Similar non motile variants were also recovered from previously vaccinated

Similar non motile variants were also recovered from

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2005a). Similar non-motile variants were also recovered from previously vaccinated rainbow trout in Spain (Fouz et al, 2006). Flavobacteriaceae representatives Numerous reports have centred around the role of Gram-negative chromogens as agents of fish disease. Genera, which have been mentioned frequently, include Cyto- phaga, Flavobacterium, Flexibacter, Myxobacterium, Myxococcus and Sporocyto- phaga. The common factor is that these genera comprise difficult-to-identify species, a taxonomic re-evaluation of which has at long last occurred. Moreover, from the early literature it is often uncertain into which of these genera unknown isolates should have been placed. In particular, the distinction between Cytophaga and Flexibacter was confusing (Christensen, 1977; Allen et al., 1983b). The authen- ticity of Flavobacterium has been questioned repeatedly, insofar as it became a recipient of problematical pigmented bacteria. Fortunately, more recent work has improved the taxonomy of Flavobacterium (Holmes et al, 1984; Bernardet et al.
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Characteristics of the pathogens: Gram-negative bacteria 113 1996). Myxobacterium, considered to be a causal agent of gill disease (Ghittino, 1967; Wood, 1968; Bullock and McLaughlin, 1970; Ashburner, 1978), is not included in the "Approved Lists of Bacterial Names" (Skerman et al, 1980) or their supplements. Therefore, this genus lacks taxonomic meaning. It is possible that the organisms identified as Myxobacterium (and referred to as myxobacters) belong in either Cyto- phaga, Flavobacterium or Flexibacter. Historically, interest in chromogenic. Gram-negative bacteria started with a pubHcation by Davis (1922), who reported serious mortalities (columnaris) among warm-water fish, namely small mouth bass and common perch, from the Mississippi River. These fish were held at the U.S. Biological Station at Fairport, Iowa, when the disease occurred. Davis recognised two important features of the disease, namely that occurrence was primarily in injured (damaged/stressed) fish, and that the water temperature was high, i.e. >21.1°C. Unfortunately, Davis did not succeed in isolating the pathogen. In fact, this was not achieved for two decades, until Ordal and Rucker (1944) succeeded in 1943 during an outbreak in hatchery-reared sockeye salmon. Fish-pathogenic flexibacters have been recognised (see Masumura and Waka- bayashi, 1977; Hikida et aL, 1979; Pyle and Shotts, 1980, 1981; Wakabayashi et aL, 1984). For example, during 1976 and 1977, a bacterial disease developed in juvenile (usually <60 mm in length) red sea bream and black sea bream maintained at marine sites in Hiroshima Prefecture, Japan. The outbreak occurred 1-2 weeks after the fish were transported from the hatchery to sea cages. An organism was isolated by Masumura and Wakabayashi (1977), and later considered to be a new species of Flexibacter, for which the name of Fie. marinus was coined (Hikida et ai, 1979). This organism was subsequently re-named as Fie. maritimus (Wakabayashi et al., 1986) and thence as Tenacibaculum maritimum (Suzuki et al., 2001). However, it has been suggested that this taxon is synonymous with Cyt. marina (Holmes, 1992).
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