Rev. sci. tech. Off. int. Epiz.,
1984, 3 (3), 597-609.
Cultural, biochemical and serological
characteristics of bacterial isolates
from carp erythrodermatitis in Hungary
J.F. SÖVÉNYI*, D.G. ELLIOTT**, Gy. CSABA***,
J. OLÁH**** and J.J. MAJNARICH*****
Summary : Biochemical and serological properties and antibiotic sensi­
tivity patterns for nine bacterial isolates from common carp (Cyprinus
carpio L.) with carp erythrodermatitis in Hungary were studied. Also
included were two other bacterial isolates from similar cyprinid fish
ulcerative diseases — an unidentified bacterium from a crucian carp
(Carassius carassius L.) in Hungary and an atypical Aeromonas salmonicida strain from a goldfish (Carassius auratus L.J in the United Sta­
tes. The carp erythrodermatitis isolates and the crucian carp isolate
showed uniform biochemical reactions and were considered identical.
These isolates could be distinguished from the goldfish A. salmonicida
isolate by negative reactions in catalase and indole production tests;
positive reactions in gelatinose and acetoin production tests; and failure
to catabolize glycerol, mannitol and sucrose. Several phehotypic cha­
racteristics distinguished the carp erythrodermatitis isolates from each
of the presently proposed subspecies of A. salmonicida. Antibiograms
for all the bacterial strains tested showed few differences.
Standard immunoelectrophoresis techniques revealed as many as
five common antigens in most of the bacterial isolates. One antigen was
lacking in one of the carp erythrodermatitis isolates and in the goldfish
isolate. Line immunoelectrophoresis allowed direct comparison and
identification of the antigens from different isolates. Since results of
the serological study were preliminary, additional research is needed to
better define the serological relationship among carp erythrodermatitis
isolates and various strains of A. salmonicida.
INTRODUCTION
The economic importance of furunculosis in salmonid fishes has resulted
in numerous studies of the causative bacterium, Aeromonas
salmonicida,
* Veterinary Research Institute of the Hungarian Academy of Sciences, Budapest,
Hungary.
** School of Fisheries, University of Washington, Seattle, Washington, U S A .
*** National Veterinary Center, Budapest, Hungary.
**** Fisheries Research Institute, Szarvas, Hungary.
***** Director, BioMed Research Laboratories Inc., Seattle, Washington, U S A .
— 598 —
since the end of the 19th century. Early investigations were concerned with
bacterial isolates which possessed characteristic properties with respect to
disease manifestations in fish and reactions in biochemical test media. The
taxon A. salmonicida
subspecies salmonicida
has been proposed for such
strains (24, 4). Recently, however, many reports have been published on A.
salmonicida
infections in non-salmonid fishes, particularly cyprinids. The
bacterial isolates from these outbreaks often induce unusual patterns of
disease and exhibit atypical biochemical reactions.
Development of warm-water carp breeding in E u r o p e has brought an
awareness of carp diseases during the last decade. Following Fijan's (8) des­
cription of carp erythrodermatitis (CE) in Cyprinus carpio (L.), research on
this disease revealed an atypical variant of A. salmonicida in the skin ulcers
of affected carp (3). Study of bacterial isolates from Hungarian carp with CE
began in 1975; research results have indicated that these isolates also are
related to A. salmonicida (5).
Taxonomic categorization of non-salmonid A. salmonicida strains on the
basis of biochemical properties has not been completely satisfactory. It
appears that the proposed taxa A salmonicida subspecies achromogenes
and
A. salmonicida subspecies masoucida (14, 24, 4), which include isolates that
fail to produce soluble brown pigment on tryptic digest media, may not be
appropriate for the majority of the non-salmonid isolates. For this reason a
new taxon, A. salmonicida
subspecies nova, has been suggested for nonsalmonid strains (20). There are still difficulties in assigning some of the des­
cribed isolates to any of the proposed categories, however, and published
information on the biochemical characteristics of some isolates, such as those
from carp, is limited.
