The antigenicity of Photobacterium damselae (Ph. d.)
subsp. piscicida, cultured in four different growth media
[tryptone soya broth (TSB), glucose-rich medium (GRM),
iron-depleted TSB (TSB + IR−), and iron-depleted GRM
(GRM + IR−)] was compared by enzyme-linked immunosorbent
assay (ELISA) and Western blot analysis using
sera obtained from sea bass (Dicentrarchus labrax) raised
against live or heat-killed Ph. d. subsp. piscicida. The
antigenic expression of Ph. d. subsp. piscicida was found to
differ depending on the culture medium used. A significantly
higher antibody response was obtained with iron-depleted
bacteria by ELISA compared with non-iron depleted
bacteria obtained from the sera of sea bass raised against
live Ph. d. subsp. piscicida. The sera from sea bass raised
against live bacteria showed a band at 22 kDa in bacteria
cultured in TSB + IR− or GRM+ IR− when bacteria that
had been freshly isolated from fish were used for the
screening, while bands at 24 and 47 kDa were observed
with bacteria cultured in TSB or GRM. When bacteria
were passaged several times on tryptic soya agar prior to
culturing in the four different media, only bands at 24 and
47 kDa were recognized, regardless of the medium used to
culture the bacteria. It would appear that the molecular
weight of Ph. d. subsp. piscicida antigens change in the
presence of iron restriction, and sera from sea bass
infected with live bacteria are able to detect epitopes on
the antigens after this shift in molecular weight.
