[Salmonella choleraesuis C500 delivering DNA immunization against classical swine fever virus]

Classical Swine Fever Virus (CSFV) E2 protein eukaryotic expression plasmid pVAXE2 was constructed. The plasmid pVAXE2 was transformed into Salmonella choleraesuis C500 (S. C500) attenuated vaccine strain by electroporation to generate Salmonella choleraesuis engineering strain S. C500/pVAXE2. The characterization of S. C500/pVAXE2 in morphology, growth, biochemistry and serology indicated that it retained the same properties as its original strain S. C500 with exception of kanamycin resistance originated from the plasmid pVAXE2. The plasmid stable in the bacteria after 15 passages. Kunming mice and rabbits were vaccinated three times at two weeks interval with S. C500/pVAXE2 in oral and intramuscular routes at the dosage of 1 x 10(8) CFU for mice and 2 x 10(9) CFU for rabbits each time. The specific antibody response against CSFV and Salmonella choleraesuis was detected by ELISA. Two weeks after the third boost the immunized rabbits were challenged with 20 ID50 of hog cholera lapinized virus (HCLV), followed by a virulent strain of Salmonella choleraesuis two week later than HCLV challenge. The results showed that all immunized mice and rabbits produced significant antibodies against CSFV and Salmonella choleraesuis, and the immunized rabbits demonstrated the effective protection against the challenge of HCLV and virulent Salmonella choleraesuis. These results indicated the potential of developing multiplex swine DNA vaccine by using this bacteria as the vector.