Clostridium: A group of anaerobic bacteria (bacteria that thrive in the absence of oxygen). There are 100+ species of Clostridium. They include, for examples, Clostridium difficile, Clostridium perfringens (also called Clostridium welchii), and Clostridium botulinum.
Clostridium difficile is one of the most common causes of infection of the large bowel (the colon) in the US affecting millions of people yearly. Patients taking antibiotics are at risk of becoming infected with C. difficile. Antibiotics disrupt the normal bacteria of the bowel, allowing C. difficile bacteria to become established in the colon. Many persons infected with C.difficile have no symptoms. These people become carriers of the bacteria and can infect others. In other people, a toxin produced by C. difficile causes diarrhea, abdominal pain, severe inflammation of the colon (colitis), fever, an elevated white blood count, vomiting and dehydration. In severely affected patients, the inner lining of the colon becomes severely inflamed (a condition called pseudomembranous colitis). Rarely, the walls of the colon wear away and holes develop (colon perforation), which can lead to a life-threatening infection of the abdomen.
Clostridium perfringens, also known as Clostridium welchii), this is the most common agent of gas gangrene and also causes food poisoning as well as a fulminant form of bowel disease called necrotizing colitis.