Identification of Aeromonas salmonicida associated with skin ulceration of cultured sea cucumber Apostichopus japonicus and characterization of the extracellular products

Bacterial strain H1,which was isolated from the diseased cultured sea cucumber Apostichopus japonicus with skin ulceration,was proved to be a pathogen by soaking with bacteria suspension,soaking with bacteria suspension after the sea cucumbers were wounded,coelom injection and muscle injection with bacteria suspension.The LD50 doses of soaking with suspension of bacteria after wound and muscle injection were 2.26×107 CFU/ind and 1.80×107 CFU/ind By methods of morphological observation,physiological and biochemical characteristic analysis and mini API systematic identification,strain H1 was identified as Aeromonas salmonicida masoucida.The lethality of the extracellulose products(ECP) of strain H1 was detected by injecting ECP to A.japonicus,the LD50 dose was 5.24 μg(protein)/g body weight.The ECP exhibited casinase,gelatinase,chitinase,amylase and haemolytic activities.The protease specific activity of ECP to azocasin was 674.5 U/mg protein when at the optimum temperature 50 ℃.The ECP was instable to heat and was inactivated at 70 ℃ and the toxicity to the sea cucumber disappeared after incubation at 100 ℃ for 30 min.The enzymatic activity could be inhibited by 10 mmol/L EDTA and 5 mmol/L PMSF,and Ca2+ and Mg2+ could increase enzymatic activity by 9% and 4%,respectively.