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

RESULTS AND DISCUSSION
present work we have observed that the non virulent strain, EPOY-8803-II, shows
activity levels similar to the virulent strain.
As described before, information concerning mechanisms involved in the invasion
and survival of P. damselae subsp. piscicida inside the host is scarce and results
regarding interaction of this pathogen with phagocytes have been contradictory. For this
reason, pathogen survival after contact with sole phagocytes was evaluated. Results
included in article 1.2. (Article section) show that P. damselae subsp. piscicida is able to
survive inside sole phagocytes at least for five hours, survival rates being higher for the
virulent strain (62%) than the non virulent strain (19%). Also, higher survival rates were
observed in cultures with higher catalase activity. These results suggest that bacterial
inactivation could be due to the accumulation of hydrogen peroxide, the precursor of
hydroxyl radicals, after decomposition of superoxide radicals by bacterial superoxide
dismutase. Both virulent and non-virulent strains assayed by Barnes et al. (1999a)
showed high susceptibility to cell-free generated superoxide radicals, in contrast, we
have observed that a non-virulent strain, EPOY-8803-II, is significantly more
susceptible to killing by sole phagocytes than a virulent strain (Lg h41/01 ). Besides the
lower catalase activity present in the non-virulent strain, the lack of a capsule in cells of
EPOY-8803-II could contribute to the high inactivation rates observed. Thus, the capsule
could protect bacterial cells from oxidative radicals or even prevent activation of
phagocytes (Miller and Britigan, 1997; Arijo et al., 1998).
Finally, the important role of iron in microbial infections has been pointed out by
several authors (Miller and Britigan, 1997; Weinberg, 2000). P. damselae subsp.
piscicida is more susceptible to killing by sole phagocytes when bacterial cells have
been cultured under iron-depleted conditions. Bacteria require iron for growth and
replication and synthesize SOD and catalase to deal with oxidizing anions. P. damselae
subsp. piscicida posses a high-affinity iron uptake system, a syderophore (Magariños et
al. 1994; Naka et al., 2005). However, despite its ability to obtain iron from high-affinity
systems, several authors have reported that cells grown under iron-limited conditions
have reduced amounts of capsular material covering the cells (do Vale et al., 2001).
These cells with reduced capsule would be more susceptible to phagocytosis and
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