225
( 1894 ), who isolated the pathogen from diseased brown trout, obtained from a
hatchery in Germany, and named it ‘Bacillus der Forellenseuche’ or bacillus of trout
contagious disease. Because of the importance of the organism, some authors have
examined the early literature seeking evidence for the occurrence of furunculosis
prior to 1894 (Williamson 1928 ; McCarthy and Roberts 1980 ). However, although
several reports exist which suggest that furunculosis occurred earlier, it has proved
impossible because of poor descriptions, to be certain that the bacterial isolates in
question were Aer. salmonicida (Forel 1868 ; Fabre-Domerque 1890 ; Fischel and
Enoch 1892 ). In North America, the fi rst report of furunculosis was made by Marsh
( 1902 ) who described an organism, which was named as Bacillus truttae . This
caused an epizootic in hatchery fi sh in Michigan, U.S.A.
The placement of Aer. salmonicida in the bacterial taxonomic hierarchy should
be put into context. Like so many of the bacterial taxa described in the nineteenth
century, the organism has undergone a series of changes in its classifi cation. Shortly
after Emmerich and Weibel ( 1894 ) reported it, the pathogen was placed in the genus
Bacterium, as Bacterium salmonicida, by Lehmann and Neumann ( 1896 ). This was
probably its best known epithet before its eventual transfer to the genus Aeromonas .
To confuse the issue, however, Bacillus devorans (Zimmermann 1890 ), Bacterium
salmonica (Chester 1897 ), Bacterium truttae (Marsh 1902 ) and Bacillus salmonicida were also names assigned to the pathogen in the past. With the publication of
the 7th edition of Bergey’s Manual of Determinative Bacteriology in 1957, the
pathogen was transferred to the genus Aeromonas, then placed in the family
Pseudomonadaceae. Later, the genus Aeromonas was moved again, to the family
Vibrionaceae and more recently to its own family, i.e. the Aeromonadaceae (Colwell
et al. 1986 ). The initial re-classifi cation was based primarily on the work of Griffi n
et al. ( 1953a ). This team undertook the fi rst detailed characterisation of the organism, providing the information necessary to formulate the description, which
resulted in its re-classifi cation. However, the division of Aer. salmonicida strains
into subspecies remains an ongoing bone of taxonomic contention. The description
of Aer. salmonicida subsp. pectinolytica opens a new chapter in the understanding
of the organism insofar as this is the fi rst subspecies, which is not associated directly
with fi sh diseases (Pavan et al. 2000 ). Instead, the isolates were recovered from a
polluted river in Argentina (Pavan et al. 2000 ). To date, there is not any evidence to
link this subspecies with fi sh pathogenicity.
Two aspects concerned with the status of Aer. salmonicida in the bacterial taxonomic hierarchy require discussion. One centres on the intraspecifi c relationships of
Aer. salmonicida strains; the other is involved with questions that have been raised
regarding the retention of the species in the genus Aeromonas.
Aer. salmonicida has been known by its present name since the 1950s when, on
the basis of work by Griffi n et al. ( 1953a ), Snieszko ( 1957 ) in his contribution on
the genus Aeromonas in the 7th edition of Bergey’s Manual of Determinative
Bacteriology assigned the pathogen to this genus, where it has remained. It is curious, in view of its seriousness as a pathogen, that it was over 50 years from the initial discovery of the organism to the characterisation and description of Aer.
salmonicida. Griffi n et al. ( 1953a ) provided the fi rst detailed description of the
Aeromonas salmonicida
( 1894 ), who isolated the pathogen from diseased brown trout, obtained from a
hatchery in Germany, and named it ‘Bacillus der Forellenseuche’ or bacillus of trout
contagious disease. Because of the importance of the organism, some authors have
examined the early literature seeking evidence for the occurrence of furunculosis
prior to 1894 (Williamson 1928 ; McCarthy and Roberts 1980 ). However, although
several reports exist which suggest that furunculosis occurred earlier, it has proved
impossible because of poor descriptions, to be certain that the bacterial isolates in
question were Aer. salmonicida (Forel 1868 ; Fabre-Domerque 1890 ; Fischel and
Enoch 1892 ). In North America, the fi rst report of furunculosis was made by Marsh
( 1902 ) who described an organism, which was named as Bacillus truttae . This
caused an epizootic in hatchery fi sh in Michigan, U.S.A.
The placement of Aer. salmonicida in the bacterial taxonomic hierarchy should
be put into context. Like so many of the bacterial taxa described in the nineteenth
century, the organism has undergone a series of changes in its classifi cation. Shortly
after Emmerich and Weibel ( 1894 ) reported it, the pathogen was placed in the genus
Bacterium, as Bacterium salmonicida, by Lehmann and Neumann ( 1896 ). This was
probably its best known epithet before its eventual transfer to the genus Aeromonas .
To confuse the issue, however, Bacillus devorans (Zimmermann 1890 ), Bacterium
salmonica (Chester 1897 ), Bacterium truttae (Marsh 1902 ) and Bacillus salmonicida were also names assigned to the pathogen in the past. With the publication of
the 7th edition of Bergey’s Manual of Determinative Bacteriology in 1957, the
pathogen was transferred to the genus Aeromonas, then placed in the family
Pseudomonadaceae. Later, the genus Aeromonas was moved again, to the family
Vibrionaceae and more recently to its own family, i.e. the Aeromonadaceae (Colwell
et al. 1986 ). The initial re-classifi cation was based primarily on the work of Griffi n
et al. ( 1953a ). This team undertook the fi rst detailed characterisation of the organism, providing the information necessary to formulate the description, which
resulted in its re-classifi cation. However, the division of Aer. salmonicida strains
into subspecies remains an ongoing bone of taxonomic contention. The description
of Aer. salmonicida subsp. pectinolytica opens a new chapter in the understanding
of the organism insofar as this is the fi rst subspecies, which is not associated directly
with fi sh diseases (Pavan et al. 2000 ). Instead, the isolates were recovered from a
polluted river in Argentina (Pavan et al. 2000 ). To date, there is not any evidence to
link this subspecies with fi sh pathogenicity.
Two aspects concerned with the status of Aer. salmonicida in the bacterial taxonomic hierarchy require discussion. One centres on the intraspecifi c relationships of
Aer. salmonicida strains; the other is involved with questions that have been raised
regarding the retention of the species in the genus Aeromonas.
Aer. salmonicida has been known by its present name since the 1950s when, on
the basis of work by Griffi n et al. ( 1953a ), Snieszko ( 1957 ) in his contribution on
the genus Aeromonas in the 7th edition of Bergey’s Manual of Determinative
Bacteriology assigned the pathogen to this genus, where it has remained. It is curious, in view of its seriousness as a pathogen, that it was over 50 years from the initial discovery of the organism to the characterisation and description of Aer.
salmonicida. Griffi n et al. ( 1953a ) provided the fi rst detailed description of the
Aeromonas salmonicida