Bacteria Play Critical Role in Driving Colon Cancers
Source: Johns Hopkins University School of Medicine
Summary: A study finds, patients with an inherited form of colon cancer harbor two bacterial species that collaborate to encourage the development of the disease, and the same species have been found in people who develop a sporadic form of colon cancer.
About 5% of colon cancers are caused by a hereditary syndrome called familial adenomatous polyposis (FAP), in which an inherited mutation launches a series of genetic changes that develop over time and eventually prompt the epithelial cells to turn malignant. FAP is a devastating disease that ultimately results in a surgical removal of the colon. Researchers from the Johns Hopkins University School of Medicine in one study found that patients with an inherited form of colon cancer harbor two bacterial species that collaborate to encourage the development of the disease, and the same species have been found in people who develop a sporadic form of colon cancer. And in the second study shows a possible mechanism behind how one of these species spurs a specific type of immune response, promoting, instead of inhibiting, the formation of malignant tumors. The complementary study findings were published in the journals Cell Host & Microbe and Science.
To investigate the relationship between the bacteria-caused biofilms and cancer formation, the research team examined colon tissue removed from 6 FAP patients. Tests showed patchy sections of biofilms distributed along the colon’s length in about 70% of the patients. They used gene probes to identify the particular bacterial species and found that the biofilms consisted mainly of two types, Bacteroides fragilis and Escherichia coli, a surprising finding since the colon contains at least 500 different types of bacteria. Tests on 25 additional colon samples from FAP patients showed that the B. fragilis strain was a subtype, called ETBF, which makes a toxin that triggers certain oncogenic, or cancer-promoting, pathways in colon epithelial cells and causes colon inflammation. The E. coli strain produced a substance called colibactin, which causes DNA mutations.
Prof. Cynthia Sears said, “The two new studies suggest a variety of strategies that researchers could test to prevent or even combat colon cancer. For example, it may be possible to prevent this disease by keeping the colon from becoming colonized by these two problematic bacteria, or by devising drugs or vaccines that target their toxins.”
Liam Chung et al. Bacteroides fragilis Toxin Coordinates a Pro-carcinogenic Inflammatory Cascade via Targeting of Colonic Epithelial Cells, Cell Host & Microbe (2018). DOI: 10.1016/j.chom.2018.01.007
C.M. Dejea el al., “Patients with familial adenomatous polyposis harbor colonic biofilms containing tumorigenic bacteria,” Science (2018). science.sciencemag.org/cgi/doi … 1126/science.aah3648