327
Isolation
Isolation has been readily achieved from kidney, liver, spleen, intestine, brain and
skin or muscle lesions by inoculation of material into BHIA or blood agar. Following
incubation at 26 °C for 48 h, smooth circular (2 mm diameter), slightly convex,
entire, non-pigmented colonies develop (Hawke 1979 ). A selective medium has
been described by Shotts and Waltman ( 1990 ) [Appendix in Chap. 12 ].
Characteristics of the Pathogen
All the published reports point to the presence of a very homogeneous group of
bacteria phenotypically, including use of isozyme analysis (Starliper et al. 1988 ;
Bader et al. 1998 ), although subgroups may be recognised by molecular methods.
Thus, Bader et al. ( 1998 ) recognised 4 subgroupings among 20 isolates by use of
arbitrary primed PCR. Using AFLP, a single clone of Japanese isolates from ayu
was recognised, suggesting a single point source of origin of the organism [in Japan]
(Sakai et al. 2009 ).
Similarities have been observed with Edw. tarda, except that isolates of Edw.
ictaluri did not produce H 2 S or indole, or ferment glucose with the production of
gas at 37 °C. Moreover, the isolates did not agglutinate with antiserum to Edw. tarda
(Hawke 1979 ). However, in terms of DNA relatedness, the causal agent of enteric
Box 6.3: Edwardsiella ictaluri
Cultures comprise Gram-negative rod-shaped fermentative organisms (strains
with a limited tolerance for oxygen have been recovered from channel catfi sh
in the USA; Mitchell and Goodwin 2000 ), which are motile by peritrichous
fl agella. Catalase, ß-galactosidase (a variable response has been recorded
between various laboratories) and lysine and ornithine decarboxylase are produced but not H 2 S, indole, oxidase or phenylalanine deaminase. The methyl
red test is positive, but not so the Voges Proskauer reaction. Nitrates are
reduced. Growth occurs in 1.5 % but not 2 % (w/v) sodium chloride. The optimum growth temperature is between 20 and 30 °C, which coincides with the
water temperature during severe outbreaks of the disease. Blood is degraded,
but not casein, DNA, elastin, gelatin, Tween 20, 40, 60 and 80 or urea. Acid is
produced from fructose, galactose, glycerol, maltose, mannose and ribose but
not from adonitol, aesculin, amygdalin, arabinose, arbutin, cellobiose, dulcitol, erythritol, inositol, inulin, lactose, melezitose, raffi nose, rhamnose, salicin, sodium malonate, sorbitol, sorbose, starch or sucrose (Waltman and
Shotts 1986a ). The G + C ratio of the DNA is 53 moles % (Hawke et al. 1981 ).
The complete genome sequence of strain 93–146, which was recovered from
an outbreak of disease in Louisiana, USA in 1993, was 3812315 bp with 3783
predicted protein coding genes (Williams et al. 2012 ).
Edwardsiella ictaluri
Isolation
Isolation has been readily achieved from kidney, liver, spleen, intestine, brain and
skin or muscle lesions by inoculation of material into BHIA or blood agar. Following
incubation at 26 °C for 48 h, smooth circular (2 mm diameter), slightly convex,
entire, non-pigmented colonies develop (Hawke 1979 ). A selective medium has
been described by Shotts and Waltman ( 1990 ) [Appendix in Chap. 12 ].
Characteristics of the Pathogen
All the published reports point to the presence of a very homogeneous group of
bacteria phenotypically, including use of isozyme analysis (Starliper et al. 1988 ;
Bader et al. 1998 ), although subgroups may be recognised by molecular methods.
Thus, Bader et al. ( 1998 ) recognised 4 subgroupings among 20 isolates by use of
arbitrary primed PCR. Using AFLP, a single clone of Japanese isolates from ayu
was recognised, suggesting a single point source of origin of the organism [in Japan]
(Sakai et al. 2009 ).
Similarities have been observed with Edw. tarda, except that isolates of Edw.
ictaluri did not produce H 2 S or indole, or ferment glucose with the production of
gas at 37 °C. Moreover, the isolates did not agglutinate with antiserum to Edw. tarda
(Hawke 1979 ). However, in terms of DNA relatedness, the causal agent of enteric
Box 6.3: Edwardsiella ictaluri
Cultures comprise Gram-negative rod-shaped fermentative organisms (strains
with a limited tolerance for oxygen have been recovered from channel catfi sh
in the USA; Mitchell and Goodwin 2000 ), which are motile by peritrichous
fl agella. Catalase, ß-galactosidase (a variable response has been recorded
between various laboratories) and lysine and ornithine decarboxylase are produced but not H 2 S, indole, oxidase or phenylalanine deaminase. The methyl
red test is positive, but not so the Voges Proskauer reaction. Nitrates are
reduced. Growth occurs in 1.5 % but not 2 % (w/v) sodium chloride. The optimum growth temperature is between 20 and 30 °C, which coincides with the
water temperature during severe outbreaks of the disease. Blood is degraded,
but not casein, DNA, elastin, gelatin, Tween 20, 40, 60 and 80 or urea. Acid is
produced from fructose, galactose, glycerol, maltose, mannose and ribose but
not from adonitol, aesculin, amygdalin, arabinose, arbutin, cellobiose, dulcitol, erythritol, inositol, inulin, lactose, melezitose, raffi nose, rhamnose, salicin, sodium malonate, sorbitol, sorbose, starch or sucrose (Waltman and
Shotts 1986a ). The G + C ratio of the DNA is 53 moles % (Hawke et al. 1981 ).
The complete genome sequence of strain 93–146, which was recovered from
an outbreak of disease in Louisiana, USA in 1993, was 3812315 bp with 3783
predicted protein coding genes (Williams et al. 2012 ).
Edwardsiella ictaluri