AUTHOR=Bozue Joel A. , Chaudhury Sidhartha , Amemiya Kei , Chua Jennifer , Cote Christopher K. , Toothman Ronald G. , Dankmeyer Jennifer L. , Klimko Christopher P. , Wilhelmsen Catherine L. , Raymond Jolynn W. , Zavaljevski Nela , Reifman Jaques , Wallqvist Anders 

TITLE=Phenotypic Characterization of a Novel Virulence-Factor Deletion Strain of Burkholderia mallei That Provides Partial Protection against Inhalational Glanders in Mice

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=6

YEAR=2016

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2016.00021

DOI=10.3389/fcimb.2016.00021

ISSN=2235-2988

ABSTRACT=<p><italic>Burkholderia mallei</italic> (<italic>Bm</italic>) is a highly infectious intracellular pathogen classified as a category B biological agent by the Centers for Disease Control and Prevention. After respiratory exposure, <italic>Bm</italic> establishes itself within host macrophages before spreading into major organ systems, which can lead to chronic infection, sepsis, and death. Previously, we combined computational prediction of host-pathogen interactions with yeast two-hybrid experiments and identified novel virulence factor genes in <italic>Bm</italic>, including <italic>BMAA0</italic>553, <italic>BMAA0728</italic> (<italic>tssN</italic>), and <italic>BMAA1865</italic>. In the present study, we used recombinant allelic exchange to construct deletion mutants of <italic>BMAA0553</italic> and <italic>tssN</italic> (ΔBMAA0553 and ΔTssN, respectively) and showed that both deletions completely abrogated virulence at doses of &gt;100 times the LD<sub>50</sub> of the wild-type <italic>Bm</italic> strain. Analysis of ΔBMAA0553- and ΔTssN-infected mice showed starkly reduced bacterial dissemination relative to wild-type <italic>Bm</italic>, and subsequent <italic>in vitro</italic> experiments characterized pathogenic phenotypes with respect to intracellular growth, macrophage uptake and phagosomal escape, actin-based motility, and multinucleated giant cell formation. Based on observed <italic>in vitro</italic> and <italic>in vivo</italic> phenotypes, we explored the use of ΔTssN as a candidate live-attenuated vaccine. Mice immunized with aerosolized ΔTssN showed a 21-day survival rate of 67% after a high-dose aerosol challenge with the wild-type <italic>Bm</italic> ATCC 23344 strain, compared to a 0% survival rate for unvaccinated mice. However, analysis of histopathology and bacterial burden showed that while the surviving vaccinated mice were protected from acute infection, <italic>Bm</italic> was still able to establish a chronic infection. Vaccinated mice showed a modest IgG response, suggesting a limited potential of ΔTssN as a vaccine candidate, but also showed prolonged elevation of pro-inflammatory cytokines, underscoring the role of cellular and innate immunity in mitigating acute infection in inhalational glanders.</p>