When administered im at doses of just over 10 cellsfish Str dysgalactiae led to

When administered im at doses of just over 10

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When administered i.m. at doses of just over 10^ cells/fish, Str. dysgalactiae led to cHnical disease resembling that of naturally infected fish (Nomoto et al, 2004). An isolate of Str. milleri (G3K) injected at 5 x 10^ cells/fish caused 20% mor- talities in Atlantic salmon. Interestingly, all the fish darkened, albeit with negligible signs of internal or external abnormalities. With rainbow trout, there was evidence of kidney liquefaction (Austin and Robertson, 1993). Str. parauberis were examined for the presence of putative surface-associated virulence factors relevant to turbot for which the data indicated haemagglutination activity (against turbot erythrocytes), variable hydrophobicity due possibly to the presence of capsular material, and the ability to adhere to and invade cultured cells, e.g. CHSE-214 (Chinook salmon embryo) and SBL (striped bass larvae) cell Hnes (Romalde et ai, 2000). AEROBIC GRAM-POSITIVE RODS AND COCCI Renibacterium salmoninarum Pathogenicity experiments have met with varying degrees of success. Mackie et al. (1933, 1935) succeeded in transmitting "Dee disease" to brown trout by subcutaneous and i.m. injections of emulsified spleen from Atlantic salmon. In these experiments, death followed in 5 weeks, although typical lesions, as found in field situations, did not occur. A similar observation was made by Belding and Merrill (1935) who injected, intramuscularly, brook trout with purulent material collected from kidney abscesses in the same species. Death followed in 18 to 25 days, but characteristic BKD lesions did not occur. This was, however, achieved by Earp (1950) following the
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286 Bacterial Fish Pathogens injection of chinook salmon with a pure culture of the BKD organism. Koch's postulates were finally satisfied by Ordal and Earp (1956) following the estabhshment of BKD in chinook salmon after i.p. injection of an organism obtained from sockeye salmon. MortaHties started after 12 days, and continued until day 23, when all the fish were dead. At this point, the organism was re-isolated. Sakai et al. (1989c) found mortalities began 17 days after rainbow trout were injected with 4x10^ cells. In comparison, carp {Cyprinus carpio) were markedly resistant. Failure greeted the attempt by Snieszko and Griffin (1955) to transmit BKD to brook trout by co- habiting with diseased fish for 21 days, followed by feeding with infected viscera. However, using feeding, success was achieved by Wood and WalHs (1955) with 100% infection of 993 chinook salmon fingerlings. Later, Wolf and Dunbar (1959) achieved success by immersing experimentally wounded brook trout into a suspension of the pathogen. Murray et al. (1992) succeeded in inducing BKD in chinook salmon by immersion (10^-10^ cells/ml for 15-30min) and co-habitation with other experimen- tally infected fish. However, the time to death was much longer than in most experimental models. By co-habitation and immersion, the average periods leading to mortahties were 145 and 203 days, respectively. Transmission from wild to cultured fish has been reported (Mitchum and Sherman, 1981) and vice versa (Frantsi et al, 1975). Prior infection with Ren. salmoninarum
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