C. botulinum is prevalent in soil and marine sediments worldwide, most commonly as spores. These spores are found everywhere. While the spores are generally harmless, the danger can occur once the spores begin to grow out into active bacteria and produce neurotoxins. A neurotoxin is a poisonous chemical that affects the central nervous system. It can destroy, paralyze, or adversely affect nerves or nerve tissue. C. botulinum produces seven different types of neurotoxins designated by the letters A through G; only types A, B, E, and F cause illness in humans.
C. botulinum spores are often found on the surfaces of fruits and vegetables and in seafood. The organism grows best under low-oxygen conditions and produces spores and toxins. The toxin is most commonly formed when food is improperly processed (canned) at home. C. botulinum cannot grow below a pH of 4.6, so acidic foods, such as most fruits, tomatoes, and pickles, can be safely processed in a water bath canner. However, foods with a higher pH (most vegetables and meats) must be processed under pressure. Therefore, a pressure cooker should be used. The pressure cooker will reach high enough temperatures to destroy the C. botulinum spores.