Three-dimensional (3D) computer-generated image of a cluster of barrel-shaped Clostridium perfringens bacteria. The artistic recreation was based upon scanning electron microscopic (SEM) imagery. Clostridium perfringens (formerly known as C. welchii, or Bacillus welchii) is a Gram-positive, rod-shaped, anaerobic, spore-forming pathogenic bacterium of the genus Clostridium. Clostridium perfringens is everpresent in nature and can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates, insects, and soil. It has the shortest reported generation time of any organism at 6.3 minutes in thioglycollate medium. Clostridium perfringens is the third most common cause of food poisoning in the United Kingdom and the United States though it can sometimes be ingested and cause no harm.