Several authors have conducted serological analyses of thermostable and
thermolabile antigens of A. salmonicida and generally have demonstrated a
high degree of homogeneity among the strains studied. Karlsson (13) investig­
ated thermostable and thermolabile antigens of 12 A salmonicida strains by
double immunodiffusion and agglutination techniques and detected no
differences. Similar results were obtained by Popoff (23) who studied
thermostable antigens of 39 « typical » A. salmonicida
isolates by crossabsorption and agglutination. Kimura (14) compared thermostable and ther­
molabile somatic antigens of an atypical isolate (assigned to A.
salmonicida
subspecies masoucida) with those of « typical » A. salmonicida by double
cross-absorption procedures and found an additional thermolabile compo­
nent in the atypical isolate. McCarthy and Rawle (19) employed passive
haemagglutination tests and showed strong cross-reactions of A.
salmonicida
antisera with thermostable antigens of six A. salmonicida
strains, but no
cross-reaction with thermostable antigens of A. hydrophila,
Pseudomonas
fluorescens and Vibrio anguillarum. A later report by McCarthy and Roberts
(20) indicated that weak cross-reactions occurred between A. hydrophila anti­
gens and three of six A. salmonicida antisera used. There are n o reports
concerning serological reactions of thermostable or thermolabile cellular
antigens of A. salmonicida strains from E u r o p e a n cultured carp.
— 599 —
The purpose of the present investigation was to characterize C E bacterial
isolates from H u n g a r i a n c o m m o n carp (Cyprinus carpio L.) with respect to
cultural, biochemical and serological properties. For comparative purposes,
two n o n - C E isolates obtained from skin ulcers of cyprinid fish — one from a
crucian carp (Carassius carassius L.) in H u n g a r y and the other from a gold­
fish (Carassius auratus L.) in the United States — were included in the
research.
MATERIALS A N D METHODS
Nine bacterial isolates were obtained from c o m m o n carp with C E and one
isolate (CC) was cultured from a skin ulcer of a crucian carp at a H u n g a r i a n
aquaculture facility. The m e t h o d of isolation was described by Csaba et al.
(5). Isolates 109-112 and C C were cultured from fish in 1981, while the
remaining H u n g a r i a n isolates were collected during the spring of 1982. All
isolates were stored in tubes of semi-solid tryptose serum medium (described
below) at 4 ° C and subcultured every two m o n t h s . The goldfish isolate (G)
originated from fish at a hatchery in the midwestern United States (isolate 1)
(6) and had been stored lyophilized prior to this study. This isolate h a d been
identified as an atypical strain of A. salmonicida, and its biochemical charac­
teristics were consistent with those for the proposed taxon A.
salmonicida
subspecies nova (25).
Except where otherwise noted, the goldfish isolate was cultured at 27°C
on trypticase soy agar (BBL Microbiology Systems, Cockeysville, Maryland,
USA). The other isolates (including CC) were cultured on plates containing
1% tryptose (Difco Laboratories, Detroit, Michigan, U S A ) , 10% inactivated
horse serum (Oxoid U S A Inc., Columbia, Maryland) and 1.1% agar (Difco).
Bacterial isolates were characterized by conventional cultural and bio­
chemical tests (7). Reactions were monitored for five days after inoculation.
Antibiograms of the strains were obtained on Mueller-Hinton plates
(Difco) using « Resistest » discs ( H u m a n Inoculum Producing and Research
Institute, Gödöllö-Budapest, H u n g a r y ) . The antibiotic content of the discs is
shown in Table II. Bacterial lawns were prepared and antibiotic discs were
applied according to standard Kirby-Bauer techniques (1). Plates were incub­
ated at 27°C for three days.
