VetBact logo


Swedish University of Agricultural Sciences

Veterinary bacteriology: information about important bacteria
Veterinary bacteriology

Species/Subspecies: Clostridium botulinum, group I
Categories: Causes hemolysis; spore forming; motile; notifiable diseases and bacteria
Etymology: Genus name: a small spindle.
Species epithet: refers to sausage.
Significance:  [Very important]   
Type Strain: Typ A: ATCC 25763. Referensstammar: Proteolytisk typ B: ATCC 7949. Proteolytisk typ F: ATCC 25764.
Macromorphology (smell): Large greyish white colonies (5 mm in diameter) with very irregular edges, which usually produce β-hemolysis on blood agar.
Micromorphology: Large spore forming rods (0.6-1.4 x 3.0-20.2 µm). Most of the strains are motile. Gives hemolysis on bloodagar.
Gram +/Gram -:G+ (kan vara svår att gram-färga).
Metabolism: Anaerobic
Other Enzymes: Esculinase +, lecithinase -, tryptophanase -.
Biochemical Tests: Hydrogen sulphide (H2S) +.
Fermentation of carbohydrates:
Other carbohydrates: Fructose (-), galactoes -, mannose -, ribose -, xylose -.
Spec. Char.: Proteolytic bacteria produce phenols, indols and ammonia from the digestion of proteins.
Reservoir: Soil, carcasses, meat, fish, canned products.
Disease:Botulism or botulinus intoxication is a serious and potentially fatal disease in humans and animals. Botulism is usually an intoxication caused by intake of preformed toxin. It may also happen that spores of C. botulinum germinate in the intestine or in a deep wound and the bacteria may then start to produce toxin. This condition is termed a toxicoinfection.
Hosts: Or rather Animals that are sensitive to the toxins: The sensitivity for different types of botulinum toxin vary between different animal species.

  • Toxin type A: humans, infants (toxicoinfection), poultry, mink, dog, pig (and cattle).
  • Toxin type B: humans, infants (toxicoinfection), foals (toxicoinfection), horses and cattle.
  • Toxin type F: humans.
Clinical Picture: Flaccid muscular paralysis.
Virulence Factors: C. botulinum strains within group I produce botulinum toxin type A, B or F

The different toxin types have the same basic structure and mechanism of action, but are serologically distinct. Botulinum toxin is a neurotoxin, which is similar to tetanospasmin in structure and mode of action, but they act on different parts of the nervous system. Botulinum toxin is (like tetanospasmin) composed of two protein subunits and one is a protease that destroys the fusion protein to which vesicles containing acetylcholine should bind. Thereby inhibiting the signal transduction between the efferent (= motoric) nerve and muscle cells by preventing vesicles from anchoring to the membrane to release acetylcholine.

This results in a flaccid paralysis. C.f. Clostridium tetani.

Botulinum toxin is very potent, and the lethal dose for humans is approximately 1 ng/kg body weight.

Genome Sequence:
Acc-noStrainSize (bp)Genome
NC_009697 ATCC 19397 (toxin type A) 3 863 450 1c + 0 

16S rRNA Seq.:
Acc-noStrainNumber of NTOperon
L37585 ATCC 25763T 1 453 

About 180 differens species have been descibed within genus Clostridium. C. botulinum can be classified into four different phenotypic groups: I-IV. C. botulinum-strains within group I are most closely related to Clostridium sporogenes and Clostridium putrificum and not to any of the other three phenotypic groups of C. botulinum.
Legislation: In Sweden, botulism in animals and humans is notifiable to the Swedish Board of Agriculture and the Public Health Agency of Sweden, respectively. Clostridium botulinum belongs to category A as a potential bioterrorism agent according to NIAID.
Comment:Clostridium botulinum actually represents four different species (phenotypic groups), all of which have at least one of the botulinum toxin genes. The type strain is of toxin type A. In the case of C. botulinum, you can really say that taxonomy is not consistent with phylogeny.
Reference(s): No. 4, 33
Link: Botulinum + Tetanus Toxin Mechanism

Recently Updated

Recent blog posts

Swedish University of Agricultural Sciences