Clostridium acetobutylicum
Clostridium aerotolerans
Clostridium botulinum
Clostridium colicanis
Clostridium difficile
Clostridium formicaceticum
Clostridium novyi
Clostridium perfringens
Clostridium tetani

Clostridium is a genus of Gram positive anaerobic spore-forming bacteria.

There are many species of Clostridium but the four main species causing human disease are:

• Clostridium botulinum, an organism producing a toxin in food that causes botulism.
• Clostridium difficile, which can overgrow other bacteria in the gut during antibiotic therapy, causing pseudomembranous colitis.
• Clostridium perfringens, which gets into wounds, and is an important cause of gas gangrene.
• Clostridium tetani, the causitive organism of tetanus (lockjaw).