Enterococcus faecalis, a human intestinal commensal, triggers the production of trans-4-hydroxy-2-nonenal (4-HNE) by macrophages via COX-2, which synergistically reinforces the damage of COX-2 to the DNA of the target cells through the bystander effect, leading to the development of CRC 92. This evidence concerns the gene PTGS2 and colorectal carcinoma.