There have been several reports of acid production in sucrose fermentation

There have been several reports of acid production in

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There have been several reports of acid production in sucrose fermentation tests among typical isolates (see Fryer et al, 1988; Wiklund et al, 1992). This is relevant because hitherto this was one of the tests used to differentiate typical from atypical isolates of the pathogen (Martin-Carnahan and Joseph, 2005). Plasmid profiles of Aeromonas salmonicida Plasmids carried by typical (14 strains) and atypical (11 strains) forms of Aer. salmonicida have also provided additional genetic evidence for the classification of typical and atypical isolates into separate taxa (Belland and Trust, 1989). These workers found that typical isolates possessed a very homologous plasmid content comprised of a single large (70-145 kb) plasmid and three low molecular weight plasmids. Livesley et ai, (1997) reported that 5 plasmids were most common among the 18 isolates examined; Giles et al. (1995) found 4 or 6 plasmids with 4 smaller plasmids of 4.3-8.1 kb being often observed in isolates from the Atlantic coast of Canada, but 6 plasmids of 4.2-8.9 kb among cultures from the Pacific coast of Canada. A total of 23 plasmids and 40 different plasmid profiles were recognised among 124 isolates from Denmark, Norway, Scotland and North America (Nielsen et al, 1993). An earher theme was repeated insofar as all isolates had one large plasmid of 60-150 kb, and two low molecular weight plasmids of 5.2 and 5.4 kb. In addition, two plasmids of 5.6 and 6.4 kb were frequently present (Nielsen et al, 1993). A larger investigation of 383 isolates over a 6-year period concluded that 1-4 plasmids of 52-105 mDa were inevitably present, casting doubt on the relevance of plasmid typing for epizootiology (S0rum et al, 1993b). Again, oxytetracycline- and streptomycin-resistant isolates from the Atlantic and Pacific coasts contained 4 or 6 plasmids, with 4 smaller plasmids of 4.3 to 8.1 kb being often observed. Some sHght variation in plasmid content was noted between sources of the isolates (Giles et al., 1995). Atypical isolates possessed two to four different plasmid types (Belland and Trust, 1989). Moreover, there was a correlation between plasmid composition and source of the atypical isolates. This observation may prove useful in epizootiological studies, where plasmid content of atypical isolates could serve as useful markers (Belland and Trust, 1989). In a subsequent investigation of 113 cultures of atypical isolates from a wide range of geographical locations, 7 groupings were defined; 18 cultures did not have any common plasmid profile. Of interest, the two type strains NCIMB 1110 and ATCC 27013 were recovered in different groups. For some groups, i.e. I, III, V and VII (these isolates were catalase-negative), there was an association with the origin of the cultures, i.e. the location of the farm. Also, some differences in
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94 Bacterial Fish Pathogens phenotype were apparent between members of some groups. Again, the value for epizootiological investigations was stressed (S0rum et ai, 2000).
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  • Bacteria, representative, gram-negative bacteria

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