The fatty acids include lauric acid 3 hydroxy lauric acid myristic acid and

The fatty acids include lauric acid 3 hydroxy lauric

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and hexosamine. The fatty acids include lauric acid, 3-hydroxy lauric acid, myristic acid and palmitic acid (Salati et ah, 1989a, b; Hawke et al., 2003). The morphology and physiology of this pathogen led Snieszko et al. (1964a) to suspect a similarity to the genus Pasteurella. This view was reinforced by cross- precipitin reactions with Pasteurella (Yersinia) pestis. From this deduction, Janssen and Surgalla (1968) realised that, from an examination of 27 isolates, the organism was very homogeneous and different from existing species of Pasteurella. Therefore, the name of Pa. piscicida was coined. Independently, Kusuda gave it an alternative name, i.e. Pa. seriola, but quickly reahsed its synonymy with Pa. piscicida, which was accorded preference. However, Pa. piscicida was not included in the "Approved Lists of Bacterial Names" (Skerman et al., 1980) or their supplements. Consequently, the name of Pa. piscicida lacked taxonomic validity. A detailed taxonomic evaluation based on small-subunit rRNA sequencing and DNA:DNA hybridisation revealed that the organism was highly related to Ph. damsela (there was >80% relatedness of the DNA), and it was proposed that the organism be accommodated in a new subspecies, as Ph. damsela subsp. piscicida (Gauthier et al., 1995), the epithet of which was corrected to damselae (Triiper and De'Clari, 1997), as Ph. damselae subsp. piscicida. AFLP analysis revealed that the two subspecies are indeed distinct and separate entities (Thyssen et al., 2000). To complicate matters, there is controversy over interpretation of the Gram- staining reaction. The majority opinion is that the organism is Gram-negative. However, Simidu and Egusa (1972) considered that cells displayed Gram-variabiHty
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Characteristics of the pathogens: Gram-negative bacteria 131 when young, i.e. in 12-18 h cultures incubated at 20-25°C. In addition, they presented photographic evidence which showed that cells shortened with age. In fact, the suggestion was made that the pathogen is related to Arthrobacter. It is ironic that a similar phenomenon, concerning the interpretation of Gram-stained smears, was reported by KiHan (1976) and Broom and Sneath (1981) for Haemophilus piscium, the causal agent of ulcer disease. Piscirickettsiaceae representative Piscirickettsia salmonis Degenerate or obligately parasitic bacteria, i.e. chlamydias and rickettsias, have been long established as pathogens of invertebrates, and sporadically mentioned in con- nection with fish diseases (Wolf, 1981). Yet, firm evidence of their role in fish pathology has not been forthcoming until an upsurge of interest in Chile. Thus, since 1989 a disease coined "coho salmon syndrome", Huito disease (Schafer et al, 1990) or salmonid rickettsial septicaemia (Cvitanich et al, 1991) has been observed in coho salmon, chinook salmon, Atlantic salmon and rainbow trout, with a spread to Atlantic salmon in Norway (Olsen et ai, 1997) and white sea bass in California (Arkush et al, 2005). Losses fluctuated between 3-7% of stock per week, the cumulative mortahties reaching 90%. The organism was formally recognised as a new taxon, for which the name o^ Piscirickettsia salmonis was proposed (Fryer
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