Clostridium botulinum has been classified into eight different strains. Each strain releases the deadly toxin but in slightly different forms. Humans are susceptible to four of these eight toxins; the other four are deadly in cattle, sheep, and horses. C. botulinum is a strict anaerobe, meaning it survives only in conditions completely lacking oxygen. In fact, the presence of oxygen kills C. botulinum. However, the bacteria can survive for long periods of time by producing endospores. Endospores are small, protective capsules that surround the bacteria. They can withstand incredible extremes of temperature. The C. botulinum endospore can survive several hours at 212°F (100°C, the boiling point of water) and 10 minutes at 248°F (120°C). C. botulinum endospores also can survive at -374°F (-226°C). The endospores can even resist radiation. The botulism endospore is one of the most hardy organisms on Earth.
The botulinum toxin is in fact a group of seven closely related poisons produced by the bacteria. The fatal toxin the bacteria produces is a neurotoxin—it binds to nerve cells. Once bound, the toxin prevents the release of a neurotransmitter called acetylcholine from the nerve cells. Since nerve cells use the release of acetylcholine to transmit nerve impulses, preventing the release of acetylcholine stops the transmission of nerve impulses. Muscle paralysis eventually results.
The toxin targets nerve cells of the peripheral nervous system which govern the muscles associated with breathing. The muscles that control the tongue, pharynx, and ribs succumb swiftly to the toxin, becoming paralyzed within hours of ingestion of contaminated food. If rapid diagnosis is not made and treatment with an antitoxin (a substance that blocks the binding of the toxin to nerve cells) is not started, death can result quickly.