Isolation of Photobacterium damselae subsp. piscicida from diseased tongue sole (Cynoglossus semilaevis Gunther) in China

Abstract:

During the summer of 2006，an epizootic occurred among cultured tongue sole (Cynoglossus semilaevis Gunther) in a fish farm in Qingdao，China. The diseased tongue sole exhibited haemorrhaging of the basal fin，yellowed kidney and ulceration of the body surface. A Gram-negative，rod shaped bacterium (designated strain WY06) was isolated from the gall bladder of diseased fish. Pathogenicity assays revealed that WY06 was virulent to tongue sole and zebrafish (Danio rerio) by intraperitoneal injection challenge，with the LD₅₀ being calculated as 5.5×10³ cfu/g of fish (5.2×10⁵ cfu/fish) and 1.9×10³ cfu/g of fish (8.9×10² cfu/fish) respectively. The 16S rRNA gene sequence of strain WY06 demonstrated high similarity (99%) with Photobacterium damselae subsp. piscicida. Phylogenetic analysis showed a clear association of strain WY06 with P. damselae subsp. piscicida. Additional evidence of the identification included in morphological，physiological and biochemical data. The pathogen was sensitive to cifuroxime (３０μg) and ceftriaxone sodium (３０μg). Present study describes P. damselae subsp. piscicida from diseased fish for the first time in China.