235
are regularly reported. Debate has centred on the relationship of Aer. salmonicida
within the genus Aeromonas. In the study by Eddy ( 1960 ), attention was focused on
the inability of Aer. salmonicida to produce 2,3-butanediol from glucose, and the
absence of motility, both characters of which contravened the genus description of
Kluyver and van Niel ( 1936 ). However, Eddy did not dispute the retention of Aer.
salmonicida within the genus. Instead, this placement was challenged by Smith
( 1963 ), who expressed doubt as to whether Aer. salmonicida belonged in the genus
Aeromonas. Her recommendation was the establishment of a new genus, i.e.
Necromonas, with two species, namely Nec. salmonicida for the typical isolates and
Nec. achromogenes for the non-pigmented strains. The evidence appertained to the
morphological, biochemical and metabolic traits of 42 isolates of ‘Bacterium salmonicida’, six non-pigmented pathogens, and 42 other bacterial cultures. Thus,
there were pronounced differences between Bacterium salmonicida and other
Aeromonas cultures. It emphasised, for instance, that the production of gas from
glucose was an important genus characteristic. Although many previous reports had
stated that the pathogen produced gas from glucose (Griffi n et al. 1953a ; Eddy
1960 , 1962 ; Ewing et al. 1961 ; Schubert 1961 ), the hundreds of isolates examined
at the Marine Laboratory, Aberdeen, between 1953 and 1962 produced either very
little or no gas from glucose. Instead, they produced gas from mannitol (Smith
1963 ). As for the production of 2,3-butanediol from glucose, Smith ( 1963 ) contended that previously this test required a tedious procedure, and consequently was
often not applied to presumptive aeromonads. However, in her laboratory, Bacterium
salmonicida isolates did not so produce the compound. Due to such discrepancies
with the genus description, it was proposed that the species should be removed from
the genus Aeromonas and placed in a new genus, i.e. Necromonas. Although Smith’s
proposal was not formally adopted, it should be mentioned that Cowan ( 1974 ) followed her suggested classifi cation, by including Nec. salmonicida in the diagnostic
tables. However, it is our opinion that the deviations of Aer. salmonicida from the
initial genus description of Aeromonas should, for several reasons, be viewed less
stringently than may be to the approval of some taxonomist purists. For example, it
is often a diffi cult decision in bacterial systematics as to how much variation to
allow within the defi nition of a species or a genus, before the line is drawn and relationships, or lack of, declared. If examples are taken from the characteristics of
motile aeromonads, it is certainly the case that discrepancies occur for some members of these species as regards agreement with the genus description (HolderFranklin et al. 1981 ; Allen et al. 1983b ). Schubert ( 1974 ) included the production of
2,3-butanediol (a generic trait) as occurring in some species. Non-motility is also
taken into account, and carbohydrates are cited as being broken down to acid or to
acid and gas. These modifi cations to the genus description thus eliminate the major
objections of Smith ( 1963 ) regarding the retention of Aer. salmonicida within the
genus Aeromonas . In addition, subsequent serological and bacteriophage sensitivity
data have provided strong evidence for a relationship between Aer. salmonicida and
the motile aeromonads. The existence of a common antigen between Aer. hydrophila and Aer. salmonicida subsp. masoucida and some other strains of Aer. salmonicida was demonstrated by Kimura ( 1969b ) and Paterson et al. ( 1980 ). In an
Aeromonas salmonicida
are regularly reported. Debate has centred on the relationship of Aer. salmonicida
within the genus Aeromonas. In the study by Eddy ( 1960 ), attention was focused on
the inability of Aer. salmonicida to produce 2,3-butanediol from glucose, and the
absence of motility, both characters of which contravened the genus description of
Kluyver and van Niel ( 1936 ). However, Eddy did not dispute the retention of Aer.
salmonicida within the genus. Instead, this placement was challenged by Smith
( 1963 ), who expressed doubt as to whether Aer. salmonicida belonged in the genus
Aeromonas. Her recommendation was the establishment of a new genus, i.e.
Necromonas, with two species, namely Nec. salmonicida for the typical isolates and
Nec. achromogenes for the non-pigmented strains. The evidence appertained to the
morphological, biochemical and metabolic traits of 42 isolates of ‘Bacterium salmonicida’, six non-pigmented pathogens, and 42 other bacterial cultures. Thus,
there were pronounced differences between Bacterium salmonicida and other
Aeromonas cultures. It emphasised, for instance, that the production of gas from
glucose was an important genus characteristic. Although many previous reports had
stated that the pathogen produced gas from glucose (Griffi n et al. 1953a ; Eddy
1960 , 1962 ; Ewing et al. 1961 ; Schubert 1961 ), the hundreds of isolates examined
at the Marine Laboratory, Aberdeen, between 1953 and 1962 produced either very
little or no gas from glucose. Instead, they produced gas from mannitol (Smith
1963 ). As for the production of 2,3-butanediol from glucose, Smith ( 1963 ) contended that previously this test required a tedious procedure, and consequently was
often not applied to presumptive aeromonads. However, in her laboratory, Bacterium
salmonicida isolates did not so produce the compound. Due to such discrepancies
with the genus description, it was proposed that the species should be removed from
the genus Aeromonas and placed in a new genus, i.e. Necromonas. Although Smith’s
proposal was not formally adopted, it should be mentioned that Cowan ( 1974 ) followed her suggested classifi cation, by including Nec. salmonicida in the diagnostic
tables. However, it is our opinion that the deviations of Aer. salmonicida from the
initial genus description of Aeromonas should, for several reasons, be viewed less
stringently than may be to the approval of some taxonomist purists. For example, it
is often a diffi cult decision in bacterial systematics as to how much variation to
allow within the defi nition of a species or a genus, before the line is drawn and relationships, or lack of, declared. If examples are taken from the characteristics of
motile aeromonads, it is certainly the case that discrepancies occur for some members of these species as regards agreement with the genus description (HolderFranklin et al. 1981 ; Allen et al. 1983b ). Schubert ( 1974 ) included the production of
2,3-butanediol (a generic trait) as occurring in some species. Non-motility is also
taken into account, and carbohydrates are cited as being broken down to acid or to
acid and gas. These modifi cations to the genus description thus eliminate the major
objections of Smith ( 1963 ) regarding the retention of Aer. salmonicida within the
genus Aeromonas . In addition, subsequent serological and bacteriophage sensitivity
data have provided strong evidence for a relationship between Aer. salmonicida and
the motile aeromonads. The existence of a common antigen between Aer. hydrophila and Aer. salmonicida subsp. masoucida and some other strains of Aer. salmonicida was demonstrated by Kimura ( 1969b ) and Paterson et al. ( 1980 ). In an
Aeromonas salmonicida