Isolation Of Bdellovibrio Bacteria From The Gut Of Eel And The Study Of Its Prevention Of Bacterial Diseases In Aquaculture

The contents of the gut of eel was collected by aseptic method, and one kind of bacterium which could prey on other bacteria was isolated by using Aeromonas hydrophila, a pathogenic strains of multiple aquatic animal disease, as host. Using standard strain 109J as reference, it was judged as Bdellovibrio by its morphological characteristics and bionomics and was named as Bdm4. Bdm4 was an gram-negative bacterium with the form of long and short rod. Its size was about 0.3 ~ 0.4μm×1.2 ~ 1.5μm witlh a long flagellum at one end. After research on the bionomics of Bdm4, it showed that Bdm4 can reproduce at the temperature ranged from 10℃to 35℃, and the optimum growth temperature was 25℃.When the cultivating temperature was lower than 20℃or higher than 30℃, the its'growth decreased very significantly. The optimum growth pH was during 7～8, and it almost could not reproduce when pH was below 4. Bdm4 cultivated with medium could reproduce when the concentration of NaCl was below 5%, and the optimum growth salinity was about 1%. When the concentration of NaCl was above 2%,the number of plaques decreased as the concentration of salt increased. Bdm4 can prey on all the pathogenic strains within sea and fresh water , which was selected for the experiment, and can lyse V.alginolyticus sharply and decrease the proportion of survival V.alginolyticus to 2%. Bdm4 can not prey on the selected probiotics, while can prey on the heated nonhost bacteria , Bacillus subtilis.The safe test was carried out through drenching crucian carps with 106pfu/mL Bdellovibrio Bdm4. All the carps of test group and control group were healthy. This result showed Bdm4 was safe to crucian carps. After soaking crucian carps with 104pfu/mL Bdm4 or feeding crucian carps with bait mixed with 106pfu/mL Bdm4, there were considerable Bdellovibrio on the body surface, gill and intestinal tract of fish, and the number of Bdellovibrio was significantly larger than that of the control group. Infected crucian carps, which were soaked with 104pfu/mL Bdm4 or fed with bait mixed with 106pfu/mL Bdm4, with Edward. And detected the number of Edward from fish boby, it showed that the number of test group was significantly lower than that of the control group. It demonstrated that Bdellovibrio could protect fish. Feeding Sparus latus with Bdm4 and detecting the major microbial population of intestinal tract, the numbers of both E. coli and Vibrion of the test group were sharply decreased, while the number of lactobacillus was relatively higher than that of the control group but there were not too many lactobacilli. Throwing Bdm4 into the cultivation water, the total count and the number of Vibrion decreased more quickly than the control group did.Feeding carp and Sparus latus with mixed Bdm4 and infecting them with Aeromonas hydrophila and Vibrio alginolyticus, the survival rate of the control group was 65% and 55% respectively while the rate of the test group was only 35%. Through soak treatment to prevent the Vibriosis parahaemolyticus and digestive caecus intumescence of Litopenaeus setiferus Linnaeus , and the survival rate of the test group was 45% and 67.5% respectively while the rate of the control group was 17.5% and 40% separately. Bdellovibrio Bdm4 is effectively to prevent bacteriosis in aquatic animals. Both carp and Sparus latus were infected with Aeromonas hydrophila and Vibrio parahaemolyticus, and were treated with Bdm4 after morbility, and the result was that there was not conspicuous differences between the survival rate of the test group and the control group. Bdellovibrio Bdm4 can not used to cure the disease in aquatic animals.The results of this study indicated that Bdellovibrio Bdm4 can prey on most pathogenic strains of aquatic animal disease, and can effectively prevent aquatic animals from being infected by pathogenic bacteria. It might have widely-used prospective as probiotics.