Colitis means an inflammation of the colon. One of the causes of colitis is an infection with bad bacteria. One such bacteria is called clostridium difficile, commonly called c. diff in the medical field. The colon normally has many beneficial bacteria in it. But some antibiotics can kill most of these good bacteria and leave room for this c. diff to grow. C. diff produces a toxin which damages the colon wall. In Image 1 you see a patchy inflammation in the bowel wall. It is a mild case. In Image 2 there are fluffy membranes caused by exudate and white blood cells. This in an advanced, serious case called pseudomembranous colitis. It is treated with one of two antibiotiecs, metronidazole (Flagyl) or vancomycin.