无毒力沙门菌作为口服菌苗载体表达外源基因的研究引起人们的兴趣.活菌苗株要求不带有抗生素抗性标记.为此,作者将as-dAI基因缺失引入沙门菌△cya△crp减毒菌苗株,以asd基因产物二氨基庚二酸(DAP)作为选择标记.同时构建具有asd基因的互补性质粒,成为无抗生素抗性标记.且能稳定表达外源基因的平衡致死系统. Toxicity of Salmonella as an Oral Vaccine Vector for Expression of Exogenous Genes is of Interest Because Live Vaccine Vaccines Are Not Required to Have Antibiotic Resistance Marker To this end, the authors introduced the deletion of as-dAI gene into Salmonella △ cya △ crp attenuated vaccine strain, using the asd gene product diaminopimelic acid (DAP) as a selection marker and constructing a complementary plasmid with asd gene as a marker without antibiotic resistance, and can stably express the balance of lethal genes system.