Finally, a study on colon cancer mice showed that Gammaproteobacterial cytidine deaminase expression, encoded by the cdd gene, induced gemcitabine resistance showing that intratumor bacteria can contribute to the therapy efficacy.98 Based on comparative genomics, 660/5,451 microbial genomes, spanning 660 species, 224 genera, and 12 phyla, carry the cdd gene (Table S3).16 Here, CDA is linked to malignant colon neoplasm.