RESUMO
In order to develop a safer vaccine strain exploit Salmonella Pullorum vaccine strain as a live vaccine vector.Methods:AΔcrpΔasd mutant of S.pullorum C79-13 strain was constructed and it was developed E.coli donor strain mutant was generated through the two-step method introduced by χ7213 ( pREΔasd) was conjugated with the recipient of C 79-13Δcrp.The C79-13ΔcrpΔasd the transduction of recombinant suicide plasmid .Results:PCR and sequencing results showed that ΔsipBSL1344 was suc-cessfully constructed.The further study indicated that foreign DAP must be supplied for the ΔcrpΔasd mutant to grow,in addition,the asd gene was transmitted stably .Compared with C79-13 strain,the O antigens was identical to C79-13 strain,but the growth velocity was reduced significantly ,significantly reduced virulence .Conclusion: The ΔcrpΔasd mutant can accept asd+plasmid to construct host-vector balance lethal system , and this system can be used to express foreign gene efficiently and to develop potential oral multivalent vaccines.