Clostridium botulinum is a spore-forming, anaerobic bacillus which produces a toxin that causes botulism. C. botulinum was first recognized and isolated in 1896 by Van Ermengem and is commonly found in soil.
These rod-shaped organisms grow best in low oxygen conditions. The bacteria form spores which allow them to survive in a dormant state until exposed to conditions that can support their growth. There are seven types of botulism toxin designated by the letters A through G; only types A, B, E and F cause illness in humans.
Each of the seven subtypes of C. botulinum produce seven different botulinum toxins (one per subtype). These are labeled with letters and are called A-G types (types C and D are not human pathogens). A "mouse protection" test determines the type of C. botulinum present (monoclonal antibodies used). In the United States, outbreaks are primarily due to types A, B (which are found in soil) or E (which is found in fish).¹
¹ Optimum temperature for types A & B is 35-40° C. Minimum pH is 4.6. It takes 25 min at 100°C to kill these types. Optimum temperature for type E is 18-25°C. Minimum pH is 5.0. It takes about 0.1 minute at 100°C to kill type E C. botulinum.
Clostridium botulinum is also used to prepare Botox, used to selectively paralyze muscles to temporarily relieve wrinkles. It has other "off-label" medical purposes, such as treating headaches.