Soluble thermostable antigens for immunoelectrophoresis and passive
haemagglutination tests were prepared from 3-day-old cultures by alkaline
hydrolysis, using a method modified from that of Macpherson et al. (16). A
20 mg sample of bacteria was removed carefully from the plates, rinsed three
times in p H 7.2 p h o s p h a t e buffered saline (PBS), and suspended in 5 ml of
PBS at p H 11. The suspension was incubated in a 100°C water bath for 1 h,
then centrifuged at 1400 g for 10 min. The absorbance of the supernatant
fluid was adjusted to 1.3 at a wavelength of 270 n m . After 24 hrs. dialysation
— 600 —
with 20 volumes of p H 7.2 PBS at 4 ° C , the supernatant fluids were stored at
- 2 0 ° C and used as antigen solutions.
The C C and G isolates were used for preparation of antisera in rabbits.
New Zealand albino rabbits weighing approximately 1 kg each were
immunized with five injections of formalin-killed bacterial cells (20 mg
cells/ml PBS). A minimum of two rabbits was used for each antigen. The
injection schedule was as follows : day 1, 0.1 ml killed cells intravenously;
day 2, 0.2 ml killed cells intravenously; day 3, 0.5 ml killed cells intra­
venously; day 8, 1.5 ml killed cells intraperitoneally; day 12, 1 ml killed cells
intravenously; day 32, 0.1 ml live cells intradermally. The animals were bled
on day 42.
The IgG fraction was obtained from rabbit serum by salt fractionation
with N a S 0 according to a method similar to that of Williams and Chase
(29). The serum was mixed with an equal volume of 3 0 % N a S 0 for
20 minutes at r o o m temperature. The mixture was centrifuged at 6000 g for
10 min, and the pellet was washed twice with 14% N a S 0 . The pellet was
then dissolved in a small a m o u n t of PBS containing 0.02% sodium azide at
4 ° C . Antibody solutions were stored at - 2 0 ° C .
2
4
2
2
4
4
For passive haemagglutination tests with whole serum, sheep red blood
cells were preserved with pyruvic aldehyde as described by Hirata and Brandriss (11). Adsorption of antigen to the red blood cells was achieved by
incubating a 1:10 (v/v) mixture of red blood cells and soluble antigen at 37°C
for 30 min. The cells were then washed five times in PBS and mixed with PBS
to give a final cell suspension of 0 . 5 % . Titration on Takátsy-type microtitre
plates was done according to standard procedures (10).
Double immunodiffusion and immunoelectrophoresis procedures were
performed on slides coated with 1% agarose in barbital buffer (pH 8.6, ionic
strength 0.1) (27). T w o immunoelectrophoresis techniques, standard immu­
noelectrophoresis (21) and line immunoelectrophoresis (15) were used. All
antigens were tested with b o t h anti-CC and anti-G antibodies. For standard
immunoelectrophoresis, 0.5 µl of soluble antigen was placed in each of two
wells on a slide (Fig. 1), and electrophoresis was carried out for 2 hrs. at
7 V / c m . Then, 0.1 ml of antibody solution was measured into the central
longitudinal slit in the gel. Slides were incubated at r o o m temperature for
2 days to allow precipitin lines to form. For line immunoelectrophoresis, the
antibody solution was incorporated into the gel by first mixing the solution
with an equal volume of barbital buffer and then adding 1% agarose. In the
centre of the slide, the antibody-containing gel was replaced by three rectan­
gular gel pieces containing antigen. The middle rectangle contained a refer­
ence antigen, while the other rectangles contained C E isolate antigens
(Fig. 2). CC antigen served as a reference when anti-CC antibody was used,
and G antigen served as a reference when anti-G antibody was used. Electro­
phoresis was run for 3 hrs. at 6.2 V / c m . For all tests, dried gels were stained
with Coomassie brilliant blue solution (21).
