| In recent years the explosive epidemic of Streptococcus agalactiae has bring a severe damage to aquaculture and causing large economic losses in cultured Tilapia, which is one of the sensitive hosts of GBS. Furthermore, the main serotype of GBS prevalent in China is Ia. The chemicals are the first choice normally when the GBS outbreaks, and the antibiotics are currently used in the treatment of streptococcus infection in tilapia. Because of the heritable variation of GBS, it turn to be resistant to kinds of medicine, so that there are little antibiotics effective to GBS. In order to solve the problem about the treatment of streptococcal infection fundamentally, further research and looking for more effective and safe new drugs are essential. During the process for searching the alternatives to antibiotics, the immunoglobulin of egg yolk (IgY) come to the eyes of researchers because of its advantages for do not activate complement and do not bind to Fc receptors of human rheumatoid factor, what's more it can react with more heterologous epitopes on the antigen. In addition, the low cost in preparation, high output, simple and efficient in purification, good stability in acid and alkali also bring it a great potential in the future.In this study, the hens were immunized by Ia strain GBS/HN0303, then the eggs were collected to prepare specific IgY through the method chloroform and saturated ammonium sulfate salting. Then the physicochemical property and speciality for IgY were detected by slide agglutination test, Western bloting, bacterial staining, ELIS A and tube agglutination test. Then evalute the antibacterial effect by in vitro antibacterial and antiviral test.1. Preparation effects and physicochemical properties of IgYThe hens were immunized four times by inactivated vaccine which made from the bacteria in concentration of 109CFU/mL, as a result the content of IgY get to peak which is 1:100000 at 48d after three times of booster immunization and maintain for one month at least. The binding activity of sp-IgY was demonstrated by slide agglutination test, Western bloting and bacterial staining. In addition the IgY can be stable at low temperature environment and pH 3-7.2. Inhibitory effect of the specific IgY in vitroThe inhibitory of the IgY on the growth of GBS was tested in liquid medium and soild medium. After 12h incubation with the specific IgY (500?g/mL) at 28?, the growth of GBS significantly decreased compared with the control ones in liquid medium. While in soild medium the inhibitory effect of IgY was positively correlated with the component content. It also proves that sp-IgY can neutralize GBS/HN0303.3. Disease resistance in vivoThe efficacy of prevention and treatment were tested by intraperitoneal injection and oral administration experiment. On the one hand the specific IgY can enhance immunity and put off the progression which decrease the mortality compared with the control ones, on the other hand the protective rate is positively correlated with the content of sp-IgY in fodder, which reach to peak at 46.7%. It also prove that the dose-effect relationship play an important role during the disease process.In conclusion, the specific IgY preparation in this study can provide a novel approach to the prevention and treatment of GBS infection, which will have a industrial prospect. |
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