Clostridium, genus of gram-positive bacteria (see Gram's stain), several species of which cause significant, potentially deadly diseases in humans as a result of the toxins that each produces. Clostridium bacteria are rod-shaped and anaerobic, that is, they live in the absence of oxygen; they are common in the soil. C. botulinum, which grows in improperly canned food, produces neurotoxins that when ingested cause the form of food poisoning known as botulism. C. difficile, commonly known as C. diff, is usually transmitted in hospitals and nursing homes as a result of poor personal hygiene and insufficient disinfection; a person taking antibiotics, which kills normal intestinal bacteria, is more susceptible to the bacterium. Infection may cause fever, nausea and abdominal pain, diarrhea, and, in more severe cases, colitis. Infection is most deadly in those over 65 years of age. Since 2001 a more virulent and drug-resistant strain has of C. difficile has developed, making infection increasingly difficult to treat. Treatment typically involves stopping the antibiotic that promoted the infection and taking the antibiotics metronidazole (Flagyl; in milder cases) or vancomycin (in more severe cases); in the most extreme cases, the colon may be surgically removed. C. perfringens infection causes gas gangrene; it generally occurs in the body where trauma, surgery, or another cause has resulted in diminished blood supply. Within a week, fever and pain at the infection site results as the toxins released by the bacteria kill muscle cells; if untreated, muscle necrosis rapidly develops and spreads, leading to death. Tetanus results when C. tetani infects body tissues through a puncture wound or trauma. C. tetani is common in the digestive tract, but its toxins are destroyed digestive enzymes.