— 601
RESULTS
Growth of the C E and C C isolates was generally slower t h a n that of isol­
ate G, even when both were grown on tryptose serum medium. All isolates
produced friable, autoaggregating colonies on solid media, but only isolate G
produced soluble b r o w n pigment on tryptic digest medium. Biochemical test
results are presented in Table I. All bacteria tested were G r a m negative, n o n
motile rods which were oxidase-positive fermenters and failed to grow at
37°C (characteristics typical of A. salmonicida).
The C E and CC isolates,
unlike isolate G, produced acetoin and gelatinase, did not produce catalase or
indole, and were unable to ferment glycerol, mannitol or sucrose.
Antibiograms of the various isolates showed uniform resistance against
penicillin derivatives as well as lincomycin and vancomycin (Table II). Vari­
able effects were observed with polymyxin B, Colistin (polymyxin E) and
sumetrolim.
Soluble antigens of the C C and G isolates reacted with identical titres
(4096) when either anti-CC or anti-G serum was used in passive
haemagglutination tests. In addition, preliminary examination of soluble
antigens in double immunodiffusion tests showed at least three lines of iden­
tity among all of the antigen solutions when any of the antibody solutions
was used. Standard immunoelectrophoresis of the antigen solutions gave pat­
terns of as many as five precipitin lines as demonstrated in Fig. 1. Similar
precipitin lines were observed for all the isolates except for C E isolate 109,
which lacked the b line, and isolate G, which showed no e line with anti-CC
antibodies. N o antigens showed an e line when tested with anti-G antibodies.
Line immunoelectrophoresis resulted in as many as seven distinguishable
precipitin lines (Fig. 2). The leading edge of each precipitin line, except for
that of antigen VII, was blurred. Line VII did not occur in immunoelectro­
phoresis with anti-G antibodies. Line VII converged with line VI when antiCC antibodies were tested against C C antigens. Lines I and IV were absent
when antigen from isolate 109 was used.
DISCUSSION
Cultural characteristics of the bacterial isolates examined in this study
were the same as those described by others (5, 25). Biochemical testing reveal­
ed a striking homogeneity between the CE and C C isolates. Therefore, isolate
CC should be considered an isolate of the carp erythrodermatitis agent from
crucian carp. N o biochemical test results conflict with those published for
other CE isolates by Bootsma and Blommaert (3) and Csaba et al. (5),
although the present study represents a more extensive biochemical character­
ization of Hungarian isolates than that reported by Csaba et al. (5). A series
of 74 biochemical tests performed by Wiedemann (28) using 19 G e r m a n C E
isolates showed differences from H u n g a r i a n strains in four tests : esculin
— 602
TABLE 1
Comparison of cultural and biochemical
characteristics
of the carp erythrodermatitis
isolate, the crucian carp isolate
and the goldfish
isolate
Test or substrate
Gram stain
Growth at 37°C
Motility
Sensitivity to 0/129
Production of soluble brown pigment
on tryptic digest agar
Catalase
Oxidase (Kovács)
/3-haemolysis (bovine or sheep blood)
/3-galactosidase (ONPG)
Esculin hydrolysis
Arginine dihydrolase/decarboxylase
Lysine decarboxylase
Ornithine decarboxylase
Urease
Gelatinase
Nitrate reduction
Simmons citrate utilization
Acetoin production (Voges-Proskauer)
H S production
Indole production
Fermentation (glucose)
Acid production from :
adonitol
arabinose
dulcitol
glycerol
glucose
inositol
lactose
maltose
mannitol
raffinose
rhamnose
salicin
sorbitol
sucrose
trehalose
xylose
2
CE and CC
isolates
Goldfish
isolate
-
—
-—
+ (delayed)
-
+
+
+
+
+
-
-—
—
•
+
•
—
—
+
-
•
—
—
+
+
_
_
—
-
+
•
+
—
—
+
•
—
+
—
_
—
—
_
-
—
—
_
-
-
_
+
— 603 —
hydrolysis, H S production, citrate utilization and xylose catabolism tests
were negative for the H u n g a r i a n isolates. Some of the discrepancies m a y be
due to the use of different media for H S production and citrate utilization
tests.
