Several bacteria are already linked to human cancers, and new evidence points towards a link between Escherichia coli (E. coli) and an increased risk of bowel cancer. Luckily there are things we can do to limit the risk posed by bacteria.
The links between bacteria and cancer have been studied for a long time. The connection was first publicised in the 19th century when Rudolf Virchow suggested that cancer may result from inflammation triggered by infections. Soon after, well known scientists Robert Koch and Louis Pasteur found bacteria in tumours.
Bacterial infections nearly always cause inflammation, which occurs when our immune system recognises an infection. Immune responses often involve the release of molecules called cytokines that help to cause inflammation. Short-term stimulation of inflammatory cytokines is good and helps fight infections, but chronic stimulation can contribute to cancer development. Inflammation is a key feature that researchers are interested in, and new knowledge could help us to reduce our cancer risk.
Many bacteria have been linked to cancer via inflammation – Helicobacter pylori and stomach cancer, Salmonella typhi and gallbladder cancer, Streptococcus bovis and bowel cancer. Considering what we know now, this isn’t all that surprising.
Trillions of bacteria live in your digestive system, with hundreds of different species of bacteria living in your bowel alone. Bowel cancers are responsible for the fourth highest number of cancer-related deaths worldwide, and yet only a small percentage of bowel cancers are linked to genetic risk. The majority of new cases occur somewhat randomly (sporadic cancers) or related to inflammatory bowel disease (IBD-associated cancers).
This is where bacteria become important.