220
In addition, Aer. salmonicida subsp. smithia has been recovered from ulcerative and
haemorrhagic conditions in Arctic charr in Austria with identifi cation of isolates
achieved by sequencing (Goldschmidt-Clermont et al. 2009 ).
Another variation of Aer. salmonicida infection, termed “head ulcer disease”, has
been described in Japanese eels (Hikada et al. 1983 ; Ohtsuka et al. 1984 ; Kitao et al.
1984 ). An atypical strain of Aer. salmonicida was implicated as the aetiological
agent. The progression of this disease is worthy of note because the pathogen is
apparently capable of causing mortalities solely as a result of localised proliferation, with no evidence for the development of a generalised septicaemia. Results of
natural and laboratory-based infections of eels with head ulcer disease revealed that
Aer. salmonicida was not recovered in signifi cant numbers from internal organs, i.e.
brain, kidney or spleen or, indeed, blood (Ohtsuka et al. 1984 ; Nakai et al. 1989a ).
However, the pathogen proliferated substantially in the muscle of eels (Nakai et al.
1989 ). Similar, localised ulcerative infections caused by atypical Aer. salmonicida
have been recognised in goldfi sh (Elliott and Shotts 1980 ) and carp (Csaba et al.
1981 ).
Isolation
Under ordinary circumstances, i.e. in cases of classical furunculosis caused by ‘typical’ strains of Aer. salmonicida, the pathogen may be readily recovered from diseased fi sh, especially from surface lesions and the kidney, by use of standard
non-selective bacteriological agar media. TSA has been commonly used for this
purpose. On TSA, the occurrence of colonies surrounded by a dark-brown watersoluble pigment (Fig. 5.7 ) after incubation at 20–25 °C for 3–4 days, is considered
as indicative of the presence of Aer. salmonicida . However, it must be remembered
that non-pigmented or slowly pigmented strains of the pathogen occur, and also that
some other bacteria produce diffusible brown pigments, e.g. Aer. hydrophila and
Aer. media . In addition, if the fi sh have succumbed to secondary infection with other
micro-organisms, isolation of Aer. salmonicida becomes much more diffi cult
because of overgrowth by other bacteria. Thus, growth of Aer. salmonicida may be
Fig. 5.6 An ulcerated goldfi sh on which the lesion has extended across the body wall, exposing
the underlying organs. The aetiological agent was atypical Aer. salmonicida
5 Aeromonadaceae Representative (Aeromonas salmonicida)
In addition, Aer. salmonicida subsp. smithia has been recovered from ulcerative and
haemorrhagic conditions in Arctic charr in Austria with identifi cation of isolates
achieved by sequencing (Goldschmidt-Clermont et al. 2009 ).
Another variation of Aer. salmonicida infection, termed “head ulcer disease”, has
been described in Japanese eels (Hikada et al. 1983 ; Ohtsuka et al. 1984 ; Kitao et al.
1984 ). An atypical strain of Aer. salmonicida was implicated as the aetiological
agent. The progression of this disease is worthy of note because the pathogen is
apparently capable of causing mortalities solely as a result of localised proliferation, with no evidence for the development of a generalised septicaemia. Results of
natural and laboratory-based infections of eels with head ulcer disease revealed that
Aer. salmonicida was not recovered in signifi cant numbers from internal organs, i.e.
brain, kidney or spleen or, indeed, blood (Ohtsuka et al. 1984 ; Nakai et al. 1989a ).
However, the pathogen proliferated substantially in the muscle of eels (Nakai et al.
1989 ). Similar, localised ulcerative infections caused by atypical Aer. salmonicida
have been recognised in goldfi sh (Elliott and Shotts 1980 ) and carp (Csaba et al.
1981 ).
Isolation
Under ordinary circumstances, i.e. in cases of classical furunculosis caused by ‘typical’ strains of Aer. salmonicida, the pathogen may be readily recovered from diseased fi sh, especially from surface lesions and the kidney, by use of standard
non-selective bacteriological agar media. TSA has been commonly used for this
purpose. On TSA, the occurrence of colonies surrounded by a dark-brown watersoluble pigment (Fig. 5.7 ) after incubation at 20–25 °C for 3–4 days, is considered
as indicative of the presence of Aer. salmonicida . However, it must be remembered
that non-pigmented or slowly pigmented strains of the pathogen occur, and also that
some other bacteria produce diffusible brown pigments, e.g. Aer. hydrophila and
Aer. media . In addition, if the fi sh have succumbed to secondary infection with other
micro-organisms, isolation of Aer. salmonicida becomes much more diffi cult
because of overgrowth by other bacteria. Thus, growth of Aer. salmonicida may be
Fig. 5.6 An ulcerated goldfi sh on which the lesion has extended across the body wall, exposing
the underlying organs. The aetiological agent was atypical Aer. salmonicida
5 Aeromonadaceae Representative (Aeromonas salmonicida)