Bacteria for targeting tumors and treating cancer

A bacterium for targeting tumors and treating cancer, each comprising:

• a nucleic acid system;
• and
• a gene that encodes a cytotoxin that kills tumor cells,
• wherein the nucleic acid system comprises:
• a first DNA fragment that encodes a toxin that kills the bacterium;
• a second DNA fragment that encodes an antidote that negates the toxin, the second DNA fragment being transcribed at tumor tissues but not transcribed at non-tumor tissues;
• a promoter of an antidote gene that is operably linked to the second DNA fragment and represses transcription of the second DNA fragment under control of a glucose level such that the antidote is expressed at the tumor tissues but not expressed at the non-tumor tissues;
• and
• a constitutive promoter of a toxin gene that is operably linked to the first DNA fragment and causes constitutive transcription of the first DNA fragment such that the toxin is expressed at the tumor tissues and the non-tumor tissues;
• wherein a random sequence that consists of 5-6 nucleotides that replaces the original 5-6 nucleotides of the genetically engineered bacterial strain is located immediately upstream of the second DNA fragment;
• wherein a pair of the toxin and the antidote is selected from the group consisting of a CcdB-CcdA pair, an AvrRxo1-Arc1 pair, a Hha-TomB pair, and a PaaA2-ParE2 pair;
• wherein the second DNA fragment is transcribed at a glucose environment with a concentration lower than 0.424 mM but not transcribed at a glucose environment with a concentration higher than 1.22 mM;
• and
• wherein the random sequence is GCCTT or TGTCT.