Clostridium botulinum
المؤلف:
Cornelissen, C. N., Harvey, R. A., & Fisher, B. D
المصدر:
Lippincott Illustrated Reviews Microbiology
الجزء والصفحة:
3rd edition , p153-155
2025-07-16
388
C. botulinum causes botulism, which occurs in several clinical forms. Botulism is caused by the action of a neurotoxin that is one of the most potent poisons known and causes a flaccid paralysis. Contact with the organism itself is not required, and the the disease can be solely due to ingestion of toxin-contaminated food
. 1. Epidemiology: C. botulinum is found worldwide in soil and aquatic sediments, and the spores frequently contaminate vegetables and meat or fish. Under appropriate conditions, including a strictly anaerobic environment at neutral or alkaline pH, the organism germinates, and toxin is produced during vegetative growth. Because the toxin is often elaborated in food, outbreaks frequently occur in families or other eating groups.
2. Pathogenesis: There are several types of botulinum toxin, designated A through G, but human disease is almost always caused by types A, B, or E. The botulinum and tetanus toxins constitute a homologous set of proteins whose neurotoxicity arises from proteolytic cleavage of specific synaptic vesicle peptides, causing subsequent failure of neurotransmission. In contrast to tetanus toxin, which causes constant contraction , botulinum toxins affect peripheral cholinergic synapses by blocking the neuromuscular junction and inhibiting release of the neuro transmitter acetylcholine, preventing contraction and causing flaccid paralysis (Figure 1). Both botulinum and tetanus toxins are AB-type toxins comprised of an activity domain (A) and a binding domain (B).
Fig1. Mechanism of botulinum toxin. AcCoA = acetyl CoA.
3. Clinical significance:
a. Classic botulism: Food poisoning in which a patient first begins to experience difficulties in focusing vision, swallowing, and other cranial nerve functions, 12 to 36 hours after ingesting toxin-containing food but not necessarily viable organisms is classic botulism. There is no fever or sign of sepsis. A progressive paralysis of striated muscle groups develops, and mortality rate is about 15 percent, with the patient usually succumbing to respiratory paralysis. Recovery, which involves regeneration of the damaged nerves, is protracted, lasting several weeks.
b. Infant botulism: The most common form of botulism in the United States today is infant botulism, or a cause of floppy baby syndrome. An infant has yet to develop mature colonic microbial flora. Therefore, without competition, C. botulinum can colonize the large bowel of infants and produce toxin. The botulinum toxin is produced in vivo and slowly absorbed. Constipation, feeding problems, lethargy, and poor muscle tone are common early signs. Supplementation of infant foods (cereals or formula) with raw honey, which is contaminated with C. botulinum spores, may transmit the organ ism. The condition is possibly a cause of sudden infant death syndrome, but recovery is the usual outcome, following symptomatic treatment that may be prolonged.
c. Wound botulism: A rare form of botulism occurs when a wound becomes contaminated with the organism, and toxin is absorbed from that site. The molecular pathogenesis of this infection is similar to that of tetanus.
4. Laboratory identification: The organism can be cultured and identified by standard anaerobic methods. Toxin is also identifiable in serum, stool, and food.
5. Treatment and prevention: Antitoxin, which neutralizes unbound botulinum toxin, should be administered as soon as possible in suspected botulinal intoxication. A trivalent (A, B, E) horse anti serum is available from the Centers for Disease Control. Supportive measures, including mechanical ventilation, may be required. In wound and infant botulism, the infection can be treated with penicillin or other antibiotics to which the organism is sensitive. The toxin is inactivated at boiling temperatures, although killing of botulinal spores requires moist heat under pressure (autoclaving). [Note: Even the most severe cases of botulism do not result in immunity.]
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