Abstract:An outbreak of serious mortality among the cultured black sea bream Sparus macrocephalus, characterized by a swollen intestine containing yellow fluid, occurred in early spring of 2008 in Xiangshan Bay, Zhejiang Province. Four strains of bacteria, BB01, BB02, BB03 and BB04 were isolated from the intestinal yellow fluid of the moribund black sea bream with Zobell2216E agar and/or thiosulfate citrate bile salt sucrose agar. The former three were identified as causative agents via artificial challenge. The 96h LD50 value of BB01 was 461×104 CFU/g bream body weight. The former three strains were characterized as Pseudomonas putida through morphological, physical and biochemical profiles tests and 16S rRNA sequencing. The three strains were Gram negative, short rod shaped, oxidase and glucose oxidation positive, gas negative, maltose and citrates utilization positive, arginine dihydrolase positive, nitrate reduction positive, DNA enzyme and acetamidase negative. The 16S rRNA sequence of BB01 shared the identity of over 99% with those of P.putida strains. Drug sensitivity tests showed that the strain BB01 was susceptible to most of the tested antibiotics while resistant to ofloxacin.
