These pathogens, as demonstrated in animal studies, interact with the immune system, produce metabolites linked to cancer, and release factors toxic to DNA.
Dysbiosis in Colorectal Cancer
The cascade can sometimes lead to colorectal cancer (CRC). Certainly, the involvement of the microbiota is becoming clearer. Many changes in the bacterial composition of the gut have been reported in colorectal cancer, suggesting a major role of dysbiosis. Still murky however is whether these differences are drivers or responses to cancer.
Nevertheless, the interplay between forces favorable to cancer and those attempting to thwart it makes for provocative research and a possible role for probiotics.
Five Pathogens in CRC
To help define how the gut microbiome in the figures in colorectal cancer, a group of researchers summarized five of the wayward bacteria and their specific mode of carcinogenesis in CRC. By establishing the mechanisms, researchers will be better able to target results of dysbiosis, possibly via microbial manipulation.
The gut microbiome and colorectal cancer: a review of bacterial pathogenesis in the Journal of Gastrointestinal Oncology detailed implicated pathogenic microorganisms including:
Sulfidogenic bacteria such as Bilophila wadsworthia
These produce hydrogen sulfide which damages DNA leading to mutations; also these bacteria are found in a high number of sporadic CRCs.
S. bovis may promote the transition to cancer and is also attracted to the collagen-rich neoplasia environment where it may hasten disease progression.
H. pylori is well-known as a culprit in gastric cancer and is considered a definite carcinogen. The bacterium induces gastritis through infection of epithelial cells. It also promotes inflammation and carcinogenesis through multiple mechanisms.
As part of the normal microbiota of the human colon, B. fragilis is generally beneficial. But it can turn on us. If displaced into the bloodstream or surrounding tissue following surgery, disease, or trauma, infection can result. B. fragilis is present and more concentrated in the mucosa of later-staged CRC compared to nearby non-cancerous tissue. This bacterium is a good example of the opportunistic nature of some microbes.
C. septicum can cause bacteremia and gas gangrene (often fatal). C. septicum does not appear to initiate carcinogenesis but does likely have a symbiotic relationship with the growth of already developing malignancies.
Bacterial microbiota modifications could represent novel prognosis markers and/or targets for innovative therapeutic strategies against CRC. Probiotics may one day figure in those plans.