Later the genus Aeromonas was moved again to the family Vibrionaceae and more

Later the genus aeromonas was moved again to the

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Later, the genus Aeromonas was moved again, to the family Vibrionaceae and more recently to its own family, i.e. the Aeromonadaceae (Colwell et ai, 1986). The initial re-classification was based primarily on the work of Griffin et al. (1953a). This team undertook the first detailed characterisation of the organism, providing the informa- tion necessary to formulate the description, which resulted in its re-classification. However, the division of Aer. salmonicida strains into subspecies remains an ongoing bone of taxonomic contention. The description of Aer. salmonicida subsp. pectino- lytica opens a new chapter in the understanding of the organism insofar as this is the first subspecies which is not associated directly with fish diseases (Pavan et al., 2000). Instead, the isolates were recovered from a polluted river in Argentina (Pavan et al, 2000). To date, there is not any evidence to link this subspecies with fish pathogenicity. Two aspects concerned with the status of Aer. salmonicida in the bacterial taxonomic hierarchy require discussion. One centres on the intraspecific relationships of Aer. salmonicida strains; the other is involved with questions that have been raised regarding the retention of the species in the genus Aeromonas. Aer. salmonicida has been known by its present name since the 1950s when, on the basis of work by Griffin et al. (1953a), Snieszko (1957) in his contribution on the genus Aeromonas in the seventh edition of Bergey's Manual of Determinative Bacter- iology assigned the pathogen to this genus, where it has remained. It is curious, in view of its seriousness as a pathogen, that it was over 50 years from the initial discovery of the organism to the characterisation and description of Aer. salmonicida. Griffin et al. (1953a) provided the first detailed description of the organism, and were of the opinion that attempts to recognise and identify isolates were being hampered by a lack of a complete description. This resulted in confusion due to disagreement
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86 Bacterial Fish Pathogens concerning the physiological and biochemical characterisation of the organism. >From the results of a study of ten isolates, it was concluded that Bacterium salmonicida was extremely consistent in its general cultural and biochemical traits, and that problems in the past had arisen primarily from the use of media which varied in composition among laboratories. Although Griffin et al. (1953a) ended their report by recommending the re-classification of Bacterium salmonicida to the newly created genus Aeromonas, as Aer. salmonicida, no definite reasons were given for this move. However, with time, additional data have accumulated, and the homogeneity and authenticity of the taxon has generally been supported. Subsequent investigators have re-examined the homogeneity of the taxon, using conventional and numerical phenetic methods (Eddy, 1960; Ewing et al., 1961; Schubert, 1961; Smith, 1963; Eddy and Carpenter, 1964; Popoff', 1969). Thus, the traditional description of Aer. salmonicida is of non-motile, fermentative. Gram-
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