272
oedematous swelling at the site of injection. This suggests that the toxins and
aggressins released by the bacteria in vivo are responsible for much of the pathology
of the disease. In addition, when injected intraperitoneally into rainbow trout, the
ECP proved to be fatal for the fi sh (Munro et al. 1980 ). In preparations of fi sh cells,
the ECP exhibited cytotoxic effects, and at higher concentrations was leucocytolytic
and haemolytic. These investigators concluded that most of the virulence factors
were produced extracellularly, with most strains of Aer. salmonicida producing
similar compounds, although the quantities varied. However, a detailed chemical
analysis was not carried out.
Other studies have also indicated that injection of ECP closely reproduce the
pathological condition attributed to furunculosis (Sakai 1977 ; Cipriano et al. 1981 ).
Cipriano et al. ( 1981 ) attempted to determine the role between ECP and virulence
by extracting the compounds from culture supernatants. The ECP was resolved into
four fractions by ion-exchange chromatography. It was deduced that fraction II possessed leucocytolytic activity, although this fraction was not associated with virulence. Rather, a link between virulence and the toxicity of crude material, and
fractions II and III, to cultured rainbow trout was observed. In this experiment, the
extracted material from virulent isolates was more toxic to tissue culture cells than
preparations derived from the avirulent strains. Fraction II also demonstrated proteolytic activity. Furthermore, results of in vivo toxicity studies revealed that three
of the fractions were toxic to fi sh, although their activities varied according to the
nature of the fi sh species used. Thus, mortalities, accompanied by haemorrhaging at
the vent and fi ns, and infl ammation at the site of injection, occurred in Atlantic
salmon and brook trout that received fractions I and II. Fraction III also caused
haemorrhaging at the base of the fi ns, injection site, and in the mouth; however, the
majority of fi sh administered with this fraction survived. In contrast, rainbow trout
were relatively resistant to the effects of all four fractions, insofar as no mortalities
resulted. However, administration of fraction II resulted in the development of characteristic furuncle-like lesions at the inoculation site. Fractions I, III and IV did not
cause any obvious pathology. The results of Cipriano et al. ( 1981 ) supported the
previous fi ndings of Sakai ( 1977 ) who, on the basis of work with crude ECP preparations, considered that a protease was the most pathogenic substance produced by
Aer. salmonicida. The effects ascribed to proteolytic activity by Sakai ( 1977 ) were
analogous to those noted by Cipriano et al. ( 1981 ) for fraction II. In fact, the muscle
necrosis and degeneration of connective tissue associated with furunculosis indicates proteolytic enzyme activity. Yet, Fyfe et al. ( 1986 ) recorded that protease
preparations were less effective than equivalent amounts of ECP (with similar
amount of proteolytic activity) at causing lesions, i.e. furuncles, following i.m.
injection of juvenile Atlantic salmon. This team identifi ed three major components
with molecular weights of 70 kDa (a serine protease; Ellis et al. 1997 ), 56 kDa (a
haemolysin) and 100 kDa (unidentifi ed protein) in the ECP (Fyfe et al. 1987a ); the
fi rst mentioned of which was produced in greater quantities after incubation for 18 h
at 25 °C compared to 125 h at 10 °C (Fyfe et al. 1987b ). Haemolysin production was
similar at both temperatures, but ten-fold more of the 100 kDa protein was produced
at the lower temperature.
5 Aeromonadaceae Representative (Aeromonas salmonicida)
oedematous swelling at the site of injection. This suggests that the toxins and
aggressins released by the bacteria in vivo are responsible for much of the pathology
of the disease. In addition, when injected intraperitoneally into rainbow trout, the
ECP proved to be fatal for the fi sh (Munro et al. 1980 ). In preparations of fi sh cells,
the ECP exhibited cytotoxic effects, and at higher concentrations was leucocytolytic
and haemolytic. These investigators concluded that most of the virulence factors
were produced extracellularly, with most strains of Aer. salmonicida producing
similar compounds, although the quantities varied. However, a detailed chemical
analysis was not carried out.
Other studies have also indicated that injection of ECP closely reproduce the
pathological condition attributed to furunculosis (Sakai 1977 ; Cipriano et al. 1981 ).
Cipriano et al. ( 1981 ) attempted to determine the role between ECP and virulence
by extracting the compounds from culture supernatants. The ECP was resolved into
four fractions by ion-exchange chromatography. It was deduced that fraction II possessed leucocytolytic activity, although this fraction was not associated with virulence. Rather, a link between virulence and the toxicity of crude material, and
fractions II and III, to cultured rainbow trout was observed. In this experiment, the
extracted material from virulent isolates was more toxic to tissue culture cells than
preparations derived from the avirulent strains. Fraction II also demonstrated proteolytic activity. Furthermore, results of in vivo toxicity studies revealed that three
of the fractions were toxic to fi sh, although their activities varied according to the
nature of the fi sh species used. Thus, mortalities, accompanied by haemorrhaging at
the vent and fi ns, and infl ammation at the site of injection, occurred in Atlantic
salmon and brook trout that received fractions I and II. Fraction III also caused
haemorrhaging at the base of the fi ns, injection site, and in the mouth; however, the
majority of fi sh administered with this fraction survived. In contrast, rainbow trout
were relatively resistant to the effects of all four fractions, insofar as no mortalities
resulted. However, administration of fraction II resulted in the development of characteristic furuncle-like lesions at the inoculation site. Fractions I, III and IV did not
cause any obvious pathology. The results of Cipriano et al. ( 1981 ) supported the
previous fi ndings of Sakai ( 1977 ) who, on the basis of work with crude ECP preparations, considered that a protease was the most pathogenic substance produced by
Aer. salmonicida. The effects ascribed to proteolytic activity by Sakai ( 1977 ) were
analogous to those noted by Cipriano et al. ( 1981 ) for fraction II. In fact, the muscle
necrosis and degeneration of connective tissue associated with furunculosis indicates proteolytic enzyme activity. Yet, Fyfe et al. ( 1986 ) recorded that protease
preparations were less effective than equivalent amounts of ECP (with similar
amount of proteolytic activity) at causing lesions, i.e. furuncles, following i.m.
injection of juvenile Atlantic salmon. This team identifi ed three major components
with molecular weights of 70 kDa (a serine protease; Ellis et al. 1997 ), 56 kDa (a
haemolysin) and 100 kDa (unidentifi ed protein) in the ECP (Fyfe et al. 1987a ); the
fi rst mentioned of which was produced in greater quantities after incubation for 18 h
at 25 °C compared to 125 h at 10 °C (Fyfe et al. 1987b ). Haemolysin production was
similar at both temperatures, but ten-fold more of the 100 kDa protein was produced
at the lower temperature.
5 Aeromonadaceae Representative (Aeromonas salmonicida)