damselae At water temperatures of 160 165C the fish developed large ulcers in 3

Damselae at water temperatures of 160 165c the fish

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damselae. At water temperatures of 16.0-16.5°C, the fish developed large ulcers in 3 days, with death following 24 h later. Similar data were recorded after experimental challenge of unscarified animals. However, in the initial study fish from other famihes appeared to be unaffected by Ph. damselae, pointing to host specificity of the pathogen. Thus, representatives of Atherinidae, CHnidae, Cottidae, Embiotocidae, Girellidae and Gobiidae resisted experimental challenge. This is interesting because representatives of these families co-habited the reefs with blacksmith (Love et al., 1981). However, Grimes et al. (1984a,b) and Labella et al. (2006) successfully infected dogfish and red-banded sea bream (LD50 = 3.9 x 10^ CFU/g offish) by i.p. injection with Ph. damselae. Death ensued in the dogfish within 18 h at an unspecified water temperature. Grimes et al. (1984a,b) reported that the organism was highly cytotoxic. A neurotoxic acetylchoHnesterase has been described (Perez et al., 1998). ECP have been imphcated with disease (cytotoxic) processes, with the LD50 dose ranging from 0.02-0.43 |ig of protein/g of fish with death occurring between 4 and 72 h after administration (Fouz et al., 1993). The ECP were considered to have low proteolytic activity, without evidence of any caseinase, elastinase or gelatinase. In contrast, pronounced phospholipase and haemolytic activity was recorded for turbot (and human and sheep) erythrocytes. It was possible that LPS contributed to heat stability of the toxic fractions (Fouz et al., 1993). A siderophore-mediated iron-sequestering system has now been described, and almost certainly contributes to the pathogenicity of the organism (Fouz et al., 1994, 1997). Photobacterium damselae subsp. piscicida Experimental infection may be achieved by i.m. injection, oral uptake or immersion, with maximum mortalities at 18 and 20, but fewer at 15°C (Magarinos et al., 2001). Medium composition, and in particular the presence of yeast extract and/or (fish) peptone, enhanced the toxicity of ECPs and the virulence of cells administered via immersion or i.p. injection (Bakopoulos et al., 2002). The fate of the pathogen has been examined by FAT (Kawahara et al., 1989). Thus, following i.m. injection, the pathogen became located initially in the kidney and spleen, before spreading to the gills, heart, intestine and pyloric caeca. Following oral uptake, the pathogen appeared in the stomach, before spreading to the internal organs. After immersion. Ph. damselae subsp. piscicida located in the gills, and then spread widely to the heart, kidney, liver, pyloric caeca and spleen (Kawahara et al., 1989). Within the tissues of
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Pathogenicity 325 infected fish, Ph. damselae subsp. piscicida was seen to accumulate and multiply in the macrophages (Nelson et ai, 1989; Elkamel et ai, 2003), perhaps after an initial cell adherence stage (Magarinos et al, 1996a, b), which appears to involve capsular polysaccharide (this is dependent on the presence of iron and younger, i.e. logarith- mic, rather than lag phase cultures) (Magarinos et al, 1996b; do Vale et al, 2001), which has a minor role in the binding of haemin (do Vale et ai, 2002). The surface-
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