412
The intraspecifi c diversity of 10 isolates was examined by means of 16S rRNA
gene sequencing and RFLP, and three genomic groups recognised of which most
cultures were recovered in Group 1. Interestingly, the 3 isolates in Group 3 contained a ~370 bp fragment that was absent from the other cultures (Schneck and
Caslake 2006 ). Arias et al. ( 2004 ) evaluated 30 fi sh isolates and reference cultures
by 16S rDNA sequencing, AFLP and intergenic spacer region sequencing, and
defi ned two predominating genomovars (I and II) although the intergenic spacer
region (ISR) sequencing revealed a higher diversity among genomovar I representatives, and by AFLP 22 profi les were recognised. Of interest, 4 isolates from tilapia
in Brazil were recovered in a separate group, albeit related to genomovar I and
II. Using a similar approach and 30 Finnish isolates plus the type strain, (Suomalainen
et al. 2006a ), the outcome was that the isolates were recovered in a genomovar
although 8 ARISA profi les were defi ned of which three were similar. In a later
study, Olivares-Fuster et al. ( 2007 ) studied 90 isolates predominantly from Alabama,
USA, and defi ned genomovar status on the basis of RFLP analyses and other genotyping approaches, i.e. ALFP, MLSA and ISR-SSCP with the outcome that two
groupings [genomovar I and II] were recognised of which there was higher genetic
diversity in the latter. Interestingly, most of genomovar I was from threadfi n shad
whereas genomovar II isolates were mostly from catfi sh (Olivares-Fuster et al.
2007 ). In catfi sh farms in southeastern USA, Fla. columnare were recovered from
columnaris outbreaks during spring 2010 to summer 2012 and determined to be of
genomovar II (Mohammed and Arias 2014 ).
Fla. columnare may display Rhizoidal and Rough colony morphotypes, which
are associated with virulence and resistance to starvation/bacteriophages, respectively (Zhang et al. 2014 ). The Rough colonies may arise spontaneously, or are
induced by infection with bacteriophages, and have been demonstrated to be more
susceptible to predation by amoebae and ciliates, and produced more biofi lm (in the
presence of amoebae) (Zhang et al. 2014 ). A third morphotype has been described
as “Soft” (Laanto et al. 2014 ). By electron microscopy, the cells of Rhizoid and Soft
but not so Rough morphotypes displayed an organised structure, which may be
related to gliding motility; a refl ection of virulence properties. Planktonic cells of
the Rhizoid and Rough but not Soft colonies produced large membrane vesicles that
contained two proteins, i.e. OmpA and SprF, and may be associated with adhesion
and possibly invasion, and gliding motility, respectively. Also, the Rhizoid morphotype secreted a small, unidentifi ed 13 kDa protein, possibly related to virulence
(Laanto et al. 2014 ).
Diagnosis
Phenotypic Methods A simplistic approach has involved the observation of wet
preparations, prepared from lesion material, which were supposed to demonstrate
the presence of ‘column’ – like masses of bacteria (Snieszko 1958b ).
7 Flavobacteria and Cytophagas
The intraspecifi c diversity of 10 isolates was examined by means of 16S rRNA
gene sequencing and RFLP, and three genomic groups recognised of which most
cultures were recovered in Group 1. Interestingly, the 3 isolates in Group 3 contained a ~370 bp fragment that was absent from the other cultures (Schneck and
Caslake 2006 ). Arias et al. ( 2004 ) evaluated 30 fi sh isolates and reference cultures
by 16S rDNA sequencing, AFLP and intergenic spacer region sequencing, and
defi ned two predominating genomovars (I and II) although the intergenic spacer
region (ISR) sequencing revealed a higher diversity among genomovar I representatives, and by AFLP 22 profi les were recognised. Of interest, 4 isolates from tilapia
in Brazil were recovered in a separate group, albeit related to genomovar I and
II. Using a similar approach and 30 Finnish isolates plus the type strain, (Suomalainen
et al. 2006a ), the outcome was that the isolates were recovered in a genomovar
although 8 ARISA profi les were defi ned of which three were similar. In a later
study, Olivares-Fuster et al. ( 2007 ) studied 90 isolates predominantly from Alabama,
USA, and defi ned genomovar status on the basis of RFLP analyses and other genotyping approaches, i.e. ALFP, MLSA and ISR-SSCP with the outcome that two
groupings [genomovar I and II] were recognised of which there was higher genetic
diversity in the latter. Interestingly, most of genomovar I was from threadfi n shad
whereas genomovar II isolates were mostly from catfi sh (Olivares-Fuster et al.
2007 ). In catfi sh farms in southeastern USA, Fla. columnare were recovered from
columnaris outbreaks during spring 2010 to summer 2012 and determined to be of
genomovar II (Mohammed and Arias 2014 ).
Fla. columnare may display Rhizoidal and Rough colony morphotypes, which
are associated with virulence and resistance to starvation/bacteriophages, respectively (Zhang et al. 2014 ). The Rough colonies may arise spontaneously, or are
induced by infection with bacteriophages, and have been demonstrated to be more
susceptible to predation by amoebae and ciliates, and produced more biofi lm (in the
presence of amoebae) (Zhang et al. 2014 ). A third morphotype has been described
as “Soft” (Laanto et al. 2014 ). By electron microscopy, the cells of Rhizoid and Soft
but not so Rough morphotypes displayed an organised structure, which may be
related to gliding motility; a refl ection of virulence properties. Planktonic cells of
the Rhizoid and Rough but not Soft colonies produced large membrane vesicles that
contained two proteins, i.e. OmpA and SprF, and may be associated with adhesion
and possibly invasion, and gliding motility, respectively. Also, the Rhizoid morphotype secreted a small, unidentifi ed 13 kDa protein, possibly related to virulence
(Laanto et al. 2014 ).
Diagnosis
Phenotypic Methods A simplistic approach has involved the observation of wet
preparations, prepared from lesion material, which were supposed to demonstrate
the presence of ‘column’ – like masses of bacteria (Snieszko 1958b ).
7 Flavobacteria and Cytophagas