Clostridium botulinum bacteria. Coloured scanning electron micrograph (SEM) of Clostridium botulinum bacteria (rod-shaped), the cause of botulism in humans. Botulism is a type of food poisoning caused by the powerful neurotoxin that these bacteria produce. 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 bacterial cells can survive heat in the form of spores. Magnification: x6700 when printed 10 centimetres wide.