Clostridium tetani Exotoxins

Classical bacterial exotoxins, such as diphtheria toxin, cholera toxin, clostridial neurotoxins, and the anthrax toxins are enzymes that modify their substrates within the cytosol of mammalian cells. To reach the cytosol, these toxins must first bind to different cell-surface receptors and become subsequently internalized by the cells. To this end, many bacterial exotoxins contain two functionally different domains. The binding (B-) domain binds to a cellular receptor and mediates uptake of the enzymatically active (A-) domain into the cytosol, where the A-domain modifies its specific substrate (see Figure 1). Thus, three important properties characterize the mode of action for any AB-type toxin selectivity, specificity, and potency. Because of their selectivity toward certain cell types and their specificity for cellular substrate molecules, most of the individual exotoxins are associated with a distinct disease. Because of their enzymatic nature, placement of very few A-domain molecules in the cytosol will normally cause a cytopathic effect. Therefore, bacterial AB-type exotoxins which include the potent neurotoxins from Clostridium tetani and C. botulinum are the most toxic substances known today. However, the individual AB-type toxins can greatly vary in terms of subunit composition and enzyme activity (see Table 2). 

Tetanus is a condition characterised by prolonged, involuntary contraction of the skeletal muscles. The condition can be localised or generalised. Tetanus is caused by the bacterium Clostridium tetani, an obligate, anaerobic, Gram-positive rod-shaped bacterium. The pathogen produces an exotoxin called tetanospasmin. Tetanospasmin is a potent neurotoxin which blocks neurotransmitter release from inhibitory neurons resulting in muscular contractions. C. tetani is not an invasive microbe, rather the spread of the toxin is due to... 

Exocytosis targeted exocytotoxins. a-Latrotoxin (black widow spider venom) causes a massive exocytotic release, followed by depletion of acetylcholine and other neurotransmitters. Botulinum toxins (A, B,C, D, E, F. G serotypes) are peptide exotoxins elaborated by a bacterium [Clostridium botulinum) that cause flaccid paralysis through inhibition of depolarization-induced release of acetylcholine at the skeletal neuromuscular junction. Tetanus toxin elaborated by bacterium [Clostridium tetani), is a polypeptide A-B exotoxin transported retrogradely along sensory neurons to the CNS, leading to tetanic paralysis. 

A-B Toxins are bacterial toxins composed of two peptide chains one (B) that binds to the invaded cell surface, and the other (A) containing the toxin which is then taken-up into the cell. Some examples of exotoxins secreted by the bacteria into the surrounding medium and highly toxic to certain tissues are pathogens causing botuiism (Clostridium botulinum), tetanus (Clostridium tetani) and diptheria (Corynebacterium diphtheria. An example of an A-B endotoxin is Vibrio cholerae. Botulinum toxin and tetanus toxin have their main toxic actions on neuronal tissues, so are described at NEUROTOXINS. 

Tetanus is a severe acute illness caused by the exotoxin of Clostridium tetani. Sustained muscle contractions are characteristic of tetanus. Tetanus toxin interferes with neurotransmitters that promote muscle relaxation leading to continuous muscle spasms. Death can be due to the tetanus toxin itself or secondary to a complication such as aspiration pneumonia, dysregulation of the autonomic nervous system, or pulmonary embolism. 

Tetanus is a rare disease in the United States, with fewer than 50 cases reported annually. It is caused by an exotoxin produced by Clostridium tetani, an anaerobic, spore-forming, gram-positive rod found widely in soil and in the gastrointestinal tract. Tetanus is typically seen in older persons (especially older women), recent immigrants, and intravenous dmg users who have not maintained adequate tetanus immunization. 

Exotoxins. Bacterial toxins which, in contrast to en-dotoxins, are secreted by living, mostly Gram-positive bacteria (Staphylococcus aureus E. Comyebacterium diphtheriae see diphtheria toxin Clostridium botuli-num see botulism toxin Clostridium tetani). E. are... 

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