411
media have been formulated for the selective recovery of the pathogen (Fijan 1969 ).
On this medium, the pathogen produces characteristically yellow-orange pigmented
colonies.
Characteristics of the Pathogen
The taxonomic status of the pathogen has undergone radical change since the
pioneering work of Davis ( 1922 ). Davis coined the name Bacillus columnaris
because, in wet preparations of infected material, the bacteria congregated in
column- like masses. According to Ordal and Rucker ( 1944 ), pure cultures of the
organism exhibited gliding, and therefore should be associated with the myxobacteria. The taxonomy became further complicated by the observation in cultures of
oval and spherical structures, which were thought to be microcysts (this notion was
subsequently rejected). This led to a re-classifi cation, as Chondrococcus columnaris. Shortly afterwards, Garnjobst ( 1945 ) suggested that the pathogen was actually
a Cytophaga, and thus, the transition was made to Cytophaga columnaris. With
further deliberation, the organism was transferred to Flexibacter, as Flexibacter
columnaris (Leadbetter 1974 ), and from phylogenetic data as Fla. columnare
(Bernardet et al. 1996 ).
Box 7.8: Flavobacterium columnare
Colonies appear to be fl at, spreading, yellowish green (fl exirubin-type pigment), with rhizoidal edges, and contain slender, strictly aerobic, Gramnegative rods of 4–8 × 0.5–0.7 μm in size, which move by gliding. Catalase,
H 2 S and oxidase are produced, but not indole, or lysine or ornithine decarboxylase. Nitrates are reduced. The methyl red test and Voges Proskauer reaction
are negative. Casein, gelatin and tributyrin are degraded, but not aesculin,
agar, cellulose, chitin, starch and tyrosine. Growth occurs at 4–30 °C (some
isolates grow also at 37 °C), and in 0–0.5 % (w/v), but not 1 % (w/v), sodium
chloride (Bernardet 1989 ; Bernardet and Grimont 1989 ; Bernardet et al.
1996 ). Dead bacterial cells, notably Esch. coli are lysed. Carbohydrates are
generally not utilised. Moreover, acid is not produced from arabinose, cellobiose, glucose, lactose, mannitol, raffi nose, salicin, sucrose or xylose. The
G + C ratio of the DNA is 32.9–35.9 moles % (Wakabayashi and Egusa 1966 ;
Pacha and Porter 1968 ; Pacha and Ordal 1970 ; Chun 1975 ; Bootsma and
Clerx 1976 ; Morrison et al. 1981 ). Four major serological groups and one
miscellaneous group have been recognised among the 325 strains examined
by Anacker and Ordal ( 1959 ). Moreover, separate and distinct DNA homology groups have been described (Song et al. 1988 ). Two major genetic groups
were recognised by PFGE using MluI restriction enzyme digestion among 30
isolates from channel catfi sh in the USA (Soto et al. 2007 ).
Flavobacterium columnare (=Flexibacter/Cytophaga columnaris)
media have been formulated for the selective recovery of the pathogen (Fijan 1969 ).
On this medium, the pathogen produces characteristically yellow-orange pigmented
colonies.
Characteristics of the Pathogen
The taxonomic status of the pathogen has undergone radical change since the
pioneering work of Davis ( 1922 ). Davis coined the name Bacillus columnaris
because, in wet preparations of infected material, the bacteria congregated in
column- like masses. According to Ordal and Rucker ( 1944 ), pure cultures of the
organism exhibited gliding, and therefore should be associated with the myxobacteria. The taxonomy became further complicated by the observation in cultures of
oval and spherical structures, which were thought to be microcysts (this notion was
subsequently rejected). This led to a re-classifi cation, as Chondrococcus columnaris. Shortly afterwards, Garnjobst ( 1945 ) suggested that the pathogen was actually
a Cytophaga, and thus, the transition was made to Cytophaga columnaris. With
further deliberation, the organism was transferred to Flexibacter, as Flexibacter
columnaris (Leadbetter 1974 ), and from phylogenetic data as Fla. columnare
(Bernardet et al. 1996 ).
Box 7.8: Flavobacterium columnare
Colonies appear to be fl at, spreading, yellowish green (fl exirubin-type pigment), with rhizoidal edges, and contain slender, strictly aerobic, Gramnegative rods of 4–8 × 0.5–0.7 μm in size, which move by gliding. Catalase,
H 2 S and oxidase are produced, but not indole, or lysine or ornithine decarboxylase. Nitrates are reduced. The methyl red test and Voges Proskauer reaction
are negative. Casein, gelatin and tributyrin are degraded, but not aesculin,
agar, cellulose, chitin, starch and tyrosine. Growth occurs at 4–30 °C (some
isolates grow also at 37 °C), and in 0–0.5 % (w/v), but not 1 % (w/v), sodium
chloride (Bernardet 1989 ; Bernardet and Grimont 1989 ; Bernardet et al.
1996 ). Dead bacterial cells, notably Esch. coli are lysed. Carbohydrates are
generally not utilised. Moreover, acid is not produced from arabinose, cellobiose, glucose, lactose, mannitol, raffi nose, salicin, sucrose or xylose. The
G + C ratio of the DNA is 32.9–35.9 moles % (Wakabayashi and Egusa 1966 ;
Pacha and Porter 1968 ; Pacha and Ordal 1970 ; Chun 1975 ; Bootsma and
Clerx 1976 ; Morrison et al. 1981 ). Four major serological groups and one
miscellaneous group have been recognised among the 325 strains examined
by Anacker and Ordal ( 1959 ). Moreover, separate and distinct DNA homology groups have been described (Song et al. 1988 ). Two major genetic groups
were recognised by PFGE using MluI restriction enzyme digestion among 30
isolates from channel catfi sh in the USA (Soto et al. 2007 ).
Flavobacterium columnare (=Flexibacter/Cytophaga columnaris)