Many bacteria, such as Escherichia coli and Clostridium, are normally found in the colon. Some bacteria are able to break down undigested fiber into glucose. Bacteria are also able to synthesize certain vitamins, especially vitamins K and B12. The presence of large colonies of beneficial bacteria inhibits the growth of pathogenic bacteria. In addition, the bacteria ferment some of the indigestible carbohydrates, including cellulose, contributing to the production of intestinal gas, or flatus (from the Latin, meaning “blowing”).