336
Characteristics of the Pathogen
The organisms from fi sh match closely the description of Edw. tarda (Ewing et al.
1965 ; Cowan 1974 ; Farmer and McWhorter 1984 ), insofar as they are fairly reactive
(Table 6.1 ) Gram-negative rods, motile by means of peritrichous fl agella (Qin et al.
2014 reported nonmotile isolates from turbot in China). The original isolates of
Meyer and Bullock ( 1973 ) were identifi ed defi nitively as Edw. tarda by the
CDC. Thereafter, each successive report emphasised the similarity to the species
description of Ewing et al. ( 1965 ), highlighting the homogeneity of the fi sh isolates.
In fact, it is astonishing how little variation has been recorded in the phenotypic
characters; despite recovery from as far afi eld as Japan (Wakabayashi and Egusa
1973 ; Nakatsugawa 1983 ) and the USA (Amandi et al. 1982 ). The only difference
refl ects serology. Thus, four serotypes (A, B, C and D) have been recognised from
O-agglutination analyses of 270/445 isolates recovered from eel ponds in Japan during 1980 and 1981 (Park et al. 1983 ). Among the cultures, serotype B predominated
(22–35 % of the total), followed by serotype A (13–17 % of the isolates), serotype C
(4–13 % of the isolates) and serotype D (2–4 % of the total). Most of the isolates in
serotype A were derived from kidney samples. Moreover, this group was by far the
most virulent as assessed from experimental infections of eels, loach and tilapia
(Park et al. 1983 ) and natural outbreaks in Japanese fl ounder (Rashid et al. 1994a ,
b ). It has been argued that isolates from turbot in Spain constitute a separate serological group (Castro et al. 2006 ). Examination of genomic diversity by BOX-A1Rbased repetitive extragenic palindromic PCR (BOX-PCR) and PCR-ribotyping
recovered 51 isolates into 32 and 27 genotypes, respectively. These were correspondingly defi ned in 9 and 8 clusters (Maiti et al. 2008 ).
The G + C ratio of the DNA was calculated as 59 moles % (Amandi et al. 1982 ).
Confusion has enveloped the taxonomic status of this pathogen, insofar as the
‘Approved Lists of Bacterial Names’ (Skerman et al. 1980 ) include two specifi c
epithets for what is apparently the same organism, Edw. tarda and Edw. anguillimortifera. Edw. tarda was proposed initially by Ewing et al. ( 1965 ), and it would
appear that there was a lack of familiarity with the earlier work of Hoshina ( 1962 ),
who described Paracolobactrum anguillimortiferum. The characteristics of these
two nomenspecies are identical (Table 6.1 ). Recognising the efforts of Hoshina
( 1962 ), Sakazaki and Tamura ( 1975 ) proposed that Paracolobactrum anguillimortiferum should be reclassifi ed in the genus Edwardsiella , as Edw. anguillimortifera.
Furthermore, Sakazaki and Tamura ( 1975 ) emphasised that priority should be
attached to the specifi c epithet of anguillimortiferum rather than tarda . Thus two
names have resulted for what is surely the same organism. Clearly, this is an unacceptable situation and, despite the pioneering work of Hoshina ( 1962 ), it is our
contention that, to avoid further confusion in medical and veterinary microbiology,
the name of tarda should be retained.
6 Enterobacteriaceae Representatives
Characteristics of the Pathogen
The organisms from fi sh match closely the description of Edw. tarda (Ewing et al.
1965 ; Cowan 1974 ; Farmer and McWhorter 1984 ), insofar as they are fairly reactive
(Table 6.1 ) Gram-negative rods, motile by means of peritrichous fl agella (Qin et al.
2014 reported nonmotile isolates from turbot in China). The original isolates of
Meyer and Bullock ( 1973 ) were identifi ed defi nitively as Edw. tarda by the
CDC. Thereafter, each successive report emphasised the similarity to the species
description of Ewing et al. ( 1965 ), highlighting the homogeneity of the fi sh isolates.
In fact, it is astonishing how little variation has been recorded in the phenotypic
characters; despite recovery from as far afi eld as Japan (Wakabayashi and Egusa
1973 ; Nakatsugawa 1983 ) and the USA (Amandi et al. 1982 ). The only difference
refl ects serology. Thus, four serotypes (A, B, C and D) have been recognised from
O-agglutination analyses of 270/445 isolates recovered from eel ponds in Japan during 1980 and 1981 (Park et al. 1983 ). Among the cultures, serotype B predominated
(22–35 % of the total), followed by serotype A (13–17 % of the isolates), serotype C
(4–13 % of the isolates) and serotype D (2–4 % of the total). Most of the isolates in
serotype A were derived from kidney samples. Moreover, this group was by far the
most virulent as assessed from experimental infections of eels, loach and tilapia
(Park et al. 1983 ) and natural outbreaks in Japanese fl ounder (Rashid et al. 1994a ,
b ). It has been argued that isolates from turbot in Spain constitute a separate serological group (Castro et al. 2006 ). Examination of genomic diversity by BOX-A1Rbased repetitive extragenic palindromic PCR (BOX-PCR) and PCR-ribotyping
recovered 51 isolates into 32 and 27 genotypes, respectively. These were correspondingly defi ned in 9 and 8 clusters (Maiti et al. 2008 ).
The G + C ratio of the DNA was calculated as 59 moles % (Amandi et al. 1982 ).
Confusion has enveloped the taxonomic status of this pathogen, insofar as the
‘Approved Lists of Bacterial Names’ (Skerman et al. 1980 ) include two specifi c
epithets for what is apparently the same organism, Edw. tarda and Edw. anguillimortifera. Edw. tarda was proposed initially by Ewing et al. ( 1965 ), and it would
appear that there was a lack of familiarity with the earlier work of Hoshina ( 1962 ),
who described Paracolobactrum anguillimortiferum. The characteristics of these
two nomenspecies are identical (Table 6.1 ). Recognising the efforts of Hoshina
( 1962 ), Sakazaki and Tamura ( 1975 ) proposed that Paracolobactrum anguillimortiferum should be reclassifi ed in the genus Edwardsiella , as Edw. anguillimortifera.
Furthermore, Sakazaki and Tamura ( 1975 ) emphasised that priority should be
attached to the specifi c epithet of anguillimortiferum rather than tarda . Thus two
names have resulted for what is surely the same organism. Clearly, this is an unacceptable situation and, despite the pioneering work of Hoshina ( 1962 ), it is our
contention that, to avoid further confusion in medical and veterinary microbiology,
the name of tarda should be retained.
6 Enterobacteriaceae Representatives