Photobacterium damsela subsp. piscicida, the causative
agent of fish pasteurellosis, was grown in vivo.
Bacterial cells and extracellular products (ECPs)
were analysed via electrophoresis and immunoblot
analysis, using specific sea bass antisera. Growth
in vivo induced the synthesis of unique bacterial
cell proteins at >206, 206, 21.3, 18, 7.6 and
<7.6 kDa. Sea bass serum raised against live bacterial
cells of the pathogen and especially a sea bass
serum raised against formalin-inactivated bacterial
cells grown in a specific novel medium recognized
the novel antigens at >206 (associated with iron
sequestration), 21.3, 7.6 and <7.6 kDa, suggesting
that the latter medium conserves the synthesis of
natural bacterial cell proteins in vitro. In vivo
growth of the pathogen induced the synthesis of
more toxic ECPs in comparison with in vitro
growth and an inverse correlation between total
protein concentration in the ECPs and toxicity per
unit of protein was observed. Substrate-polyacrylamide
electrophoresis revealed the presence of
in vivo synthesized ECPs of the pathogen
(proteases) at 175, 132, <79 and 48.3 kDa. Histological
examination of tissues isolated from fish
injected with these ECPs revealed inflammatory and
necrotic lesions in the spleen, liver, head kidney,
intestine and heart as soon as 48 h post-introduction
of the ECPs.
