane, the complete sequence of the C-terminal domain was necessary for ClbP bioactivity. In addition, the N-terminal sequence of ClbP allowed the SRP/Sec/YidC- and MreB-dependent translocation of the enzymatic domain in the periplasmic compartment, a feature also essential for ClbP bioactivity. Finally, the comparison of ClbP structure with that of the paralogs FmtA-like and AmpC revealed at an extremity of the catalytic groove a negative electrostatic potential surface characteristic of ClbP. Site-directed mutagenesis experiments identified in this zone two aspartic residues that were important for ClbP bioactivity. Overall, these results suggest a model for precolibactin activation by ClbP and pave a way for the design of inhibitors targeting colibactin production.
    No preview · Article · Oct 2012 · Journal of Molecular Biology
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    ABSTRACT: Enterohemorrhagic Escherichia coli (EHEC) are food-borne pathogens that can cause serious infections ranging from diarrhea to hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Translocation of Shiga-toxins (Stx) from the gut lumen to underlying tissues is a decisive step in the development of the infection, but the mechanisms involved remain unclear. Many bacterial pathogens target the follicle-associated epithelium, which overlies Peyer's patches (PPs), cross the intestinal barrier through M cells and are captured by mucosal macrophages. Here, translocation across M cells, as well as survival and proliferation of EHEC strains within THP-1 macrophages were investigated using EHEC O157:H7 reference strains, isogenic mutants, and 15 EHEC strains isolated from HC/HUS patients. We showed for the first time that E. coli O157:H7 strains are able to interact in vivo with murine PPs, to translocate ex vivo through murine ileal mucosa with PPs and across an in vitro human M cell model. EHEC strains are also able to survive and to produce Stx in macrophages, which induce cell apoptosis and Stx release. In conclusion, our results suggest that the uptake of EHEC by M cells and underlying macrophages in the PP may be a critical step in Stx translocation and release in vivo. A new model for EHEC infection in humans is proposed that could help in a fuller understanding of EHEC-associated diseases.
    Full-text · Article · Aug 2011 · PLoS ONE
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    ABSTRACT: The pks genomic island of Escherichia coli encodes polyketide (PK) and nonribosomal peptide (NRP) synthases that allow assembly of a putative hybrid PK-NRP compound named colibactin that induces DNA double-strand breaks in eukaryotic cells. The pks-encoded machinery harbors an atypical essential protein, ClbP. ClbP crystal structure and mutagenesis experiments revealed a serine-active site and original structural features compatible with peptidase activity, which was detected by biochemical assays. Ten ClbP homologs were identified in silico in NRP genomic islands of closely and distantly related bacterial species. All tested ClbP homologs were able to complement a clbP-deficient E. coli mutant. ClbP is therefore a prototype of a new subfamily of extracytoplasmic peptidases probably involved in the maturation of NRP compounds. Such peptidases will be powerful tools for the manipulation of NRP biosynthetic pathways.
    Full-text · Article · Jul 2011 · Journal of Biological Chemistry
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    ABSTRACT: Magnetotactic bacteria (MTB) mineralize nanosized magnetite or greigite crystals within cells and thus play an important role in the biogeochemical process. Despite decades of research, knowledge of MTB distribution and ecology, notably in areas subjected to oil industry activities, is still limited. In the present study, we investigated the presence of MTB in the Gulf of Fos, French Mediterranean coast, which is subjected to intensive oil industry activities. Microcosms containing sediments/water (1:2, v/v) from several sampling sites were monitored over several weeks. The presence of MTB was revealed in five of eight sites. Diverse and numerous MTB were revealed particularly from one site (named CAR), whilst temporal variations of a homogenous magnetotactic cocci population was shown within the LAV site microcosm over a 4-month period. Phylogenetic analysis revealed that they belonged to Alphaproteobacteria, and a novel genus from the LAV site was evidenced. Among the physicochemical parameters measured, a correlation was shown between the variation of MTB abundance in microcosms and the redox state of sulphur compounds.
    No preview · Article · Jul 2011 · Microbial Ecology
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    ABSTRACT: A novel sulfate-reducing bacterium, designated C1TLV30(T), was isolated from wood falls at a depth of 1693 m in the Mediterranean Sea. Cells were motile vibrios (2-4 × 0.5 µm). Strain C1TLV30(T) grew at temperatures between 15 and 45 °C (optimum 30 °C) and at pH 5.4-8.6 (optimum 7.3). It required NaCl for growth (optimum at 25 g NaCl l(-1)) and tolerated up to 80 g NaCl l(-1). Strain C1TLV30(T) used as energy sources: lactate, fumarate, formate, malate, pyruvate and ethanol. The end products from lactate oxidation were acetate, H(2)S and CO(2) in the presence of sulfate as terminal electron acceptor. Besides sulfate, thiosulfate and sulfite were also used as terminal electron acceptors, but not elemental sulfur, fumarate, nitrate or nitrite. Strain C1TLV30(T) possessed desulfoviridin and was piezophilic, growing optimally at 10 MPa (range 0-30 MPa). The membrane lipid composition of this strain was examined to reveal an increase in fatty acid chain lengths at high hydrostatic pressures. The G+C content of the genomic DNA was 49.6 % and the genome size was estimated at 3.5 ± 0.5 Mb. Phylogenetic analysis of the SSU rRNA gene sequence indicated that strain C1TLV30(T) was affiliated to the genus Desulfovibrio with Desulfovibrio profundus being its closest phylogenetic relative (similarity of 96.4 %). On the basis of SSU rRNA gene sequence comparisons and physiological characteristics, strain C1TLV30(T) ( = DSM 21447(T) = JCM 1548(T)) is proposed to be assigned to a novel species of the genus Desulfovibrio, Desulfovibrio piezophilus sp. nov.
    Full-text · Article · Feb 2010 · International Journal of Systematic and Evolutionary Microbiology
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    ABSTRACT: We report a multiplex real-time polymerase chain reaction method for detecting enterohemorrhagic Escherichia coli (EHEC) from strains or stool specimens. This assay detected the virulence genes stx1, stx2, and eae, without the use of probes. The method, which was validated on a collection of 143 EHEC strains, is simple, rapid, cost-effective, and sensitive.
    Preview · Article · Jun 2009 · Diagnostic microbiology and infectious disease

Publication Stats

933 Citations
126.06 Total Impact Points

Institutions

  • 2009-2015
    • Aix-Marseille Université
      • Laboratoire de Chimie Bactérienne (UMR 7283 LCB)
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2008-2015
    • University of Auvergne
      Clermont, Auvergne, France
    • French National Institute for Agricultural Research
      • Microbiologie (MIC)
      Lutetia Parisorum, Île-de-France, France
  • 2012
    • Institute of Research for Development
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2011
    • University Hospital Estaing of Clermont-Ferrand
      Clermont, Auvergne, France
  • 2003-2007
    • French National Centre for Scientific Research
      • Institut de Microbiologie de la Méditerranée
      Lutetia Parisorum, Île-de-France, France