Unfortunately the work has been rendered more difficult by the complexity of

Unfortunately the work has been rendered more

This preview shows page 322 - 324 out of 594 pages.

numerous investigations. Unfortunately, the work has been rendered more difficult by the complexity of the substance(s), which, at present, is known to include an ADP-ribosyltransferase toxin (AexT) (Braun et al., 2002), acetylcholinesterase (an
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Pathogenicity 303 ichthyotoxin with neurotoxic activity; Perez et ai, 1998), several proteases, namely two metallo-proteases [i.e. the 37kDa leucine amino-peptidase and the 30kDa metallo-protease 3 (Arnesen and Eggset, 1999)], PI, GCAT, AsaPl, P2 metallo- gelatinase and a serine caseinase (Gudmundsdottir et al, 1999), phospholipase, haemolysins and a leucocidin (Munro et al, 1980; Sheeran and Smith, 1981; Shieh and MacLean, 1975; Titball and Munn, 1981; Cipriano et al, 1981; Fuller et al, 1977; Rockey et aL, 1988; Huntly et aL, 1992; Lygren et aL, 1998), as well as LPS. Work with monoclonal antibodies has shown heterogeneity in the LPS (Rockey et ai, 1991). Elhs et <2/. (1981) reported that ECP of the pathogen, prepared by a cellophane overlay method, reproduced the lesions normally associated with the chronic form of furunculosis, e.g. muscle necrosis and oedematous swelHng 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 fish (Munro et al, 1980). In preparations offish cells, the ECP exhibited cytotoxic effects, and at higher concentrations was leucocytolytic and haemolytic. These investigators con- cluded 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 reproduces 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 fish, although their activities varied according to the nature of the fish species used. Thus, mortahties, accompanied by haemorrhaging at the vent and fins, and inflammation 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 fins, injection site and in the mouth; however, the majority of fish administered with this fraction survived. In contrast, rainbow trout were relatively resistant to the
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