伤寒沙门氏菌能通过粘附、侵袭、定居在肠道相关淋巴组织，并经肠系膜淋巴结到达肝脏、脾脏，进一步有效地刺激机体产生粘膜、细胞和体液免疫应答。近几年，常以减毒伤寒沙门氏菌为载体构建双价、多价活菌苗，成为新型菌苗研制的重要途径之一。为避免在基因工程活菌苗的研制中使用抗药基因作为选择压，将载体一宿主平衡致死系统应用于减毒伤塞沙门氏活菌疫苗中，使在没有抗菌素存在的情况下，外源保护性抗原能在减毒伤寒沙门氏菌中稳定表达，具有广泛的应用前景 Salmonella typhi can adhere to and attack, colonize the gut-associated lymphoid tissue, and reach the liver and spleen through the mesenteric lymph nodes, further stimulating the body to produce mucosal, cellular and humoral immune responses. In recent years, often with attenuated Salmonella typhimurium as vector to build bivalent, multivalent live vaccine has become one of the important ways for the development of new bacterins. In order to avoid the use of drug-resistant genes as selection pressure in the development of genetically engineered live vaccine, the carrier-host balance lethal system was applied to attenuated Salmonella enteric vaccine, so that in the absence of antibiotics, exogenous Protective antigen can be stably expressed in attenuated Salmonella typhimurium and has a wide range of applications