1990 described plasmids of 28 34 21 and 61 mDa from isolates recovered from

1990 described plasmids of 28 34 21 and 61 mda from

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(1990) described plasmids of 2.8, 3.4, 21 and 61 mDa from isolates recovered from Atlantic salmon and cod. These authors reported 11 plasmid profiles for V. salmo- nicida. A similar plasmid composition has been indicated for isolates from the Faroe Islands (Nielsen and Dalsgaard, 1991). Comparing isolates from Canada, the Faroe Islands, Norway and Shetland, S0rum et al. (1993a) noted a similarity in plasmid profile, with three plasmids of 2.8, 3.4 and 21 mDa revealed. Furthermore, a con- clusion has been reached that all strains carry plasmids (Valla et al, 1992). Differ- ences have also been implied by serological studies, which have indicated the presence of two serotypes. DNA hybridisation of four cultures confirmed homogeneity (DNA homo- logy =82-100%), but low relatedness to V. anguillarum (30%), V. ordalii (34%) or V. parahaemolyticus (40%) (Wiik and Egidius, 1986). Although these data were used to justify the uniqueness of V. salmonicida, the relationship to other representatives of the Vibrionaceae was not considered. The vaHdity of the species is not, however, questioned, and in the detailed study of Austin et al. (1997) V. salmonicida formed a discrete taxon among the other fish-pathogenic vibrios. V. splendidus A detailed taxonomic study by Austin et al. (1997) of 22 isolates revealed that fish- pathogenic isolates (these were non-pathogenic in laboratory-based infectivity experi- ments with Atlantic salmon and rainbow trout) were markedly heterogeneous, being recovered in 7 ribotype clusters, many API 20E profiles and 6 BIOLOG-GN groups (the type strain was recovered as a single-member cluster). However, only two serogroups (there were some cross-reactions with V. pelagius antiserum) and one LPS profile was recognised. With such heterogeneity, it is difficult to decide whether or not any fish isolates actually constitute bona fide V. splendidus. Notwithstanding, an attempt will be made to present a consensus view of the phenotypic traits associated with so-called V. splendidus:
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146 Bacterial Fish Pathogens Vibrio splendidus Cultures contain motile, fermentative, Gram-negative rods, which produce argi- nine dihydrolase (some isolates), catalase, P-galactosidase, lysine decarboxylase and oxidase, but not H2S, indole, ornithine decarboxylase or phenylalanine de- aminase, degrade blood (P-haemolysis), chitin, gelatin, Hpids and starch, but not aesculin or urea, reduce nitrates, demonstrate positivity for the methyl red test, but not the Voges Proskauer reaction, are sensitive to the vibriostatic agent, 0/129, grow at 37°C and in 3% (w/v), but not 0 or 7% (w/v), sodium chloride, utilise citrate, P-gentiobiose, glucose, ribose and sorbitol, but not malonate or sucrose, and produce acid from glucose (no gas), maltose and mannose, but not from arabinose, inositol, mannitol, sorbitol or sucrose. The G + C ratio of the DNA is 45.7-47.8 mol % (Jensen et al, 2003).
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