2
2
The H u n g a r i a n C E isolates differ from isolate G with respect to several
reactions, including production of catalase, indole, acetoin and gelatinase;
and acid production from glycerol, mannitol and sucrose. These properties
separate the C E isolates from the proposed taxon A. salmonicida subspecies
nova (18).
Antibiotic
sensitivity
Antibiotics*
Ampicillin
Carbenicillin
Cephalosporin
Chloramphenicol
Chlortetracycline
Colistin
Erythromycin
Gentamicin
Kanamycin
Lincomycin
Methicillin
Nalidixic acid
Neomycin
Nitrofurantoin
Oxacillin
Oxytetracycline
Paramomycin
Penicillin
Polymyxin B
Pristinamycin
Spiramycin
Streptomycin
Sumetrolim
Tetracycline
Vancomycin
TABLE II
of carp erythrodermatitis
isolates, crucian carp
and goldfish ulcer disease isolate
isolate
Reactions of isolates
CC
109
110
111
112
113
114
R**
R
S
S
S
S
R
R
I
R
R
S
S
R
R
S
S
S
R
S
S
R
R
I
S
S
S
S
S
R
R
S
S
S
R
R
I
S
S
R
S
S
s
s
s
R
R
S
S
s
R
S
s
R
S
I
I
s
s
s
R
sS
s
s
s
s
s
S
S
I
S
R
R
S
R
R
S
s
s
R
s
s
R
S
R
R
S
I
I
I
S
I
R
S
s
R
S
s
s
s
s
s
R
s
R
R
S
S
s
R
S
s
s
s
sI
s
s
R
R
s
R
R
S
S
s
s
s
R
R
R
I
S
I
S
S
R
s
s
s
s
s
116
.. R
R
I
S
S
R
S
S
s
R
R
S
R
R
R
R
s
s S
s • Rs
R
s
s
s
R
S
S
R
S
I
S
I
R
S
I
I
I
R
I
R
S
I
R
R
I
I
I
R
I
R
sI
s
s
R
117
118
G
R
R
I
S
S
R
S
S
S
R
R
S
S
R
R
I
S
S
R
S
S
S
R
R
S
S
R
R
I
S
S
S
s
R
S
s
s
sI
s
sI
R
R
s
R
S
s
R
R
I
I
sS
s
R
s
s
s
R
R
S
R
S
R
S
S
R
R
S
I
S
s
s
R
* Antibiotic content of the discs : penicillin : 3 I U ; cephalosporin, erythromycin, lincomycin, oxacillin, pristi­
namycin : 10 mg; polymyxin B : 15 mg (93.75 I U ) ; ampicillin, Colistin, gentamicin, methicillin : 20 mg; sume­
trolim : 25 mg; chloramphenicol, Chlortetracycline, kanamycin, nalidixic acid, Oxytetracycline, spiramycin,
streptomycin, tetracycline : 30 mg; carbenicillin, paramomycin, vancomycin : 50 mg; neomycin : 100 mg;
nitrofurantoin : 300 mg.
** Symbols : S : sensitive; I : intermediate sensitivity; R : resistant; according t o the manufacturer's instruc­
tions.
— 604 —
Although the CE isolates do not produce pigment, they differ in some
reactions from the proposed type strain (NCMB 1110) for A.
salmonicida
subspecies achromogenes
(4). N C M B 1110 produces catalase and indole and
catabolizes sucrose and glycerol. The C E isolates also differ with respect to
the above reactions and several additional characteristics from the type strain
(Kimura 1-a-l) of another achromogenic A. salmonicida variant, the propos­
ed subspecies masoucida (4). The Kimura 1-a-l strain exhibits lysine decar­
boxylase activity, hydrolyzes esculin, produces H S and catabolizes mannitol.
