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Botulinum Clostridia

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Botulinum toxin–producing clostridia are anaerobic gram-positive organisms that form subterminal spores and are ubiquitous. Toxin production, however, requires spore germination, which occurs only with a rare confluence of circumstances: an anaerobic atmosphere, a pH of >4.5, low salt and sugar concentrations, and temperatures of 4–120°C. Although they are commonly ingested, spores do not normally germinate in the intestine. The various species of toxigenic clostridia—C. botulinum groups I, II, and III; C. argentinense (toxin type G); C. baratii (toxin type F); and C. butyricum (toxin type E)—can be differentiated on the basis of phenotypic characteristics, including specific biochemical properties and morphologic appearance on egg yolk agar. Strains of a given species can be distinguished by the antigenic specificity of the botulinum neurotoxin they produce; certain strains may produce more than one toxin serotype.…show more content…
Whether ingested, inhaled, or produced in the intestine or a wound, botulinum neurotoxin enters the vascular system and is transported to peripheral cholinergic nerve terminals, including neuromuscular junctions, postganglionic parasympathetic nerve endings, and peripheral ganglia. The central nervous system probably is not involved. Steps in neurotoxin activity include (1) heavy-chain binding to nerve terminals, (2) internalization in endocytic vesicles, (3) translocation to cytosol, and (4) light-chain serotype-specific cleavage of one of several proteins involved in the release of the neurotransmitter acetylcholine. Inhibition of acetylcholine release by any of the seven toxin serotypes results in characteristic flaccid paralysis. Recovery follows sprouting of new nerve
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