| Avian pathogenic Escherichia coli(Avian Colibacillosis,AC)is avian infectious disease caused by avian pathogenic Escherichia coli(APEC),it is one of the most important bacterial diseases in the poultry industry.Because of the deficiencies of antibiotic resistance and drug residues in antibiotic treatment,effective vaccines are essential for the prevention and treatment of avian pathogenic E.coli..In this study,trivalent inactivated vaccine was made by adjuvanting with Montanide TSA 71 VG oil adjuvant with six strains,three strains of common serotypes O1(E516),02(E058),and 078(E522)of Avian pathogenic Escherichia co/i(APEC)and three of their mutant strains E516?lpxL?lpxM,E058?lpxL?lpxM,E522?lpxL?lpxM which lipopolysaccharide genes were modified in our laboratory,and were used to explore the safety,the optimal immunogenic antigen content,the duration of immunity,the cross-immune protection of vaccine candidates against epidemic strain challenge of mutant strain-based inactivated vaccine1 The safety comparison between parent strain-based inactivited vaccine and lpxL,lpxM mutant strainbased vaccineIn this study,the avian pathogenic E.coli E516(O1),E058(O2),E522(078),and their mutant strains E5l12lpxxL?lpxM,E058?lpxL?lpxM,E522?lpxL?lpxM constructed in our laboratory were respectively prepared a trivalent inactivated vaccine with an antigen content of 2.0 × 109 colony forming units(CFU/mL)and 2.0 ×1010 CFU/mL,and the safety was evaluated by injecting specific pathogen free(SPF)chickens at twice the normal dose.The results showed that the safety and the side-effect of the 2 × 109 CFU/mL vaccine were better than those of the 2× 1010 CFU/mL,Gegardless of parent strain-based or mutant strain-based vaccine.Meanwhile,the safety and side-effect of the 2.0 × 109 CFU/mL,the mutant strain-based inactivated vaccine were better than those of the parent strains-based vaccine.2.Optimum immunogenic antigen content of lpxL,lpxM mutant strain-based vaccineIn this study,the adjuvant trivalent inactivated vaccine of 01,02,078 serotype parental strain-based and lpxL,lpxM mutant strain-based inactivated vaccine with bacterinal content of 2.0 × 108.5 CFU/mL,2.0 × 109 CFU/mL,and 2.0 × 109.5 CFU/mL were prepared,respectively.After immunization,the optimum immunogenic antigen content of the parent strains-based vaccine and the mutant strain-based inactivated vaccine were determined based on the specific antibody level,the protection rate and the histopathological changes of the visceral tissues of birds after challenging with the parent strains The research data showed that in the 2.0 x 108'5 CFU/mL bacterin immune group,the protection rates against 01,02 and 078 strain challenge in the parent strain-based vaccine immune group were 50.0%,55.6%,and 55.6%respectively,in the mutant strain-based inactivated vaccine were 50.0%,55.6%and 66.7%,respectively.In the 2.0 ×109 CFU/mL bacterin immune group,protection rates against O1,02 and 078 strain challenge in the parent strain-based vaccine immune group were 80.0%,88.9%,88.9%,in the mutant strain-based inactivated vaccine group were 90.0%,88.9%,100%,respectively.In the 2.0 × 109.5 CFU/mL bacterin-based vaccine immune group,protection rates against 01,02 and 078 challenge in the parent strains were 70.0%,77.8%,77.8%respectively,in the mutant strain-based inactivated vaccine group were 80.0%,88.9%,100%,respectively.Therefore,it can be seen that the protection rates of the mutant strain-based inactivated vaccine were better than parental strains Trivalent Vaccine in the same immune antigen content.So,the optimal antigen content of the mutant strain-based inactivated vaccine is 2.0 × 109 CFU/mL.3.Immune duration of lpxL,lpxM mutant strain-based vaccineIn this study,the trivalent inactivated vaccine of lpx mutant strain-based was employed to vaccination.Then the parent strains used to challenged at 30th day,60th day,90th day,and 120th day after immunization,the specific antibody levels,protection rate of parental strains and pathological changes of vaccinated chickens were determined.The results showed that the protection rate of the vaccination-challenge birds against 01,02,and 078 strain challenge were 88.9%,87.5%,and 87.5%after 30 days post-vaccination.The protection rate of the vaccination-challenge birds against 01,02,and 078 strain challenge both were 66.7%after 60 days post-vaccination.the protection rate of the vaccination-challenge birds against 01,02,and 078 strain challenge were 50.0%,50.0%,and 66.7%after 90 days post-vaccination.After 120 days post-vaccination,it can be seen that both the chickens of immune group and control group were no dead.Therefor,After 30 days,60 days,90 days post-vaccination,the chickens were protected in different degree.However,there was no dead chicken founded in both the immunization group and the conrol group when challenged After 120 days post-vaccination because of the low sensitivity of adult chicken to avian pathogenic E.coli.So it is tentatively determined that the immunization duration of the vaccine is 3 months in this study.4.Study on cross immune protection of lpxL,lpxM mutant strain-based vaccineThe mutant strain-based inactivated vaccine were used to immunize in this study.The specific antibody level was detected after immunization,and the pathological changes of chicken visceral tissues were explored when the birds were challenged with the 01,02 and 078 parent strains and six currently isolated strains O1(Y12,T12),02(E172,E899)and 078(Y14,Y48).The results showed that the efficacy of the prototype vaccine immunized birds against O1 serotype E516,Y12 and T12 strain challenge were 88.9%,80%and 87.5%,respectively,and 87.5%,88.9%and 80.0%against 02 serotype E058,E172 and E899 strain challenge,respectively,and 88.9%,80.0%and 80%against 078 serotype E522,Y14,and Y48 strain challenge.The results in this study showed that mutant strain-based inactivated vaccine provided no less than 80%immunological protection,from both parent strain and current epidemic strain challenge... |
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