Clostridia bacteria cause a variety of diseases including food poisoning, neurological disorders, gas gangrene, and food spoilage. In general, theses organisms produce several exotoxins and enzymes, which contribute to the local tissue damage and development of a disease. Clostridium botulinum is the most important pathogen of this genus. Clostridium perfringens is another significant organism of concern, responsible for foodbourne toxicoinfection and enteritis in animals.
Clostridium botulinum was defined in 1953 as the species designation for all organisms known to produce botulinum neurotoxin (BoNT) and thereby having the ability of causing botulism in humans and animals and is considered an agent for bioterrorism. The botulinum part of this species name is derived from botulus, the Latin word for sausage, since botulism was originally associated only with meat products.2
Botulinum neurotoxins (BoNTs) are the most potent toxins known, and when entering human or animal tissues and subsequently blood circulation, they block neurotransmitter release from nerve endings, causing neuroparalysis. BoNTs are classified as types A-G, with types A,B,E, and F causing disease to humans.3
Biology of Clostridium Botulinum
Clostridium botulinum is an obligate anaerobe which means that the organism does not require oxygen to function and exposure to atmospheric levels of oxygen is lethal. It is a motile, spore-forming, Gram-positive rod. It grows in animal intestines and spores are found in soil and plants. The botulinum neurotoxin is produced at temperatures as low as 3-15 degrees C. Optimum temperature for growth and toxin production is 95°F. The organism does not grow below pH 4.6. Spores are highly resistant to heat. Clostridium botulinum spores may have a low significance as a bioweapon because they do not survive well in the healthy adult human gut environment. However, spores present in food products subjected to heat treatment will germinate under favorable conditions to form vegetative cells. Vegetative cells will grow under anaerobic environment in food and produce botulinum toxin in sensitive to heat treatment. Thorough heating of the food prior to consumption will make the food safe.1
Sources of Clostridium botulinum
Most Clostridium species survive in soil and grow in animal intestines. Clostridium spores may be found in poorly or underprocessed canned foods (such as some home-canned foods), spices, sewage, and plants. The spores are heat resistant and can survive in the canned food when temperature used below 248°F. Low acidity (pH above 4.6), low oxygen and high water content favor spore germination and toxin production. Home-canned vegetables - beans, peppers, carrots, corn, asparagus, potatoes, and fish are implicated in outbreaks. Yogurt, cream cheese, and jarred peanuts have also caused botulism outbreaks.
Some samples of honey have been reported to contain relatively high numbers of spores of C. botulinum. C. botulinum cannot multiply in honey because of the high sugar content. There is evidence that if bees are diseased, for example affected by foulbrood, C. botulinum can multiply in dead bees and this can result in high number of C. botulinum spores in the honey.4
Humans can harbor C. botulinum in their gastrointestinal (GI) tract. Low-level toxin absorption results in listlessness and low blood pressure (hypotonia), but the course of the disease can be fulminant. Infant botulism has been proposed as a cause of sudden infant death syndrome.5
- Foodborne microbial pathogens: mechanisms and pathogenesis. Arun K. Bhunia
- Clostridium botulinum: ecology and control in foods. Andreas H. W. Hauschild, Karen L. Dodds
- Food-borne pathogens: methods and protocols. Catherine Adley
- Guide to foodborne pathogens. Ronald G. Labbé, Santos García
- Mandell, Douglas and Bennett's principles and Practice of Infectious Diseases