2
When compared with the characteristics of atypical n o n - C E strains of A.
salmonicida studied by other authors (17, 18, 9, 26, 22, 25), the production
of gelatinase by C E isolates, their failure to produce catalase and indole, and
their inability to ferment mannitol and sucrose are consistent differences.
One atypical A. salmonicida isolate described from the roach (Rutilus rutilus
L.) by H u b b e r t and Williams (12) more closely resembles the C E isolates with
respect to biochemical reactions, but the roach isolate is catalase positive and
catabolizes sucrose. Thus, from our biochemical test results and those
published by others, it appears that the C E agent does not fit well into any of
the A. salmonicida taxa presently proposed, and that a new taxon m a y be
required to accommodate this bacterium. A numerical taxonomic analysis
FIG. 1
Standard immunoelectrophoresis
(electrophoresis followed by double diffusion)
Left : arrangement of antigen wells (circles) and serum well (longitudinal slit).
Right : appearance of precipitin lines.
— 605 —
and study of D N A homology and base pair ratios of C E « typical » and
« atypical » A. salmonicida
isolates may be necessary to resolve this ques­
tion.
The use of two immunoelectrophoresis techniques allowed the identific­
ation of both c o m m o n and unique thermostable antigens among the bacterial
isolates tested. Antigens from different isolates which appeared identical with
respect to electrophoretic mobility and antibody specificity in standard
immunoelectrophoresis tests were compared directly using line electro­
phoresis techniques. By these methods, antigen b (which extended from the
origin toward both the cathode and anode in standard immunoelectrophore­
sis tests) was determined to be equivalent to antigens I (which migrated
toward the cathode) and IV (which migrated toward the anode) of the line
immunoelectrophoresis tests, as all of these precipitin lines were absent in C E
isolate 109. Similarly, antigens e and VII were considered identical due to
electrophoretic mobility patterns and the fact that both were absent in tests
using the isolate G antigens and anti-G antibodies. Also, in comparison to
the CE isolates, the C C isolate possessed small a m o u n t s of antigen in both
the e and VII lines (as shown by weak staining of the e line and reduced dis-
FIG. 2
Line immunoelectrophoresis
Left : arrangement of antigen and antiserum areas. Dotted area : agarose contai­
ning antibodies; clear areas : samples windows with the reference antigen in the
middle window. Right : appearance of precipitin lines after electrophoresis of isolates
CC (as reference), 110 (left) and 111 (right) antigens.
— 606 —
tance from the origin of the line VII), a result supporting the conclusion that
these antigens were identical. Further analysis suggested that line a of the
standard immunoelectrophoresis tests was equivalent to lines II and III of
line immunoelectrophoresis, because these antigens exhibited little or no
charge at p H 8.6. Antigen c was most likely homologous to antigen VI
because these lines stained more intensely than any of the other precipitin
lines. Electrophoretic mobility patterns suggested that the remaining antigens, d and V, were also equivalent.
Although the preliminary analyses indicated a high degree of homogeneity among the thermostable antigens of the isolates tested (with the exception of single antigens absent from one CE isolate and isolate G), further
tests are needed to compare thermolabile antigens and to better characterize
the structure of the antigens tested. Additional experiments are also necessary
to determine antigenic relationships of CE isolates to « typical » salmonid A.
salmonicida and to other species in the genus
Aeromonas.
ACKNOWLEDGEMENTS
P a r t of this work was made possible through the efforts of Dr. J o h n E.
Halver of the University of Washington School of Fisheries. Dr. Halver
arranged a two-month scholarship for one of the authors ( J . F . Sòvényi) for
study at the School of Fisheries.
We thank Dr. J. Farkas, Fisheries Research Institute, Szarvas, Hungary,
for helpful consultation on bacteriological matters. We are also grateful to
Drs. Michael H . Schiewe and Harold O. Hodgins of the Northwest and
Alaska Fisheries Center, National Oceanic and Atmospheric Administration,
Seattle, Washington, for critical review of the manuscript.
