Streptococcus gallolyticus actively promotes tumor growth in cell cultures and in mice
Colorectal cancer, cancer of the colon or rectum, is the 3rd most commonly diagnosed cancer in men and women. The lifetime risk of developing colorectal cancer is about one in 21 for males and one in 23 for females. Colorectal cancer is the second most likely (1.82% risk of dying from it) to kill a person. The first being lung caner (5.31%), while breast cancer (1.38%) is the third. Only 11% of patients with stage IV colorectal cancer have a 5-year relative survival rate.
Estimated new cases in men and women in 2016.
Several lifestyle-related factors have been linked to colorectal cancer. To decrease the chances of being diagnosed with colorectal cancer, experts advise people to stop smoking, decrease intake of alcohol and red meat, keep active, maintain a healthy weight, and get screened for colon cancer.
Ways to Lower Your Risk for Colon Cancer
The first case of a bacteria associated with cancer was reported in 1951. Scientist have known for a while now that people infected with Streptococcus gallolyticus subspecies gallolyticus (formerly Streptococcus bovis) are more likely to have colorectal cancer.
The role of immune cells in the gut microbiota-related colorectal carcinogenesis.
"This association was well established in the clinical literature," said Dr. Yi Xu, associate professor at the Texas A&M Institute of Biosciences and Technology and principal investigator of the study. However, it was not clear whether the relationship was cause or effect - that S. gallolyticus promote cancer development or if the bacteria grow better in an environment near the tumor cells.
Streptococcus gallolyticus subsp. gallolyticus promotes colorectal tumor development
Ritesh Kumar and Jennifer L. Herold of Texas A&M Health Science Center and co-investigators studied the relationship between S. gallolyticus and colorectal cancer. To answer this question they looked at cell cultures, an animal model of colorectal cancer and tissue from human tumors. First, they grew colorectal cancer cells and S. gallolyticus together in cell cultures and found that the presence of the bacteria did promote proliferation of colorectal cancer cells. The cell culture study also showed that when the production of a protein, called β-catenin, was reduced in a cell, S. gallolyticus did not promote proliferation of colorectal cancer cells. This points to a potential pathway through which the bacteria stimulate cancer development. Findings in tissue culture were similar to what the researchers found in animal models of colorectal cancer. Those treated with S. gallolyticus developed more tumors and had increased production of the β-catenin protein. The team also studied normal and tumor tissue samples from over 100 human colorectal cancer patients and discovered that most were infected with S. gallolyticus. This confirms the results of an earlier seroepidemiological study, which reported a statistically significant association of exposure to S. gallolyticus antigens and colorectal cancer. Their conclusions and findings were published in PLOS Pathogen.
"There is still a lot more that we need to find out," Xu said. "For example, we don't know whether the continuous presence of the bacteria is necessary for cancer proliferation or if the gastrointestinal tract can be transiently colonized by the bacteria and still cause problems." Still, Xu reckons that this is something that oncologists should keep in mind. She said, “Clinicians need to take into consideration whether patients harbor this pathogen and how that is going to influence the development of cancer”.
The study clearly showed that a bacterium with a well-documented clinical association with colorectal cancer is also important in the development of the disease. These findings may help in the search for new strategies for improving diagnosis and treatment of colorectal cancer and possibly pave the way for the development of a vaccine against colorectal cancer caused by S. gallolyticus.