Brucellosis 2003 proceedings - PHIDIAS

Short Oral Communications
Immunology, pathogenesis and host-pathogen interaction
Analysis of the recently sequenced genome of Brucella melitensis 16M has
revealed the presence of two xthA homologs which has been designated xthA1 and
xthA2. An isogenic xthA2 mutant constructed from B. abortus 2308 exhibits
increased sensitivity to DNA damaging agents and hydrogen peroxide in vitro, but
displays wild-type virulence in cultured murine macrophages and experimentally
infected mice. These findings indicate that the xthA2 gene product contributes to the
resistance of B. abortus 2308 to oxidative damage but is not required for wild-type
virulence in the mouse model. The contributions of the xthA1 gene product to ROI
resistance and virulence are presently under investigation.
PO12- ANALYSIS OF Brucella ANTIOXIDANT GENES REVEALS THE
IMPORTANCE OF DEFENSE AGAINST STATIONARY PHASE ENDOGENOUS
REACTIVE OXYGEN INTERMEDIATE ACCUMULATION in vitro AND in vivo.
M. Wright Valderas, J. M. Gee, R. B. Alcantara, M. E. Kovach, J. E. Baumgartner, and R. M. Roop II.
Department of Microbiology and Immunology, East Carolina University School of Medicine, Greenville,
NC 27834, USA.
Brucellae are able to infect and replicate within host macrophages despite
encountering the oxidative burst, acidic pH, and nutrient deprivation. Enhancing the
amount of reactive oxygen intermediates (ROIs) produced during the macrophage
burst either by bacterial IgG opsonization or by macrophage activation with interferon
gamma fails to eliminate the intracellular brucellae in this cell type in culture.
Mutational analysis of the Brucella abortus antioxidant genes encoding catalase
(katE), superoxide dismutase (sodC), and alkyl hydroperoxide reductase (ahpCD)
has been undertaken, and the mutants assessed for ROI sensitivity in vitro and for
their ability to resist killing by in cultured murine macrophages and persistence in the
spleens of mice. While all three mutants were found to be sensitive to various ROI
generating compounds in in vitro assays, only the sodC and ahpCD mutants
demonstrated a defect in both their ability to replicate in cultured macrophages and to
establish and maintain the typical chronic spleen infection in mice. The sodC and
ahpCD genes are under the control of the stationary phase regulator Host Factor I
(HF-1) and require this protein for optimal expression, while katE is HF-1
independent. This link between antioxidant genes and stationary phase implies that
defense against the macrophage oxidative burst may be less important to the
bacterium’s ability to effectively colonize the host cell than the capacity of the
organism to detoxify endogenous ROIs which is key to its survival within its
environmental niche.
PO13- THE GLUTAMATE DECARBOXYLASE SYSTEM IN Brucella abortus IS
NOT REQUIRED FOR VIRULENCE IN THE MOUSE MODEL.
Tim Brown, Michelle Wright-Valderas, and R. Martin Roop II. East Carolina University, Brody School of
Medicine, Greenville, NC 27834, USA.
Brucella abortus is an extremely successful intracellular pathogen of humans
and domestic animals. This bacterium’s ability to cause disease is a direct result of
its ability to persist within host macrophages. It has been well documented that the
brucellae must withstand exposure to a low pH environment within the phagosome in
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Brucellosis 2003 International Research Conference