Keku et al. recently published a review called “The Gastrointestinal Microbiota and Colorectal Cancer” in the American Journal of Physiology – Gastrointestinal and Liver Physiology.

Although genes contribute to colorectal cancer (CRC), the gut microbiota are an important player. Correlational studies have observed changes in fecal microbiota composition in CRC compared to healthy controls; cancer is associated with reduced abundances of some butyrate-producing species. Transplanting feces from mice with CRC into germ-free mice leads to increased tumorigenesis.

Table 1 lists human studies of gut bacteria associated with CRC.
Table 2 lists animal studies of gut bacteria associated with CRC.

The article reviews some of the mechanisms by which the bacteria might induce tumorigenesis:
– Cell wall antigens and bacterial colicins
– Chronic inflammation
– Production of toxic metabolic byproducts

Authors emphasize that one environmental factor – a diet low in fiber – may impact the intestinal microbiota in a way that affects host cell physiology, cellular homeostasis, energy regulation, and/or metabolism of xenobiotics. This in turn may lead to chronic inflammation and CRC.

Now that we know the bacteria associated with CRC, authors say we must focus on gaining mechanistic insights. Information on microbiota functions will be important to consider.

Authors provided a reasonable overview of research to date, but did not mention one important paper by Zeller, et al., which recently presented data linking diet to CRC through microbiota functions. (Read more about the paper here.)

Keku TO, Dulal S, Deveaux A, Jovov B, & Han X. (2014) The gastrointestinal microbiota and colorectal cancer. Am J Physiol Gastrointest Liver Physiol doi: 10.1152/ajpgi.00360.2012