Studies On Pathogenic Bacteria Of Abalone Postlarvae (Haliotis Diversicolor Supertexta) And Potential Biotic-Control

With the development of abalone aquaculture, the various diseases have been come into been frequently and tempestuously. The diseases of grown abalone haven't been resolved, whereas mass death of abalone postlarva occurred. Many antibiotics and bacteriophages have been used to control the diseases. However, all the measures at present are temporary and have engendered serious hazards of increase of bacterial drug resistance of environment. Simultaneously, the antibiotics and bacteriophages abuse leads to immune system damage of abalone postlarva, thus it will induce the massive death of abalone postlarva when aquaculture environment change abruptly. As the above reason, 124 bacterial strains were isolated from the water, whitened postlarvae and their bio-films of an abalone farm in Guangdong Province. Physiological-biochemical characteristic, bacterial classification, susceptivity of antibiotics, extra-cellular products as well as haemolytic tests was performed on them. Lysophospholipase (Tlh)-targeted PCR was also carried out in order to reveal if the haemolysis caused by bacterial strains were related to T1h genes. On the base of above research, challenge test carried out to reveal pathogen caused massive death of abalone postlarva. In order to find out an environmental protection and effective microbial ecological agent to prevent and cure the diseases of abalone postlarva, four bdellovibrioes were isolated from the sea bottom mud. lysis spectrum and their physiological-biochemical characteristic to pathogens were investigated.Results of extra-cellular products of isolates showed that the proportion of bacterial strains which produced extra-cellular caseinase, glutinase, lipase and hemolysin were 58%, 53%, 44% and 26% respectively. On the base of above experiments, 35 strains were selected as the potential pathogen.By Gram's staining, 33 strains were identified as gram-negative bacterium except No. 7 and No. 14.that was gram-positive bacterium, which proportion was 94.3%. The exponential growth phases of 35 strains were between four hours and twelve hours and their concentrations were above 10~9 CFU/mL after ten hours. In order to identify these strains, API 20 E strips were employed and results indicated that bacteria were mainly comprised of Vibrio alginolyticus, Vibrio cholerae, Vibrio parahaemolyticus, Shewanella putrafaciens. Among them vibrios composed 50 of the strain population. The dominant species of vibrios were Vibrio alginolyticus, which...