528
lum. The signifi cance of these small cells is unclear, but they may represent a stage
in a life cycle, a laboratory artefact, or some form of survival mechanism.
The results of serology further complicated the understanding of V. anguillarum
(Bolinches et al. 1990 ). The establishment of serotypes has traversed species (or
phenetic) boundaries. Initially, three serotypes were recognised for isolates from
north western (USA) salmonids, Europe, and Pacifi c-north west (USA) (Pacha and
Kiehn 1969 ). This was supported by the work of Japanese scientists (Aoki et al.
1981 ; Muroga et al. 1984b ). With further study, the number of serotypes increased
to six (Kitao et al. 1983 ). Thus in a mammoth study of 267 isolates from ayu, eel
and rainbow trout, Kitao and co-workers defi ned serotypes A, B, C, D, E, and F as
a result of cross-agglutination and cross-absorption tests with thermo-stable ‘O’
(somatic) antigens. The majority (243) of these Japanese isolates were recovered in
serotype A. It is noteworthy, however, that avirulent isolates were not recovered in
any of these serotypes (Muroga et al. 1984b ). This refl ects the nature of the LPS in
the cell wall, which accounts for both the nature of the serotype (Johnson 1977 ;
Aoki et al. 1981 ) and the immunogenicity. Later, Sørensen and Larsen ( 1986 )
reported the presence of 10 O-antigen serotypes, based upon examination of 495
isolates, representatives of which shared a common 40 kDa protein (Simón et al.
1996 ). A common 47 kb plasmid was reported by Giles et al. ( 1995 ). Serovars 01
and 02 contained plasmids, but there was no apparent correlation between the presence of such extrachromosomal DNA and biochemical properties (Larsen and Olsen
1991 ), although serogroup O1 was regarded as biochemically homogeneous
(Pedersen and Larsen 1995 ). The same 10 serogroups together with 6 nontypeable
groups were described by Olsen and Larsen (1993). The number of serogroups was
now increased to 23, i.e. O1 to O23 (Silva-Rubio et al. 2008 ).
A consensus view would be that serogroup O1 has dominated both in the number
of isolates available for study and the relative importance to fi sh pathology (Austin
et al. 1995a ; Pedersen et al. 1996a , b ). The homogeneity of serogroup O1 has been
established (Austin et al. 1995a ), yet data have pointed to variability among isolates.
For example, after studying 75 isolates of serogroup O1, 8 plasmid profi les – with
one predominating – and 6 ribotypes were recognised (Skov et al. 1995 ). An even
larger examination of 103 isolates of serogroup O1 recognised 15 plasmid profi les
(Pedersen and Larsen 1995 ). PFGE had high discriminatory power, recognising 35
profi les.
It is a personal view that isolates of serogroup O2 have seemed to be more
aggressive than serogroup O1, with the former developing into a signifi cant pathogen of farmed cod in Norway. Serogroup O2, which has been subdivided into serogroup O2a and O2b (e.g. Mikkelsen et al. 2007 ), has revealed heterogeneity in LPS
profi les – six different profi les have been recognised among 129 isolates (Tiainen
et al. 1997 ). By western blotting and slide agglutination, four different patterns have
emerged. By comparing LPS profi ling, western blotting and slide agglutination,
nine different groupings were formed (Tiainen et al. 1997 ). A view was expressed
that additional sub-groups within serogroup O2 remain to be described (Tiainen
et al. 1997 ). Serotype O3, which was comparatively uncommon, appears to be
10 Vibrios
lum. The signifi cance of these small cells is unclear, but they may represent a stage
in a life cycle, a laboratory artefact, or some form of survival mechanism.
The results of serology further complicated the understanding of V. anguillarum
(Bolinches et al. 1990 ). The establishment of serotypes has traversed species (or
phenetic) boundaries. Initially, three serotypes were recognised for isolates from
north western (USA) salmonids, Europe, and Pacifi c-north west (USA) (Pacha and
Kiehn 1969 ). This was supported by the work of Japanese scientists (Aoki et al.
1981 ; Muroga et al. 1984b ). With further study, the number of serotypes increased
to six (Kitao et al. 1983 ). Thus in a mammoth study of 267 isolates from ayu, eel
and rainbow trout, Kitao and co-workers defi ned serotypes A, B, C, D, E, and F as
a result of cross-agglutination and cross-absorption tests with thermo-stable ‘O’
(somatic) antigens. The majority (243) of these Japanese isolates were recovered in
serotype A. It is noteworthy, however, that avirulent isolates were not recovered in
any of these serotypes (Muroga et al. 1984b ). This refl ects the nature of the LPS in
the cell wall, which accounts for both the nature of the serotype (Johnson 1977 ;
Aoki et al. 1981 ) and the immunogenicity. Later, Sørensen and Larsen ( 1986 )
reported the presence of 10 O-antigen serotypes, based upon examination of 495
isolates, representatives of which shared a common 40 kDa protein (Simón et al.
1996 ). A common 47 kb plasmid was reported by Giles et al. ( 1995 ). Serovars 01
and 02 contained plasmids, but there was no apparent correlation between the presence of such extrachromosomal DNA and biochemical properties (Larsen and Olsen
1991 ), although serogroup O1 was regarded as biochemically homogeneous
(Pedersen and Larsen 1995 ). The same 10 serogroups together with 6 nontypeable
groups were described by Olsen and Larsen (1993). The number of serogroups was
now increased to 23, i.e. O1 to O23 (Silva-Rubio et al. 2008 ).
A consensus view would be that serogroup O1 has dominated both in the number
of isolates available for study and the relative importance to fi sh pathology (Austin
et al. 1995a ; Pedersen et al. 1996a , b ). The homogeneity of serogroup O1 has been
established (Austin et al. 1995a ), yet data have pointed to variability among isolates.
For example, after studying 75 isolates of serogroup O1, 8 plasmid profi les – with
one predominating – and 6 ribotypes were recognised (Skov et al. 1995 ). An even
larger examination of 103 isolates of serogroup O1 recognised 15 plasmid profi les
(Pedersen and Larsen 1995 ). PFGE had high discriminatory power, recognising 35
profi les.
It is a personal view that isolates of serogroup O2 have seemed to be more
aggressive than serogroup O1, with the former developing into a signifi cant pathogen of farmed cod in Norway. Serogroup O2, which has been subdivided into serogroup O2a and O2b (e.g. Mikkelsen et al. 2007 ), has revealed heterogeneity in LPS
profi les – six different profi les have been recognised among 129 isolates (Tiainen
et al. 1997 ). By western blotting and slide agglutination, four different patterns have
emerged. By comparing LPS profi ling, western blotting and slide agglutination,
nine different groupings were formed (Tiainen et al. 1997 ). A view was expressed
that additional sub-groups within serogroup O2 remain to be described (Tiainen
et al. 1997 ). Serotype O3, which was comparatively uncommon, appears to be
10 Vibrios