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Two Stable Variants of Burkholderia pseudomallei Strain MSHR5848 Express Broadly Divergent in vitro Phenotypes Associated with their Virulence Differences

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OSTP Journal Article

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USAMRIID Frederick United States

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Burkholderia pseudomallei Bp the biothreat agent of melioidosis, causes disease ranging from acute and rapidly fatal to protracted and chronic. Bp is highly infectious by aerosol, can cause severe disease with nonspecific symptoms, and is multiply antibiotic resistant. However, no vaccine exists. Unlike many Bp strains, which exhibit random variability in traits such as colony morphology, the Department of Defenses Unified Culture Collection solid medium-prepared stock of Bp strain MSHR5848 designated BURK178 exhibited two distinct and relatively stable colony morphologies on sheep blood agar plates a smooth, glossy, pale yellow colony type 1 and a flat dry white colony type 2. A stock prepared independently from one type 2 colony using liquid medium appeared to be phenotypically identical to the solid medium stock. Passage of these two variant colony types under standard laboratory conditions produced cultures composed 99.9 of the single corresponding type 1 or type 2 morphotype. However both types could switch to the other one at frequencies which varied with the growth condition. These MSHR5848 derivatives were extensively characterized to identify differences associated with type 1 and type 2 colony morphologies. 1 microscopic morphology, and colony morphology differences on each of six differential agar media were observed between the type 1 and the type 2 morphotype and only type 2 metabolized sugars in BCSA plates. 2-3 Antimicrobial susceptibilities and LPS features were characterized. 4 Biolog GEN III and phenotype microarray profiles revealed distinct metabolic and susceptibility differences between the variants. Analysis of the phenotype microarray narrowed the 1,920 substrates to a manageable subset which differentiates the two phenotypes. Furthermore, growth curves show that the type 1 variant grows more rapidly than the type 2 variant. 5 In mouse challenges, the type 2 variants exhibited 10-fold greater virulence than the type 1 var.

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  • Medicine and Medical Research
  • Microbiology
  • Genetic Engineering and Molecular Biology

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