Characteristics of Vibrio vulnificus isolated from diseased tilapia [Sarotherodon niloticus; Japan]

Three halophilic Vibrio strains were isolated from diseased tilapia (Sarotherodon niloticus) cultured in the ponds located near by sea in Kagoshima Prefecture of Japan. The present isolates were identified as Vibrio vulnificus based on their morphological and biochemical characteristics; they were positive for fermentation of galactose, cellobiose, lactose and salicin, decarboxylation of lysine and ornithine, and growth at 42°C, while negative for arginine dihydrolase, V. P. reaction and sucrose fermentation. Two strains producing extracellular protease of high activity were resistant to human and tilapia sera, and pathogenic for tilapia and carp (Cyprinus carpio). One strain exhibiting low protease activity was also serum resistant and virulent for fish. A spontaneous mutant, which lost motility and decreased protease production, was non-pathogenic for fish.