Botulism toxin

     Clostridium botulinum is a large anaerobic bacillus that forms subterminal endospores. Clostridium botulinum is widely spread in the soil, lakes and pond sediments, or in decomposing vegetation. Thus the intestinal tract of birds, fish and mammals may contain, transient, this bacterium. There are seven types of the toxigenic organism, each producing an immunologically distinct form of botulism toxin. The botulism toxins are named with letters as A, B, C1, D, E, F and G. Not all strains of C. botulinum produce the botulism toxin. It is assumed that G toxin is encoded by a plasmid.

Botulism toxin

     Botulism toxin is specific for peripheral nerve endings at the motor plate. Botulism neurotoxin is primarily affecting the peripheral nervous system, with the special affinity for motor neurons by stimulating the motor plate. The first symptom of infection is muscle wasting. The botulism toxin is synthesized as a polypeptide chain with molecular weight around 150kDa.

     In this form the botulism toxin has a relatively low activity. Subsequently, the toxin is cleaved by a bacterial protease and possibly by the gastric protease which result in two fragments: a light chain (fragment A) with molecular mass of 50kDa and a heavy chain (fragment B) with a mass of about 100kDa. The two fragments remain linked via a disulfide bridge.

Mode of action of the botulism toxin

     The toxin prevents the release of chemical mediator (acetylcholine) in the motor plate. The heavy chain mediates the binding to the presynaptic receptors. The nature of these receptors is not known with certainty. It is possible that different varieties of the botulism toxin to bind to different receptors. The binding region of the toxin molecule is located near the carboxy-terminal tip of the heavy chain. Regarding the amino-terminal end of the heavy chain, it is deemed to form a channel through the neuron membrane, channel through which the light chain enters.

     Fragment A penetrate so in the endocitosis cell mediated by the receptor and which inhibit the acetylcholine release. The affected neurons are not able to release chemical mediators which cause paralysis of the motor system. The mechanism by which botulinum toxin inhibits acetylcholine release is not known but it is considered that the toxin is addicted of Zn (zinc).

Prevention and control

     The most important aspect of preventing botulism is the proper training and preparation of food. The C botulicum spores can survive to boiling at 100 degrees C for more than an hour. The toxin is sensitive to heat and thus, by boiling, is disabled.

Measures against transmission paths

• Using aseptic technique in hospitals
• The preparation of preserved food in private households, is to be made by boiling at least 10 minutes
• Avoid drinking canned food that changed in appearance, odor or color
• Contaminated food will be sterilized by boiling, autoclaving

Measures for the patients

• There will be discovered all those who ate the allegedly contaminated food.
• There is no specific prophylaxis (it's in study).

Treatment:

• Gastric wash, purgatives;
• Interment at intensive care;
• Serotherapy polyvalent serum A, B, E - 1-200000 IU, dose which may be repeated after 3-5 days;
• General care and correction of imbalances, bladder assistance, super infections treatment;
• Guanidine hydrochloride - increases the release of acetylcholine in the terminal nerve fibers.

     By assisting respiration and intensive care measures imposed on the rest, we managed to reduce the lethality of botulism from 60% to 25%.