| Silurus meridionalis Chen is a kind of valuable fish which can only be found in China. This kind of fish is featured by strong disease resistance and adults fish of this kind seldom suffer diseases. In October 2005, numerous adults of Silurus meridionalis Chen died in the fish farms around Chengdu and the mud fish farm of Sichuan province. The ulcer on skin of diseased Silurus meridionalis Chen is not obvious, and the serous membrane of stomach and intestine showed obviously edema and congestion. Furthermore, the intestine was almost erosive, and the liver widely scattered necrosis. All of these symptoms are different from the pre-reports. Later, three predomination strains of bacteria were isolated from the body of moribund fish. By artificial infection tests, strain TWN3 was confirmed to be the pathogen of the disease. From the morphology observation, this strain is gram-negtive and straight rod with no capsule and no forming spore, as well as motile by peritrichous flagella. Based on the characteristics of physiology and biochemistry, TWN3 was initially identified as Proteus. We designed a pair of primers and amplifed the the sequence of strain TWN3's 16S rDNA which is analyzed in the NCBI database. As a result, TWN3 has the highest similarity compared with P. vulgaris, with 99.52% identity. By constructing the molecular phylogenetic dendrogram with Minimum Evolution method in Mega3.1, it was revealed that TWN3 was in the same branch with P. vulgaris, and its G+C content of DNA is 39.1%. Based on all the results above, TWN3 is identified as P. vulgaris. With reference to Bergey's Manual of Systematic Bacteriology, Proteus vulgaris is divided into two groups, P. vulgaris BG2 and 3. According to the specific biochemical properties, such as acid production from sucrose, glycerol, maltose, D-xylose and salicin, and esculin hydrolysis, TWN3 is classified as a member of P. vulgaris BG3. Relevant tests of biological properties were also conducted, which showed that this strain has no haemolysis and is sensitive to four kinds of antibiotic such as gentamicin, kanamycin, furazolidone and norfloxacin, but insensitive to erythromycin, cefradine, penicillin and tetracycline, and so on. Moreover, crucian carps and mice are infected by the strain easily. The research on the growth property of strain TWN3 indicated that it has rapid growth rate and it grows better in the temperature range from 25℃to 39℃, pH from 4.0 to 11.0, salinity from 0.5% to 3.5%, and the optimum is 37℃, pH 6.0, and salinity 1.5%, respectively. Although the pathogenicity of P. vulgaris is extensive, there has been no report that P. vulgaris can infect cultivated Silurus meridionalis Chen so far. The researches on strain TWN3 enriches the pathogen of Silurus meridionalis Chen, which has the vital significance on prevention and therapy of the the catfish infection. In addition, the research on the taxonomy of Proteus vulgaris needs further thoroughly consummates, so the identification of strain TWN3 has positive effects on deeper research of the taxonomy of Proteus vulgaris.With reference to the result of the isolated strain BDTWll, a kind of Bdellovibrio bacteriovorus, schizolysis ability on strain TWN3, and the relvetant safety researches for crucian carps, we used the strain BDTWll to treat the crucian carps infected by strain TWN3 under the control outdoor conditionbased on establishing the infection test model of TWN3 on crucian carps, and the quantity ratio of the strain BDTWll and strain TWN3 is 1: 10. Then the effect of prevention and control of BDTWll to TWN3 was analyzed according to the statistical data of the death number of crucian carps. The result indicates that by the way of intraperitoneal injection of TWN3 and the BDTW11 intermixture to infect and prevent and cure the crucian carp, the crucian carp's survival percentage of the experimental group is remarkablely different from the control group, enhanced 10.8%; the result by the way of clyster is next, enhanced 6.6% compared to the control group; and the result by the way of soaking is enhanced 3.3% compared to the control group, which reveals that it is rarely different. So far, there have been very limited reports about the use of Bdellovibriois to prevent and control bacterial pathogen against fish under large-scale outdoor feeding condition and no report on Bdellovibriois as a control tool against P.valgaris. Moreover, the experiment on enlargement culture of Bdellovibriois was carried on, taking Escherichia coli and strain TWN3 as the host germ respectively, and it is revealed that the effect of enlargement culture about Bdellovibriois taking Escherichia coli as the host germ is not obvious, also the effect taking strain TWN3 as the host germ is opposite.The study above all has the certain academic value and the reference value to the taxonomy of Proteus vulgaris, preventing and controlling catfish diseases, the disease caused by Proteus vulgaris and the practical application of Bdellovibrio preparation. In addition, the research on the taxonomy of Proteus vulgaris, the growth property, route of infection, biological control of the TWN3, and the application and production of Bdellovibrio are discussed.
|
PDF Full Text Request