Papel de las actividades superóxido dismutasa y catalasa en la ...

INTRODUCTION
2.2. VIRULENCE MECHANISMS
Several virulence mechanisms have been described in P. damselae subsp. piscicida
that include production of extracellular products (ECPs) with haemolytic, phospholipase
and cytotoxic activities (Balebona et al., 1992; Magariños et al., 1992; Noya et al., 1995a
and b; Romalde, 2002; Bakopoulos et al., 2004). In addition, virulent strains constitutively
synthesize a thin layer of capsular material that confers resistance to serum killing and
decreases macrophage phagocytosis (Magariños et al., 1996b; Arijo et al., 1998; Acosta
et al., 2006).
A close relationship has been observed between capsule production and iron
availability. Thus, do Vale et al. (2001) observed that cells grown under iron-limiting
conditions always have significantly lower amounts of capsular material. This thinner
capsule probably results in a better exposure of the adhesins and iron receptors at the
bacterial surface during passage through circulatory system. Once the microorganism
reaches the different host tissues, the amount of capsular material probably increases in
response to host cellular defence mechanisms such as phagocytosis
3. SUPEROXIDE DISMUTASE AND CATALASE
ACTIVITIES AS VIRULENCE FACTORS
Bacterial inactivation within phagocytes takes place by two mechanisms: oxygen
independent mechanisms through phagocyte granule constituents (lysosomal enzymes,
catepsines, defensines, lactoferrine, proteolytic enzymes) and oxygen dependent
mechanisms. In the latter mechanisms oxygenic compounds such as hydrogen peroxide
(H 2 O 2 ), superoxide anion (O 2·- ) and hydroxyl radical (OH - ) takes place. These products
are generated during the called respiratory burst, due to the activation after phagocytosis
of nicotinamide-adenin-dinucleotide-phosphate-hydrogen (NADPH) oxidase located in
the membranes.
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