Table 2. Mechanisms by which some bacteria cause colorectal cancers.

Organism	Mechanism of action
Enterococcus fecalis	DNA damage from increased production of hydroxyl radicals [178]
Peptostreptococcus anaerobius	Increases reactive oxygen species and cell proliferation [179]
Salmonella	Activation of STAT3 and the Wnt signaling pathway [180]
Fusobacterium nucleatum	Forms protein complex with beta-catenin and modulates its expression affecting the Wnt pathway [181]
Campylobacter species	Produces genotoxins leading to DNA damage [182]
Escherichia coli	Produces colibactin leading to DNA double-strand breaks and activation of DNA damage checkpoint pathway [183]
Bacteroides fragilis	Produces Bacteroides fragilis toxin [184]
Helicobacter pylori	Due to cytotoxin-associated gene, reactive oxygen species [185,186]
Clostridium septicum	A hypoxic and acidic tumor environment favors its growth and plays a role indirectly [187]