Brucellosis 2003 proceedings - PHIDIAS

Short Oral Communications
Immunology, pathogenesis and host-pathogen interaction
PO10- IivA, A PROTEIN INVOLVED IN THE Brucella spp. VIRULENCE.
S. L. Cravero, M. Carrica, E. Campos, A. Arese, J. Sabio y García, and O. L. Rossetti. Instituto de
Biotecnología, Instituto Nacional de Tecnología Agropecuaria (INTA), Buenos Aires, Argentina.
According with the analysis of Brucella melitensis 16M genome, 22 % of the
predicted ORFs have not an assigned function yet (Proc. Natl. Acad. Sci. USA 2002,
99:443). We report the characterization of one of this ORFs, that we named it iivA
(involved in virulence gene). This gene encodes for a protein of 11 kDa which
presents a high content of alfa-helix, as deduced by prediction of the secondary
structure using different algorithms and confirmed by circular dichroism of the
recombinant protein. Northern blot analysis suggested that iivA is monocystronic and
BLAST homology searches indicated that IivA have uncharacterized homologues in
Sinorhizobium meliloti and Agrobacterium tumefaciens.
Brucella abortus S2308 iivA and Brucella melitensis 16M iivA smooth strains
shown a severe attenuation both in the BALB/c mice and guinea pig models of
infection. When this strains were complemented in trans with a copy of the wild type
iivA gene, they recovered the full virulence. Using chemical crosslinking and a
bacterial two-hybrid system we shown that IivA can assembly in homomultimers. The
molecular bases of IivA function can contribute to understand the intimate
mechanisms of the Brucella virulence.
PO11- THE Brucella abortus xthA2 GENE PRODUCT CONTRIBUTES TO
RESISTANCE TO OXIDATIVE STRESS in vitro BUT IS NOT REQUIRED FOR
WILD-TYPE VIRULENCE IN THE MOUSE MODEL.
Michael L. Hornback and R. Martin Roop II. The Brody School of Medicine of East Carolina University.
USA.
Upon phagocytosis, Brucella abortus is able to reside within host
macrophages and survive the decrease in external pH, low nutrient availability, and
exposure to reactive oxygen intermediates (ROIs) encountered in the phagosomal
compartment. The reactive oxygen intermediates generated by the oxidative burst of
host macrophages are toxic to bacterial cells because these ROIs can react with
proteins, lipids, and DNA and the accumulation of these damaged molecules results
in death. In bacteria, there are two general defense mechanisms that are induced to
provide resistance to oxidative killing. The primary mechanism of defense against
ROIs involves enzymes that act directly to detoxify ROIs into harmless byproducts.
The secondary mechanism of defense includes enzymes involved in repair of
oxidatively damaged proteins, lipids, and DNA. Interestingly, studies involving
Salmonella suggest that the secondary defense mechanisms, specifically DNA
repair, may play a more important role in protecting bacteria from the oxidative burst
of host macrophages than primary protectants such as catalase. In Escherichia coli,
the base excision repair pathway is involved with repair of oxidatively damaged DNA.
A major component of the base excision repair pathway is exonuclease III, which is
encoded by the xthA gene. In E. coli, xthA mutants have been shown to be
hypersensitive to exposure of hydrogen peroxide suggesting this DNA repair pathway
is necessary for survival of this organism in response to ROIs.
Brucellosis 2003 International Research Conference
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