Streptococci promote growth of intestinal tumors

Direct contact between cancer cells and Streptococcus gallolyticus bacteria stimulates cell division and accelerates tumor growth

Direct detection of Streptococcus gallolyticus in human cancer tissue by immunofluorescence microscopy: The arrows indicate the red-colored streptococci.

Houston (USA) - When streptococci enter the blood, they can infect the heart and cause endocarditis. If the pathogens are a certain subspecies of Streptococcus gallolyticus, the patients have a significantly increased risk of colorectal cancer. The fact that there is a causal relationship between cancer and this bacterial infection has now been demonstrated by American physicians for the first time. The bacteria amplify tumor growth by attaching to cancer cells and increasing the production of a signal protein that accelerates cell division rate. The new results could be important for preventative measures, diagnosis and therapy of colorectal carcinoma, the researchers explain in the "PLoS Pathogens" paper.

"Until now it was not known whether these streptococci play an active role in the development of tumors, or whether they only increase as a result of the cancer in the vicinity of the tumors," write the scientists around Yi Xu from the Texas A & M Health Science Center in Houston , They first investigated the influence of Streptococcus gallolyticus subsp. In experiments with cell cultures. Gallolyticus - formerly called Streptococcus bovis - refers to the proliferation of human colorectal cancer cells. In three of the five cancer cell lines used, the addition of the streptococci into the culture medium caused accelerated proliferation of the cancer cells within two days. It is likely that the different types of colorectal cancer cells react to the presence of the bacteria only if they have certain surface structures that allow attachment. The stimulating effect on the rate of division presupposed the direct contact between microbes and tumor cells, which was not mediated by substances that released the bacteria into the nutrient medium. Other streptococcal species had no effect.

Further studies have shown that the attachment of the streptococci stimulated the production of beta-catenin in the cancer cells. This protein is involved in a signaling pathway that plays a role in cancer development. When the researchers blocked the beta-catenin formation, the effect of the bacteria remained. The cancer-promoting effect of the microbes was confirmed in experiments with mice infected with human intestinal tumors. After repeated administration of the streptococci via a probe, more tumors and beta-catenin production increased in the cancer tissue. Finally, the medical staff examined 148 tumor samples from patients. In 74 percent of the samples they were able to detect Streptococcus gallolyticus bacteria. In healthy tissue of the patients it was still 47 percent. Obviously, colon cancer patients are often also colonized by these germs if they are not suffering from endocarditis.

It is still not known how the streptococci stimulate colorectal cancer cells to produce beta catenin, so they divide faster. Also, why not all colon types react equally to the bacteria, still needs to be clarified. The individual composition of the intestinal flora could influence how much the cancer-promoting effect of the microbes is. Although Streptococcus gallolyticus bacteria were found in previous studies also in the gut of every tenth healthy person. But at least if the germs are detectable in the blood, control investigations would be appropriate for signs of colon cancer.