*
* *
CARACTÈRES CULTURAUX, BIOCHIMIQUES ET SÉROLOGIQUES DE SOUCHES BACTÉRIENNES ISOLÉES DE CAS D'ÉRYTHRODERMATITE DE LA
CARPE EN HONGRIE. — J.F. Sövényi, D.G. Elliott, Gy. Csaba, J. Oláh et J.J.
Majnarich.
Résumé : L'étude porte sur neuf souches isolées en Hongrie de carpes
communes (Cyprinus carpio L.) atteintes d'érythrodermatite, et sur
deux autres souches : l'une, non identifiée, issue d'un carassin (Carassius carassius L.) présentant des lésions ulcéreuses en Hongrie, l'autre,
américaine, étant une souche atypique d'Aeromonas salmonicida provenant d'un cyprin doré (Carassius auratus L.) atteint également
d'ulcérations cutanées. Les souches d'érythrodermatite et celle du
carassin sont biochimiquement identiques. Elles se différencient de
celle du cyprin doré par leur absence de catalase et de production
d'indole et leur incapacité à utiliser le glycérol, le mannitol et le saccha-
— 607 —
rose. En revanche, elles possèdent une gélatinose et produisent de l'acétoine. Plusieurs caractères phénotypiques de ces souches ne cadrent pas
avec ceux définissant les sous-espèces de A. salmonicida actuellement
proposées. L'antibiosensibilité de toutes les souches ne présente que
peu de différences.
L'immunoélectrophorèse
(technique standard) démontre jusqu'à
cinq antigènes communs à la plupart des souches, mais l'un d'eux manque à la fois dans une des souches d'érythrodermatite et dans celle du
cyprin doré. D'un autre côté, la technique de migration électrophorétique des antigènes dans un gel contenant les anticorps permet de comparer et d'identifier directement les antigènes des différentes souches bactériennes. Ces résultats sont préliminaires et nécessitent d'autres travaux pour éclaircir la relation sérologique des germes étudiés avec A.
salmonicida.
CARACTERES CULTURALES, BIOQUÍMICOS Y SEROLÓGICOS DE CEPAS
BACTERIANAS AISLADAS DE CASOS DE ERITRODERMATITIS DE LA
CARPA EN HUNGRÍA. — J.F. Sövényi, D.G. Elliott, Gy. Csaba, J. Oláh y J.J.
Majnarich.
Resumen : Se refiere el estudio a nueve cepas aisladas en Hungría de
carpas comunes (Cyprinus carpio L.) atacadas de eritrodermatitis, y a
otras dos cepas : una sin identificar procedente de un carasio (Carassius carassius L.) con lesiones ulcerosas en Hungría, siendo la otra,
norteamericana, una cepa atipica de Aeromonas salmonicida procedente de un ciprino dorado (Carassius auratus L.) también afectado de
ulceraciones cutáneas. Las cepas de eritrodermatitis y la del carasio son
bioquímicamente idénticas. Se diferencian de la del ciprino dorado por
su falta de catalasis y de producción de indol y su incapacidad para utilizar el glicerol, el manitol y la sacarosa. En cambio, poseen una gelatinasa y producen acetoína. Varios caracteres fenotípicos de estas cepas
no encajan con los que definen las subespecies de A. salmonicida
actualmente propuestas. La antibiosensibilidad de todas las cepas presenta pocas diferencias.
La inmunoelectroforesis (técnica estándar) pone de manifiesto hasta
cinco antígenos comunes para la mayoría de las cepas, aunque uno de
ellos falta a la vez en una de las cepas de eritrodermatitis y en la del
cíprino dorado. Por otro lado, con la técnica de migración electroforética de los antígenos en un gel que contenga los anticuerpos, se pueden
comparar e identificar directamente los antígenos de las distintas cepas
bacterianas. Estos resultados son preliminares y requieren otras investigaciones para dilucidar la relación serológica de los gérmenes estudiados con A. salmonicida.
*
* *
— 608
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