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Développement d'outils de typage moléculaire de haute résolution pour la détection et la différenciation de Bacillus anthracis

Abstract : Bacillus anthracis is a pathogenic bacterium with a worldwide repartition. It is the causative agent of a zoonosis named Anthrax. Belonging to the Bacillus genus, B. anthracis has the ability to sporulate: this particularity allows the bacterium to stay as quiescent spores into the soils and to resist against different kind of stresses (UV, heat treatment…). Mammals are principally infected and human or animal outbreaks are reported annually in the world. Several regions are endemic while some others, like France, report more sporadic cases. Even if Anthrax incidence is in constant decrease all over the world, B. anthracis is still a pathogen of interest for many countries because of its potential use as a biological weapon. The study of this bacterium has a two-tier purpose: first, it is the cause of a relative mortality in livestock and wildlife, and second it is potentially used as a weapon of mass destruction. This bacterial species is considered highly monomorphic and all strains are extremely closed genetically. In order to precisely identify strains during outbreaks or bioterrorism attempt and track the source of infection, several diagnosis and typing methods are available. However, not all of these methods have the discrimination power, the robustness or the ease of use that is required in the laboratory. During this work, I have studied the diversity of European isolates of B. anthracis. A whole genome sequencing approach for approximately 250 strains has been done with a great diversity into strains (France, Europe). A comparative bioinformatic analysis allowed genomes reconstruction and polymorphisms identification among European isolates (Single Nucleotide Polymorphism = SNP). These markers leaded to establish a precise phylogeny among 292 B. anthracis isolates at a world level. Several hypotheses concerning the origins and the evolution of this pathogen have been proposed. A new sublineage has been potentially discovered. A panel of sixty SNPs has been identified and confirmed to genotype the major groups and lineages phylogenetically related in Europe. Two molecular typing approaches based on PCR amplification have been developed. Using the identified SNP, they can be used to discriminate strains between each others. The first one is a quick and low cost approach (PCR HRM) whereas the second can be used to multiplex a lot of analyses (Luminex). My work allowed a significative increase into B. anthracis knowledge. The typing tools developed will allow traceability and quick identification of the strains involved in an Anthrax outbreak or in a suspected bioterrorist attempt in France.
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Guillaume Girault. Développement d'outils de typage moléculaire de haute résolution pour la détection et la différenciation de Bacillus anthracis. Biochimie, Biologie Moléculaire. AgroParisTech, 2015. Français. ⟨NNT : 2015AGPT0007⟩. ⟨tel-03081379⟩

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