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 x 10(3) cfu/g of fish (5.2 x 10(5) cfu/fish) and 1.9 x 10(3) cfu/g of fish (8.9 x 10(2) 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 (30 microg) and ceftriaxone sodium (30 microg). Present study describes P. damselae subsp. piscicida from diseased fish for the first time in China.