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Veterinary bacteriology: information about important bacteria
Veterinary bacteriology

Species/Subspecies: Clostridium tetani
Categories: Causes hemolysis; spore forming; motile
Etymology: Genus name: a small spindle.
Species epithet: of a tension (of tetanus which refers to the tension in the muscles which is caused by tetanus).
Significance:  [Very important]   
Type Strain: ATCC 19406 = CCUG 4220 = NCTC 279.
Macromorphology (smell):
C. tetani produces a very faint growth on FAA plates. Single colonies can hardly be observed, but a thin film of bacteria can often be discerned, because the bacteria swarm on moist agar plates. On dryer blood agar single medium sized colonies may be formed (4-6 mm in diameter). These colonies are flat, translucent and grayish with an irregular margin. A thin zone of β-hemolysis can often be observed around colonies on blood agar.
Micromorphology: Large rods (0.5-1.7 x 2.1-18.1 µm), which may appear single, in pairs or in short chains. Most strains are motile and have peritrichous flagella. Produce endospores, which usually are spherical and terminal. The spores may also be oval and subterminal.
Gram +/Gram -:
G+ (old cultures may appear as G-)
Metabolism: Anaerobic
Other Enzymes: Esculinase -, lecithinase -, tryptophanase V.
Fermentation of carbohydrates:
Other carbohydrates: C. tetani does not form acid by fermentation of carbohydrates.
Spec. Char.: Optimal growth temperature: 37°C.
Reservoir: C. tetani can be found in soil (particularly manured) and can be isolated from the gut of different animal species.
HostsDiseaseClinical picture
HorseTetanusSpastic paralysis, increased muscle stiffness, rigid motions, convulsions, strong reaction to external stimuli, difficulties to eat, prolapse of third eyelid, and finally paralysis of respiratory muscles
CattleTetanusMuscle contractions, spasms, tremors, straight tail, ceased rumen function, stiff legs, collapse
HumansTetanusPainful muscle contractions beginning with the face ("risus sardonicus" = sardonic smile) and neck, followed by torso and extremities. The cramps are often triggered by external stimuli and cause strangle.
Virulence Factors: C. tetani produces two exotoxins, tetanolysin and tetanospasmin, which are encoded by plasmid born genes. Tetanospasmin is a neurotoxin, which is similar to botulinum toxin in structure and mode of action, but they act on different parts of the nervous system. Tetanospasmin blocks the inhibitory nerve impulses by interfering with the release of neurotransmitters (glycine and γ-aminobutyric acid) and this in turn leads to a spastic paralysis. C.f. Clostridium botulinum.

The lethal dose of tetanospasmin for humans is approximately 2.5 ng/kg of body weight. Of natural toxins, only the botulinum toxin is more potent. Tetanolysin has a local necrotizing effect, which may facilitate the spread of C. tetani.

Genome Sequence:
Acc-noStrainSize (bp)Genome
NC_004557 E88 2 799 251 1c + 1c 

16S rRNA Seq.:
Acc-noStrainNumber of NTOperon
X74770 NCTC 279 1 515 

C. tetani belongs, together with about 80 other Clostridium spp., to cluster I, which use to be regarded as genus Clostridium sensu stricto. There are about 100 additional species described.
Reference(s): No. 33
Link: Botulinum + Tetanus Toxin Mechanism

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