Streptococcus anginosus promotes gastric inflammation, atrophy, and tumorigenesis in mice. (https://pubmed.ncbi.nlm.nih.gov/38295787/)

These scientists wanted to understand how a certain bacteria called Streptococcus anginosus (S. anginosus) can cause problems in the stomach. They found that this bacteria was more common in people with a type of cancer called gastric cancer. So, they decided to study this bacteria in mice to see what it does.

First, they gave the mice S. anginosus and found that it caused a type of infection called acute gastritis, which is when the stomach becomes inflamed. Over time, the infection turned into a long-lasting problem called chronic gastritis. This caused the mice to have less of a certain type of cells in their stomach called parietal cells, and the cells that were left changed into a different type called mucinous cells. These changes can sometimes lead to cancer.

To make sure that S. anginosus was really causing these problems, the scientists did the same experiment but with mice that didn't have any other bacteria in their stomachs. They found that even without other bacteria, S. anginosus still caused the same problems, confirming that it was the main cause.

Next, they wanted to see if S. anginosus could make existing cancer grow faster. They used chemicals to make the mice have gastric cancer, and then they gave them S. anginosus. They found that the bacteria did make the cancer grow faster.

To understand how S. anginosus does all of this, the scientists looked at how it interacts with the cells in the stomach. They found that the bacteria has a protein on its surface called TMPC, which can attach to a receptor called Annexin A2 (ANXA2) on the stomach cells. This attachment helps the bacteria to stick to the cells and causes a chain reaction inside the cells called the MAPK pathway. This pathway can make the cells grow and divide more, and it also stops them from dying when they should.

To make sure that the attachment between TMPC and ANXA2 is really important, the scientists used mice that didn't have the ANXA2 receptor. They found that without this receptor, S. anginosus couldn't cause the chain reaction and the problems in the stomach didn't happen.

So, this study shows that S. anginosus is a bacteria that can cause stomach problems and even make cancer grow faster. It does this by attaching to stomach cells and activating a pathway that makes the cells divide more and not die when they should.

Fu K., Cheung AHK., Wong CC., Liu W., Zhou Y., Wang F., Huang P., Yuan K., Coker OO., Pan Y., Chen D., Lam NM., Gao M., Zhang X., Huang H., To KF., Sung JJY., Yu J. Streptococcus anginosus promotes gastric inflammation, atrophy, and tumorigenesis in mice. Cell. 2024 Jan 22:S0092-8674(24)00006-0. doi: 10.1016/j.cell.2024.01.004.