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

RESULTS AND DISCUSSION
The first objective of this PhD. Thesis consisted in the study of the contribution of
superoxide dismutase and catalase activities to Photobacterium damselae subsp.
piscicida resistance against oxygenic radicals generated during respiratory burst in sole
phagocytes and, therefore, their possible role as virulence factors (articles 1.1. and 1.2.,
Article section).
Previously, Barnes et al. (1999a) demonstrated in vitro that this microorganism
contains enough superoxide dismutase activity to disproportionate photochemically
generated superoxide anions, and that the bacterial susceptibility is due to the action of
hydrogen peroxide. In fact, the addition of exogenous catalase to the medium protected
the bacteria from inactivation by superoxide anions. The role of catalase and superoxide
dismutase activities in P. damselae subsp. piscicida virulence has been studied in this
work and results are included in articles 1.1. and 1.2. (Article section).
In vitro role of catalase activity in P. damselae subsp. piscicida protection against
exogenous hydrogen peroxide has been evaluated in the first article. Results obtained
show that resistance to hydrogen peroxide increases when bacterial cultures are pulsed
with hydrogen peroxide. On the contrary, survival percentages decrease when bacteria
grow under iron-limiting conditions. Quantification of catalase activity in a set of P.
damselae subsp. piscicida strains shows that highest survival percentages are present in
bacterial cultures with higher catalase activity levels. Moreover, resistance to oxidative
stress varied depending on the virulence, being higher in more virulent strains. Thus, the
virulent strain Lg h41/01 shows higher resistance to respiratory burst of sole phagocytes
than the non virulent strain EPOY-8803-II, and hydrogen peroxide addition into cultures
increases survival. The lack of cell capsule could contribute to the decrease of survival
against reactive oxygen species, but the low levels of catalase activity obtained in
EPOY-8803-II, suggest that its absence of virulence could be determined, in great part,
by low catalase activity. Therefore, catalase plays an important role in P. damselae
subsp. piscicida virulence. It has been demonstrated, in a great number of bacteria, that
previous exposition to an oxidant in sublethal concentrations can induce protection
against lethal concentrations of the oxidant (Mongkolsuk et al., 1996). Barnes et al.
(1999b) reported that after being pulsed with hydrogen peroxide A. salmonicida is able to
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