Provided is a nucleic acid system introduced into a bacterial strain to generate a genetically engineered bacterial strain that grows in solid tumors but does not grow in non-tumor tissues, the nucleic acid system comprising: a first DNA fragment that encodes a toxin gene that expresses a toxin that kills the genetically engineered bacterial strain； a second DNA fragment that encodes an antidote gene that expresses an antidote that negates the toxin； a first promotor that controls transcription of the antidote gene, such that glucose represses the transcription of the antidote gene； and a first constitutive promoter that causes constitutive expression of the toxin gene； wherein the second DNA fragment is transcribed in the solid tumors but not transcribed in the non-tumor tissues.
