237
persistent agglutination of the strains in saline. This problem was circumvented by
Blake and Anderson ( 1930 ), who employed complement fi xation for the examination of 82 isolates of Aer. salmonicida. All of these isolates gave a positive response.
Ewing et al. ( 1961 ) examined agglutinin absorption with reference to ‘O’ and ‘H’
antigens. They concluded that the 21 strains examined were related to each other,
but also to a strain of Aer. hydrophila (O-antigen suspensions prepared using the 21
cultures reacted to ca. 25 % of the titre of the O-antiserum prepared with Aer.
hydrophila ) . Other researchers have also found serological homogeneity among
strains of Aer. salmonicida, but some degree of cross-reactivity with Aer. hydrophila. For example, common antigens among two Aer. salmonicida strains, as determined by gel-diffusion, and cross-reactions between Aer. salmonicida antiserum
and three out of four isolates of Aer. hydrophila, but not of Aer. salmonicida strains
and Aer. hydrophila antiserum, was reported by Liu ( 1961 ). Karlsson ( 1962 ), using
the antigenic properties of a haemolysin from Aer. salmonicida, found no serological differences among the six strains tested. Although these six strains did not crossreact with other aeromonads recovered from humans, it was later established that
there were indeed common thermolabile antigens between Aer. salmonicida and
other Aeromonas species as assessed using precipitin, agglutination and double diffusion precipitin tests. Bullock ( 1966 ) also found evidence of cross-reactions
between soluble antigens of Aer. salmonicida and Aer. hydrophila. Serological
cross-reactions between casein-precipitating enzymes of these two Aeromonas species were reported by Snadvick and Hagan ( 1968 ). Within the Aer. salmonicida
group, Popoff ( 1969 ) found no serological differences among large numbers of typical pigment-producing isolates. Indeed, Popoff ( 1984 ), citing the work of Karlsson
( 1964 ), Spence et al. ( 1965 ) and his own previous studies, concluded that Aer. salmonicida is a serologically homogeneous species. Several workers have, in contrast,
reported antigenic differences within the species (Duff 1939 ; Liu 1961 ; Klontz and
Anderson 1968 ; Kimura 1969b ). Paterson et al. ( 1980 ) considered that these confl icting fi ndings refl ected the choice of cultures, because comparable methodology
had been used throughout. This group also reported results similar to those of
Kimura ( 1969a , b ), suggesting that Aer. salmonicida may be separated serologically
into two groups based upon antigenicity of a given strain. In their studies, Aer. salmonicida NCIMB 1110 and 1102 and Aer. salmonicida subsp. masoucida contained
an extra antigenic component, termed the ‘c’ component. Kimura ( 1969b ) demonstrated the heat-sensitivity of an additional antigenic component (shared with Aer.
hydrophila ) in the subspecies masoucida. Klontz and Anderson ( 1968 ) observed
smears prepared from 24 cultures of Aer. salmonicida with three antisera, by means
of an indirect FAT. They postulated the existence of at least seven different serotypes, based upon non-reactivity of certain strains with one or more of the antisera.
However, McCarthy and Roberts ( 1980 ) questioned the suitability of this technique
for serological analysis of laboratory cultures, due to the potential for technical
diffi culties.
McCarthy and Rawle ( 1975 ) carried out an extensive serological study of both
thermolabile and thermostable somatic antigens of Aer. salmonicida and their relationship to other bacteria. They employed whole-cell agglutination and double
Aeromonas salmonicida
persistent agglutination of the strains in saline. This problem was circumvented by
Blake and Anderson ( 1930 ), who employed complement fi xation for the examination of 82 isolates of Aer. salmonicida. All of these isolates gave a positive response.
Ewing et al. ( 1961 ) examined agglutinin absorption with reference to ‘O’ and ‘H’
antigens. They concluded that the 21 strains examined were related to each other,
but also to a strain of Aer. hydrophila (O-antigen suspensions prepared using the 21
cultures reacted to ca. 25 % of the titre of the O-antiserum prepared with Aer.
hydrophila ) . Other researchers have also found serological homogeneity among
strains of Aer. salmonicida, but some degree of cross-reactivity with Aer. hydrophila. For example, common antigens among two Aer. salmonicida strains, as determined by gel-diffusion, and cross-reactions between Aer. salmonicida antiserum
and three out of four isolates of Aer. hydrophila, but not of Aer. salmonicida strains
and Aer. hydrophila antiserum, was reported by Liu ( 1961 ). Karlsson ( 1962 ), using
the antigenic properties of a haemolysin from Aer. salmonicida, found no serological differences among the six strains tested. Although these six strains did not crossreact with other aeromonads recovered from humans, it was later established that
there were indeed common thermolabile antigens between Aer. salmonicida and
other Aeromonas species as assessed using precipitin, agglutination and double diffusion precipitin tests. Bullock ( 1966 ) also found evidence of cross-reactions
between soluble antigens of Aer. salmonicida and Aer. hydrophila. Serological
cross-reactions between casein-precipitating enzymes of these two Aeromonas species were reported by Snadvick and Hagan ( 1968 ). Within the Aer. salmonicida
group, Popoff ( 1969 ) found no serological differences among large numbers of typical pigment-producing isolates. Indeed, Popoff ( 1984 ), citing the work of Karlsson
( 1964 ), Spence et al. ( 1965 ) and his own previous studies, concluded that Aer. salmonicida is a serologically homogeneous species. Several workers have, in contrast,
reported antigenic differences within the species (Duff 1939 ; Liu 1961 ; Klontz and
Anderson 1968 ; Kimura 1969b ). Paterson et al. ( 1980 ) considered that these confl icting fi ndings refl ected the choice of cultures, because comparable methodology
had been used throughout. This group also reported results similar to those of
Kimura ( 1969a , b ), suggesting that Aer. salmonicida may be separated serologically
into two groups based upon antigenicity of a given strain. In their studies, Aer. salmonicida NCIMB 1110 and 1102 and Aer. salmonicida subsp. masoucida contained
an extra antigenic component, termed the ‘c’ component. Kimura ( 1969b ) demonstrated the heat-sensitivity of an additional antigenic component (shared with Aer.
hydrophila ) in the subspecies masoucida. Klontz and Anderson ( 1968 ) observed
smears prepared from 24 cultures of Aer. salmonicida with three antisera, by means
of an indirect FAT. They postulated the existence of at least seven different serotypes, based upon non-reactivity of certain strains with one or more of the antisera.
However, McCarthy and Roberts ( 1980 ) questioned the suitability of this technique
for serological analysis of laboratory cultures, due to the potential for technical
diffi culties.
McCarthy and Rawle ( 1975 ) carried out an extensive serological study of both
thermolabile and thermostable somatic antigens of Aer. salmonicida and their relationship to other bacteria. They employed whole-cell agglutination and double
Aeromonas salmonicida