Figure 1.

Bacteria living in tumours and their mechanisms as oncolytic bacteria. Genetically modified Clostridium are able to express cytosine deaminase (CD), which can convert the non-toxic pro-drug 5FC into the toxic antineoplastic drug 5FU, similar to Bifidobacteria and Salmonella typhimurium. Engineered Clostridium can also express nitroreductase (NTR) or TNF-α, killing tumour cells by converting pro-drugs or producing cytokines. Recombinant Salmonella typhimurium expresses flagellin B to activate TLR4 and TLR5, triggering stronger immune response to kill tumour cells. Engineered Listeria monocytogenes acts as a vaccine vector by expressing various antigens including NP, HPV-16 E7, PSA, and HER-2, generating cell-mediated immunity to eliminate tumours. Bacillus produces various bioactive metabolites against cancer cells.