Cytophagas became implicated as fish pathogens with the work on coldwater low

Cytophagas became implicated as fish pathogens with

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Cytophagas became implicated as fish pathogens with the work on coldwater (low-temperature) disease. The causal agent was initially isolated and described by Borg (1948), and subsequently named as Cyt. psychrophila (Borg, 1960), and then to Fla. psychrophilum (Bernardet et al, 1996). Coldwater disease affects predominantly juvenile salmonid fish, notably coho salmon in the northwest U.S.A., and is most prevalent in winter and spring when the water temperature is <10°C. Cranial and vertebral lesions may occur (Kent et al., 1989). More recently, the organism has been associated with systemic disease in eels and cyprinids in Europe (Lehmann et al., 1991) and with an anaemic condition of juvenile rainbow trout in Chile (Bustos et al, 1995) and Europe (e.g. Lorenzen et al, 1991), referred to as rainbow trout fry syndrome (RTFS) (Baudin-Lauren9in et al, 1989; Lorenzen et al, 1991). A causal mention was given initially to the role of Cyt. johnsonae and Cyt. rosea as fish pathogens (Christensen, 1977). Cyt. johnsonae has emerged as a problem in Australia. However, only scant information is available about Cyt. rosea; therefore, this organism will not be considered further. An organism was recovered initially from the gills of diseased, hatchery-reared salmon, trout and suckers in Michigan (Strohl and Tait, 1978). Thirteen isolates were recovered, and although similarities were noted to organisms previously described by Borg (1960), Pacha and Porter (1968) and Anderson and Conroy (1969), it was decided to elevate them into a new species, as Cyt. aquatilis (Strohl and Tait, 1978), and thence to Fla. hydatis (Bernardet et al, 1996). It must be emphasised that Strohl and Tait (1978) did not prove that the organisms were capable of causing disease. Nevertheless, we have recovered similar organisms from outbreaks of gill disease in farmed rainbow trout from England.
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Characteristics of the pathogens: Gram-negative bacteria 115 Cytophaga sp. has been associated with skin and muscle lesions on Atlantic salmon in the U.S.A. (Kent et ai, 1988), and a previously undescribed Cytophaga- like bacterium (CLB) has been associated with a gill and systemic disease in turbot (Mudarris and Austin, 1989). This organism was described as a new species, as Fla. scophthalmum (Mudarris et aL, 1994), which was re-classified to Chrys. scophthalmum (Vandamme et aL, 1994). Little is known about the role of Sporocytophaga as a fish pathogen. Mixed infections attributed to Sporocytophaga and V. anguillarum occurred as surface lesions, termed saltwater columnaris, on salmon and trout held in marine conditions (Wood, 1968). However, apart from discussing the presence of microcysts which began to form at 2-7 days, there is little information about this suspected pathogen (Pacha and Ordal, 1970). Chryseobacterium balustinum (= Flavobacterium balustinum) The original description was extremely brief, referring to the growth of colonies at very low temperatures, i.e. 1-3°C, rod-shaped micromorphology, motility and the ability to degrade gelatin (Harrison and Sadler, 1929). The revised description of Flavobacterium excludes motile organisms (Holmes et aL, 1984); therefore, the vaHd- ity of Fla. balustinum was doubtful. The organisms were re-classified to
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  • Spring '20
  • Bacteria, representative, gram-negative bacteria

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