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Abstract
Burkholderia pseudomallei, the etiologic agent of melioidosis, is a saprophytic bacterium that is commonly found in the soil and stagnant waters of tropical countries bordering the equator. Burkholderia mallei is a host-adapted clone of B. pseudomallei, which does not readily persist outside of its equine reservoir and causes the zoonotic disease known as glanders. Infection by these organisms occurs primarily via percutaneous inoculation or inhalation of contaminated aerosols. Acute infection with B. pseudomallei and B. mallei manifest as severe pneumonia that can lead to fatal septicemia. Not only are melioidosis and glanders difficult to diagnose and problematic to treat, but there is also no vaccine to protect against these pathogens; thus, there is significant concern that these pathogens could be used as biological warfare agents. For these reasons, the Federal Select Agent Program (SAP) has classified B. pseudomallei and B. mallei as Tier 1 Select Agents, and the United States Defense Threat Reduction Agency (DTRA) has prioritized the development of medical countermeasures (MCM) to protect against B. mallei and B. pseudomallei. To further our understanding of the pathogenesis of B. mallei and to aid in the development of MCM against B. mallei, improved large animal models are required. We validate the common marmoset as a suitable large animal model for studying intranasal infection with B. mallei. Additionally, we report on the characterization of two novel autotransporter (AT) proteins, BpaB and BatA, which we determined to be important virulence factors in the pathogenesis of B. mallei and potential vaccine candidates to protect against infection with B. mallei. Specifically, we identified BpaB to be an oligomeric AT that functions as a novel biofilm factor, and we characterized BatA to be a conventional AT that contributes to the intracellular survival of B. mallei in host macrophages and also functions as an acetylesterase. Furthermore, we also identify and characterize a novel live-attenuated strain of B. mallei ATCC 23344, which results in the production of a robust humoral immune response that protects against aerosol infection with B. mallei and B. pseudomallei.