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[Construction and characterization of recombinant Salmonella enterica serovar choleraesuis vaccine strain expressing heterologous antigen of Pasteurella multocida toxin].

OBJECTIVE
This study was aimed to construct and characterize Salmonella vaccine strain C500 expressing the recombinant Pasteurella multocida toxin (PMT) antigen by the Asd+ balanced-lethal host-vector system.


METHODS AND RESULTS
The DNA fragment encoding C terminal of PMT was cloned downstream from the beta-lactamase signal sequence in the multicopy Asd+ pYA3493 vector to create pYA-PmtC. Fermentation patterns, serotype, and mean generation time of the vaccine strain C500 harboring pYA-PmtC (named with C501 (pYA-PmtC)) were identical to those of the parent strain C500. The recombinant pYA-PmtC plasmid was very stable in C501 (pYA-F1P2), which expressed secretorily a large amount of the recombinant PMT antigen (named with rPmtC). The virulence of C501 (pYA-PmtC) with LD50 of 8.5 x 10(6) CFU was a little lower than C500 with LD50 of 4.4 x 10(6) CFU based on the method of Reed and Muench. All piglets inoculated with C501 (pYA-PmtC) or C500 survived, and had no signs of disease during the entire experimental period. No significant differences were found between these two groups.


CONCLUSION
The recombinant vaccine strain C501 (pYA-PmtC) had a series of biological characteristics silimar to the parent vaccine strain C500. It is likely that C501 (pYA-PmtC) could be adapted to develop multivalent recombinant Salmonella vaccine against both infections with S. enterica serovar Choleraesuis and toxigenic P. multocida.