In vitro passages impact on virulence of Saprolegnia parasitica to Atlantic salmon, Salmo salar L. parr.
Bottom Line: The effect of serial in vitro subculturing on three pathogenic strains of Saprolegnia parasitica was investigated.Two of the strains declined in virulence after 15 successive in vitro subcultures, whereas one did not.It reveals that some strains degenerate more rapidly than others when subjected to successive in vitro subculturing on glucose-yeast extract.
Affiliation: Norwegian Veterinary Institute, Oslo, Norway.Show MeSH
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Mentions: By histopathology, a wide array of findings was evident in tissues infected with S. parasitica strains of different passages. One skin/muscle section from a fish infected with 5337AP showed necrosis of the epidermal layers extending into the dermis. There was very little inflammatory reaction present, and only a few neutrophils and lymphocytes were found in infected areas. Oedema and mild haemorrhage were also observed, with wipeout of the epidermis (Fig. 8a). The kidney interstitium of the same fish (5337AP) exhibited severe karyorrhexis and oedema (Fig. 8b). Mild pathological changes were detected in tissues collected from fish infected with 533715, characterized by moderate congestion of the liver (Fig. 8c) and mild degeneration on secondary lamellae of the gills (Fig. 8d). GMS staining did not show the Saprolegnia hyphae well, and the same was true for PAS, which showed very poorly defined hyphae (not shown).