Clostridium botulinum bacterium. Coloured scanning electron micrograph (SEM) of a Clostridium botulinum bacterium (yellow), the cause of botulism in humans. Botulism is a type of food poisoning caused by the powerful neurotoxin that this bacterium produces. C. botulinum occurs naturally in soil, but can also flourish in badly- preserved canned meat. The neurotoxin poisons the central nervous system and can cause lethal heart or lung failure. It is destroyed by thorough cooking, but the bacterium itself can survive heat in spore form. Magnification unknown.